Computational and Experimental Confirmation of the Diradical Character of para-Quinonedimethide

The ground-state structure of the parent para-quinonedimethide (p-QDM) molecule is generally represented in its closed shell form, i.e., as a cyclic, nonaromatic, through-conjugated/cross-conjugated hybrid comprising four C═C bonds. Nonetheless, p-QDM has been theorized to contain a contribution from its open-shell aromatic singlet diradical form. VBSCF calculations identify an open-shell contribution of 29% to the structure, while CASPT2(16,16)/def2-TZVP and ωB97XD/aug-cc-pVTZ calculations predict that dimerization proceeds along an open-shell singlet diradical pathway with a low (77 kJ/mol) barrier toward dimerization, which occurs by way of C-C bond formation between the exocyclic methylene carbons. A similar low (98 kJ/mol) barrier exists toward the reaction between a p-QDM molecule and the radical trap TEMPO. These predictions are verified experimentally through the isolation of bis-TEMPO-trapped p-QDM, its C-C coupled dimer, and by demonstrating that a mixture of p-QDM and TEMPO can initiate the radical polymerization of n-butyl acrylate at ambient temperature. In contrast to p-QDM, tetracyanoquinone (TCNQ) neither dimerizes nor reacts with TEMPO, despite having a similar diradical character to p-QDM. This lack of reactivity is consistent with both a higher kinetic barrier and a thermodynamically unfavorable process, which is ascribed to destabilizing steric clashes and polar effects.

Probing Ligand Binding Sites on Large Proteins by Nuclear Magnetic Resonance Spectroscopy of Genetically Encoded Non-Canonical Amino Acids

N6-(((trimethylsilyl)-methoxy)carbonyl)-l-lysine (TMSK) and N6-trifluoroacetyl-l-lysine (TFAK) are non-canonical amino acids, which can be installed in proteins by genetic encoding. In addition, we describe a new aminoacyl-tRNA synthetase specific for N6-(((trimethylsilyl)methyl)-carbamoyl)-l-lysine (TMSNK), which is chemically more stable than TMSK. Using the dimeric SARS-CoV-2 main protease (Mpro) as a model system with three different ligands, we show that the 1H and 19F nuclei of the solvent-exposed trimethylsilyl and CF3 groups produce intense signals in the nuclear magnetic resonance (NMR) spectrum. Their response to active-site ligands differed significantly when positioned near rather than far from the active site. Conversely, the NMR probes failed to confirm the previously reported binding site of the ligand pelitinib, which was found to enhance the activity of Mpro by promoting the formation of the enzymatically active dimer. In summary, the amino acids TMSK, TMSNK, and TFAK open an attractive path for site-specific NMR analysis of ligand binding to large proteins of limited stability and at low concentrations.

A temperature switchable pyridyl-zinc(II) side arm porphyrin with functionality for surface immobilisation

A pyridyl side arm porphyrin incorporating C[Formula: see text] alkyl chains at the periphery of the porphyrin suitable for surface immobilisation on HOPG has been synthesised and tested for two state switching in solution. Temperature switching, involving reversible complexation of a covalently appended pyridyl side arm to the Zn(II) porphyrin, was comprehensively characterised by using variable temperature 1H NMR (-30 to +100[Formula: see text]C) and UV-vis (10 to 90[Formula: see text]C) in toluene. Molecular modelling assisted in understanding strain within the complex.

The effect of deuteration on the keto-enol equilibrium and photostability of the sunscreen agent avobenzone

The remarkable properties of deuterium have led to many exciting and favourable results in enhancing material properties, for applications in the physical, medical, and biological sciences. Deuterated isotopologues of avobenzone, a sunscreen active ingredient, were synthesised to examine for any changes to the equilibrium between the diketone and enol isomers, as well as their UV photostability and photoprotective properties. Prior to UV irradiation, deuteration of the diketone methylene/enol moiety (i.e. avobenzone-d2) led to an increase in the % diketone compared to non-deuterated, determined by 1H NMR experiments in CDCl3 and C6D12. This can be rationalised from two angles; mechanistically by a deuterium kinetic isotope effect for the CH vs. CD abstraction step during tautomerisation from the diketone to the enol, and a weaker chelating hydrogen bond for the enol when deuterated allowing increased equilibration to the diketone. Avobenzone-d2 was further examined by solid state 13C NMR. The higher % diketone for avobenzone-d2 was postulated to favour increased photodegradation by a non-reversible pathway. This was investigated by UV irradiation of the avobenzone isotopologues in C6D12, both in real time in situ within the NMR by fibre optic cable as well as ex situ using sunlight. An increase in the relative amount of photoproducts for avobenzone-d2 compared to non-deuterated was observed by 1H NMR upon UV irradiation ex situ. Overall, the study demonstrates that deuteration can be applied to alter complex equilibria, and has potential to be manifested as changes to the properties and behaviour of materials.

A Tetra-Porphyrin Host Exhibiting Interannular Cooperativity

Recently identified as another form of cooperativity, interannular cooperativity is rarely observed in supramolecular chemistry. A tetra-porphyrin molecular tweezer with two bis-porphyrin binding sites is reported that exhibits archetypal interannular cooperativity when complexing 1,4-diazabicyclo[2.2.2]octane (DABCO). The UV/Vis titration data best supported a 1:2 plus 2:2 plus 1:4 complexation model (host:guest), giving K₁₂ =6.32×10¹³  m^-2 , K₂₂ =3.04×10²⁰  m^-3 , and K₁₄ =1.92×10¹⁶  m^-4 in CHCl₃ . The NMR titration data supported the formation of two sandwich species, including tetra-porphyrin⋅(DABCO)₂ as the major species, although there are speciation differences between UV/Vis and NMR concentrations. Using statistical analysis, interannular cooperativity (γ) for tetra-porphyrin⋅(DABCO)₂ was determined to be negative (γ=2.41×10^-3 ), which may be explained by DABCO being too small to be optimally bound simultaneously at both bis-porphyrin binding sites.

Molecular tweezers with a rotationally restricted linker and freely rotating porphyrin moieties

The effect of the degree of conformational rigidity and/or flexibility on preorganisation in artificial molecular receptors continues to be actively explored by supramolecular chemists. This work describes a bis-porphyrin architecture, linked via a rigid polycyclic backbone, in which a sterically bulky 2,3,5,6-tetramethylphenyl diimide core restricts rotation to afford two non-interconvertible tweezer conformations; syn- and anti-. After separation, the host-guest chemistry of each conformation was studied independently. The difference in host geometry allows only the syn-conformation to form a strong 1 : 1 bis-porphyrin complex with the diamino ligand 1,4-diazabicyclo[2.2.2]octane (DABCO) (K11 = 1.25 × 108 M-1), with the anti-conformation adopting a 2 : 2 sandwich complex with DABCO (K22 = 5.57 × 1017 M-3).

Identification of the Main Intermediate Precursor of l-Ergothioneine Biosynthesis in Human Biological Specimens

A capillary electrophoresis coupled to tandem mass spectrometry (CE–MS/MS) has been used to make a qualitative determination of hercynine—the main precursor of l-ergothioneine biosynthesis—in some key human biological specimens, such as urine, whole blood, plasma, and saliva. From semiquantitative analysis results, the highest concentrations of hercynine were detected in saliva and whole blood, whereas much lower concentrations were measured in urine and plasma. Whole blood was the biological matrix with the highest concentration of l-ergothioneine followed by plasma, saliva, and urine. The antioxidant effects attributed to l-ergothioneine, along with its peculiar antioxidant mechanism, offer a possible explanation for the presence of the hercynine, as well as its concentration, in the considered biological matrices.

Tetra-porphyrin molecular tweezers: two binding sites linked via a polycyclic scaffold and rotating phenyl diimide core

The synthesis of a tetra-porphyrin molecular tweezer with two binding sites is described. The bis-porphyrin binding sites are aligned by a polycyclic scaffold and linked via a freely rotating phenyl diimide core. Synthesis was achieved using a divergent approach employing a novel coupling method for linking two polycyclic units to construct the core, with a copper(ii)-mediated phenyl boronic acid coupling found to extend to our polycyclic imide derivative. We expect this chemistry to be a powerful tool in accessing functional polycyclic supramolecular architectures in applications where north/south reactivity and/or directional interactions between modules are important. Porphyrin receptor functionalisation was undertaken last, by a four-fold ACE coupling reaction on the tetra-epoxide derivative of the core.

Technical note: validation of electronic feeding stations as a swine research tool

Electronic feeding stations (EFS) were developed to automate data collection of individual animals housed in a group environment. In order for scientists to use EFS, such as feed intake recording equipment (FIRE), in research, data recorded electronically cannot differ from data recorded on calibrated scales. The objectives of 2 studies were to determine if data recorded by 2 FIRE stations (FIRE1 and FIRE2) were different from the same data recorded by calibrated scales and determine differences between the 2 independent FIRE stations. Body weight of pigs recorded by the platform scales of both FIRE stations did not differ (P > 0.6) from calibrated scales during a 21-d comparison (study 1). The weight of calibrated check weights recorded by the platform scale of FIRE1 tended to be less (P = 0.1) than the weight of check weights during a 126-d comparison (study 2). Feed disappearance recorded by FIRE1 was greater (P < 0.01) than recorded by calibrated scales during study 2. Feed dispensed to the FIRE trough and compared with calibrated scales did not differ (P ≥ 0.17) for either FIRE station during study 2. There were no differences (P ≥ 0.15) between FIRE1 and FIRE2 for any measured variables. The FIRE stations were not recalibrated during study 1. The platform scale of FIRE2 was recalibrated during study 2 when the percentage error between calibrated check weights and the weight recorded by FIRE exceeded 2.5%. The trough scales of FIRE1 and FIRE2 were recalibrated during study 2 when the percentage error between true weight of dispensed feed and the average recorded FIRE weight exceeded 4%. Establishing more stringent criteria for recalibration may have reduced differences among weights recorded by calibrated scales and weights recorded by FIRE. These data suggest that FIRE stations can be used in research; however, adequate verification procedures and recalibration criteria must be followed to ensure accuracy of data.

Optimising operation of a biological wastewater treatment application

The objective of this work was to optimize (minimize) the compressed air required to control the rate of ammonia removal in a commercially operated wastewater bioreactor, while still maintaining operation within environmental consent limits. In order to do this, a nonlinear dynamic model based on the International Association on Water Quality (IAWQ) activated sludge model No. 3 was developed, expressing the nitrification kinetics and hydraulic dynamics of the system. From this model a steady state representation of the plant was derived, and simulated for various load characteristics experienced at the facility, and as a result an optimal load profile was developed for the compressed air distribution to the four aerobic zones. The optimal load profile will ensure that the amount of compressed air required to control the rate of ammonia removal is optimized.

Imaging of the cervical spine and its role in clinical decision making

Thorough imaging of the cervical spine often requires more than one test. The many available options from which to choose can often lead to redundancy and confusion regarding the best test series. In an effort to make the process of choosing the most effective imaging series more efficient, we review the current literature on cervical imaging and, from the information gathered, construct a diagnostic imaging algorithm for evaluating the cervical spine.

Parasympathetic innervation of the meibomian glands in rats

PURPOSE

To determine the location of parasympathetic neurons that innervate the meibomian glands in rats.

METHODS

The B subunit of cholera toxin (CTB), fast blue, and a retrograde transneuronal tracer, the Bartha strain of pseudorabies virus (PRV-Ba), were injected into the upper eyelids of adult Sprague-Dawley rats after sectioning the ipsilateral branches of the facial nerve and resecting the superior cervical ganglia. Brains and orbital tissues were processed for the immunohistochemical detection of PRV-Ba and CTB. In selected cases, series of brain sections were double labeled for PRV-Ba and tyrosine hydroxylase to determine the relationship between the A5 noradrenergic cell group and superior salivatory nucleus, or for PRV-Ba and choline acetyltransferase to establish the neurochemical phenotype of parasympathetic preganglionic neurons.

RESULTS

Labeled ganglionic cells were diffusely distributed within the ipsilateral pterygopalatine ganglion (PPG) and along the more proximal portions of the greater petrosal nerve (GPN). Labeled preganglionic neurons were cholinergic and were located immediately dorsolateral to the rostral-most portion of the facial nucleus and caudal superior olive, where they intermingled with A5 noradrenergic cells.

CONCLUSIONS

The meibomian glands and other structures within the lid margin are subject to parasympathetic regulation by ganglion cells diffusely distributed within the PPG and along more proximal portions of the GPN. Cholinergic parasympathetic preganglionic neurons that project to meibomian gland-innervating ganglion cells are located immediately lateral, dorsal, and rostral to the facial motor nucleus in the region commonly referred to as the superior salivatory nucleus.

Use of oral creatine as an ergogenic aid for increased sports performance: perceptions of adolescent athletes

BACKGROUND

Competitive athletes, including adolescents, seek ways to gain advantage over competitors. One ergogenic aid is creatine, a naturally occurring nitrogen compound found primarily in skeletal muscle. Increasing creatine levels may prolong skeletal muscle activity, enhancing work output.

METHODS

A questionnaire assessing awareness and use of creatine supplementation was completed by 674 athletes from 11 high schools. Data were statistically analyzed to determine variation among groups.

RESULTS

Of those surveyed, 75% had knowledge of creatine supplements, and 16% used creatine to enhance athletic performance. Percentage of use increased with age and grade level. Awareness and use were greater among boys than girls. Adverse effects were reported by 26%. Most athletes consumed creatine using a method inconsistent with scientific recommendations.

CONCLUSIONS

Use of creatine by adolescent athletes is significant and inconsistent with optimal dosing. Physicians, athletic trainers, and coaches should disseminate proper information and advise these adolescent athletes.

Comparison of posterior and transforaminal approaches to lumbar interbody fusion

STUDY DESIGN

A study of the transforaminal lumbar interbody fusion and the posterior lumbar interbody fusion techniques was performed.

OBJECTIVES

To describe the transforaminal lumbar interbody fusion technique, and to compare operative data, including blood loss and operative time, with data from posterior lumbar interbody fusion technique.

SUMMARY OF BACKGROUND DATA

The evolution of posterior lumbar fusion combined with anterior interbody fusion has resulted in increased fusion rates as well as improved reductions and stability. The transforaminal lumbar interbody fusion technique pioneered by Harms and Jeszensky offers potential advantages and provides a surgical alternative to more traditional methods.

METHODS

In 13 consecutive months, two spinal surgeons performed 40 transforaminal lumbar interbody fusions and 34 posterior lumbar interbody fusion procedures. Data regarding blood loss, operative times, and length of hospital stay were recorded. These data were analyzed using analysis of variance to show any significant differences between the two techniques. To determine whether differences in measured variables were dependent on patient gender or number of levels fused, epsilon(chi2) analysis was used.

RESULTS

No significant differences were found between transforaminal and posterior lumbar interbody fusions in terms of blood loss, operative time, or duration of hospital stay when a single-level fusion was performed. Significantly less blood loss occurred when a two-level fusion was performed using the transforaminal approach instead of the posterior approach (P < 0.01). Differences in measured variables for the two procedures were independent of patient age, gender, and the number of levels fused. There were no complications with the transforaminal approach, but the posterior approach resulted in multiple complications.

CONCLUSIONS

In this comparison of patients receiving transforaminal lumbar interbody fusion versus posterior lumbar interbody fusion, no complications occurred with the transforaminal approach, whereas multiple complications were associated with the posterior approach. Similar operative times, blood loss, and duration of hospital stay were obtained in single-level fusions, but significantly less blood loss occurred with the transforaminal lumbar interbody approach in two-level fusions. The transforaminal procedure preserves the interspinous ligaments of the lumbar spine and preserves the contralateral laminar surface as an additional surface for bone graft. It may be performed at all lumbar levels because it avoids significant retraction of the dura and conus medullaris.

Intraoperative loosening of Bagby and Kuslich cages during anterior lumbar interbody fusion

The Bagby and Kuslich (BAK) interbody fusion system has been shown to be a safe and effective method for obtaining solid fusion while maintaining lumbar lordosis. Although postoperative cage loosening has been reported, intraoperative cage loosening has not. The authors describe three cases in which BAK cages became loosened during operation. After the first BAK cage was inserted, it appeared to be well positioned and firmly seated; after placement of the second cage, however, the first cage was loose. Each of these cages was replaced without incident and appeared well placed on follow-up. It is crucial for the surgeon to verify that all cages are firmly seated before closure. This may reduce the incidence of postoperative cage migration.

Computed three-dimensional structures for the ras-binding domain of the raf-p74 protein complexed with ras-p21 and with its suppressor protein, rap-1A

The three-dimensional structures of the ras-p21 protein and its protein inhibitor, rap-1A, have been computed bound to the ras-binding domain, RBD (residues 55-131), of the raf-p74 protein, a critical target protein of ras-p21 in the ras-induced mitogenic signal transduction pathway. The coordinates of RBD have been reconstructed from the stereoview of an X-ray crystal structure of this domain bound to rap-1A and have been subjected to energy minimization. The energy-minimized structures of both ras-p21 and rap-1A, obtained in previous studies, have been docked against RBD, using the stereo figure of the RBD-rap-1A complex, based on a six-step procedure. The final energy-minimized structure of rap-1A-RBD is identical to the X-ray crystal structure. Comparison of the ras-p21- and rap-1A-RBD complexes reveals differences in the structures of effector domains of ras-p21 and rap-1a, including residues 32-47, a domain that directly interacts with RBD, 60-66, 96-110, involved in the interaction of ras-p21 with jun kinase (JNK) and jun protein, and 115-126, involved in the interaction of p21 with JNK. The structure of the RBD remained the same in both complexes with the exception of small deviations in its beta-2 binding loop (residues 63-71) and residues 89-91, also involved in binding to rap-1A. The results suggest that the binding of these two proteins to RBD may allow them to interact with other cellular target proteins such as JNK and jun.

Purification, pharmacological characterization and photoaffinity labeling of sigma receptors from rat and bovine brain

The sigma receptor/binding site, found in the brain and periphery, binds haloperidol, (+)-benzomorphans, N-propyl-3-(3-hydroxyphenyl)-piperidine (3-PPP) and certain atypical neuroleptics with high affinity. We have succeeded in ca. 6,000-fold purification of protein(s) from rat and bovine cerebellum which display pharmacology characteristic of the sigma receptor. This purification was achieved by affinity chromatography using a Sepharose gel linked to a new high-affinity ligand, (S)-3-(3-methoxyphenyl)-3'-oxo-3'-phenyl-N-propylpiperidine, an analog of (S)-3-PPP. Elution of the affinity column with haloperidol afforded material which, after reconstitution into bimolecular lipid vesicles, was pharmacologically characterized by specific radioligand binding assays using [3H]haloperidol combined with competitive displacement using appropriate selective ligands. Comparison of the relative rank orders of potency of the ligands in these selective sigma receptor assays corresponded well with values obtained with tissue homogenates. The observed enantioselectivity for the binding of SKF-10,047 and cyclazocine suggests that the material purified corresponds to the sigma 1 receptor subtype. SDS-PAGE indicated that the purified material consisted of two bands of approximate molecular masses 65 and 63 kilodaltons. Photoaffinity labeling of the affinity-purified receptor with [3H]azido-DTG led to incorporation of the label into material of molecular mass 50-70 kDa, by slicing of SDS gels, while similar photolabeling of crude cerebellar homogenates led to exclusive labeling of a 29 kDa polypeptide, as found previously using other tissues. Molecular sizing under non-denaturing conditions indicated the photolabeled species is a labile large receptor complex of mass ca. 300-500 kDa which gradually breaks down upon standing at -80 degrees C into the lower mass (50-70 kDa) material. The sigma receptor ligand binding subunit, which appears to be of the sigma 1 subtype, appears to be contained within the 29 kDa polypeptide, which may be a subunit of the 63-65 kDa protein, which in turn appears to be a component of a much larger receptor complex. It further appears that the 29 kDa polypeptide is readily dissociable from a larger photolabeled sigma receptor complex in tissue homogenates, but does not dissociate from the photolabeled affinity-purified CHAPS-solubilized sigma receptor.

Purification and partial amino acid sequence of a 28 kDa cyclophilin-like component of the rat liver sigma receptor

The sigma (sigma) receptor, a putative non-opioid receptor site which has been suggested to function as a neuromodulator of dopaminergic and NMDA systems, and is found in brain, liver and many other tissues, has been purified > 560-fold from a detergent-solubilized rat liver membrane preparation by affinity chromatography, using an affinity matrix prepared from an oximino derivative of haloperidol. The affinity column selectively retained principal components of M(r) 28 kDa, 40 kDa and 65 kDa that could be eluted from the column with sigma-selective ligands, specifically dextrallorphan and haloperidol. After dialysis and concentration by ultrafiltration, a loss in density of the 65 kDa component and an increase in the 28 kDa and 40 kDa components was observed. A 15 amino acid N-terminal sequence was obtained for the 28 kDa protein which is identical to the N-terminal sequence of the 17 kDa rat cyclophilin A, a cytosolic protein, suggesting that a critical component of the rat liver sigma receptor may be a cyclophilin. These results support the suggestion that sigma receptors are a key link between the central nervous system and the immune system.

Molecular dynamics of the H-ras gene-encoded p21 protein; identification of flexible regions and possible effector domains

We previously reported a complete computer-based three-dimensional structure for residues 1-171 of the Gly 12-containing ras-gene-encoded p21 protein complexed with GDP. This structure was subsequently shown to closely agree with a high-resolution x-ray crystallographic structure of p21. In this communication, we report a molecular dynamics stimulation of the modelled structure in an explicit shell of water molecules to identify domains within the protein that are unusually flexible. These domains represent regions which are most likely to undergo important conformational changes when the protein is activated by binding to GTP or by oncogenic amino acid substitutions such as Val for Gly 12. The starting structure was surrounded with water molecules, temperature-equilibrated and then followed over a 100 ps trajectory during which time the energy converged after about 50 ps. Regions of the protein that were found to have the largest coordinate fluctuations involved residues 12-16, 30-35, 40-52, 60-73, 85-89, 101-109, 119-123, and 127-131. Many of these sequences with high flexibility have been implicated in the functioning of this protein. Since the overall largest fluctuations were observed for residues 101-106 and 119-123, p21 peptides containing these residues (96-110 and 115-126) were synthesized and were found to inhibit strongly the effects of oncogenic p21 protein in an oocyte maturation assay. These results indicate that the flexible p21 sequences may constitute critical functional domains of the activated protein and that this general approach may be useful for identification of important functional domains in proteins.

N-(1-arylpropionyl)-4-aryltetrahydropyridines, a new class of high-affinity selective sigma receptor ligands

A series of N-(1-arylpropionyl)-4-aryl-1,2,3,6-tetrahydropyridines, prepared by simple Mannich condensations, have been found by radioligand binding assays to have moderate to high affinity (IC50 0.5-500 nM) for bovine cerebellar sigma receptor/binding sites and no measurable affinity (IC50 > 5000 nM) for bovine striatal D2 receptors. The most active of these compounds rival in potency the most active sigma ligands previously reported. Three of these sigma-active compounds were screened for pharmacological activity under the NIMH-NovaScreen program and showed moderate affinity only for D2 and 5-HT2 receptors among the 40 sites assayed. Since these N-(1-arylpropionyl)-4-aryltetrahydropyridines are structurally related to other potent sigma receptor ligands, in particular haloperidol and 4-phenylpiperidines, these data provide insights into the nature of the essential pharmacophore of the sigma receptor. The selective affinity of these materials for sigma receptors indicates they have potential as prototypes of novel psychotherapeutic medicinal agents, particularly as antipsychotic drugs which would be devoid of debilitating side effects associated with blockade of D2 receptors.

A comparison of techniques for introducing macromolecules into living cells

Flow cytometry has been used to evaluate several techniques for introducing macromolecules into large numbers of living cells. One technique is cell fusion with red blood cell ghosts loaded with a fluorescent reporter molecule (RBCF). The second technique, termed osmotic lysis of pinosomes (OLP), involves a brief exposure of cells to a hypertonic solution containing the reporter molecule; subsequently, a hypotonic media is added which lyses the pinosomes formed during the hypertonic treatment. A third technique, scrape loading (SL), involves the creation of transient holes in the cell membrane through the application of mechanical forces, which allows for the passage of reporter molecules into cells. A comparison of these techniques is presented here. OLP appears to offer several advantages: It is a simple procedure, virtually all cells are fluorescently labelled, and it is capable of loading larger amounts of material more uniformly into cells while maintaining excellent viability.

Enkephalin is a competitive antagonist of cholecystokinin in the gastrointestinal tract, as predicted from prior conformational analysis

Prior calculations based on ECEPP (Empirical Conformational Energies for Peptides Program) of the low energy minima for cholecystokinin (CCK) and Met-enkephalin have demonstrated that significant structural features of these two peptides are identical. This result suggested the possibility that Met-enkephalin, as well as other enkephalin analogues of similar structure, could associate with receptors for CCK. To test this theoretical result, we examined the ability of Met-enkephalin and its analogues to bind to peripheral CCK receptors in the rat gastrointestinal tract; in particular, we measured the ability of the opiate peptide to inhibit the effects of CCK in a physiological assay system which we have previously characterized: CCK-induced contraction of the isolated rat pyloric sphincter. We find that Met-enkephalin is an antagonist of the CCK-8-induced contraction, with a IC50 of 110 nM. Furthermore, antibodies against CCK were found to cross-react with Met-enkephalin and its analogues in a manner which suggests a distinct structure-activity relationship. These experimental results strongly support the theoretical results of conformational analysis showing structural similarity between enkephalin and CCK. They further suggest that enkephalins could modulate the response of CCK systems under physiological conditions.

Evidence that oocyte maturation induced by an oncogenic ras-p21 protein and insulin is mediated by overlapping yet distinct mechanisms

We have recently shown that a peptide (residues 35-47) from a functional region of the ras p21 protein, thought to be involved in the binding of p21 to GTPase activating protein, the antibiotic azatyrosine, known to induce the ras-recision gene, and the selective protein kinase C inhibitor, CGP 41,251, all inhibit oncogenic p21 protein-induced maturation of oocytes in a dose-dependent manner. We now show that these three agents only partially inhibit insulin-induced oocyte maturation, known to be dependent on activation of cellular p21 protein. On the other hand, the anti-p21 protein antibody Y13-259 completely inhibits both insulin- and oncogenic p21 protein-induced maturation as does a tetrapeptide, CVIM, known to block the enzyme farnesyl transferase which covalently attaches the farnesyl moiety to the p21 protein allowing it to attach to the cell membrane. Our results suggest that while the oncogenic and insulin-activated normal p21 proteins share certain elements of their signal transduction pathways in common, these pathways diverge and allow for selective inhibition of the oncogenic pathway.

Evidence that the ras oncogene-encoded p21 protein induces oocyte maturation via activation of protein kinase C

The ras oncogene-encoded p21 protein is known to induce cell maturation of Xenopus laevis oocytes and malignant transformation of NIH 3T3 mouse fibroblasts. The pathways involved in oocytes and NIH 3T3 cells appear to be similar to one another. For example, in both cases, the ras p21-induced cellular events involve increased intracellular levels of the second messengers diacylglycerol and inositol phosphates, the former of which activates protein kinase C (PKC). To investigate the pathway of ras-induced oocyte maturation, we have explored the relationship between p21 protein and PKC. We show that the maturation signal from oncogenic p21 microinjected into Xenopus oocytes is completely blocked by the relatively specific PKC inhibitor CGP 41251, a staurosporine analogue that selectively inhibits PKC, but not by an inactive analogue of staurosporine, CGP 42700. Microinjection of purified PKC or of phorbol ester induces maturation of oocytes. PKC-induced maturation is inhibited by CGP 41251 but not by CGP 42700. Maturation induced by microinjected PKC is also not inhibited by two specific anti-p21 agents, the inactivating anti-p21 monoclonal antibody Y13-259 and the amino acid derivative azatyrosine. Both of these agents block p21-induced cell maturation. These results suggest that ras effects depend upon the action of PKC, whose activation is an event that occurs downstream of p21 in the maturation signal pathway.

Peripheral factors in the mediation of cholecystokinin-induced satiety as assessed by comparative potencies of cholecystokinin antagonists

Cholecystokinin COOH-terminal octapeptide (CCK-8) produces a satiating effect in the rat and other animals upon peripheral administration. Although it has been demonstrated that the receptors which mediate this action are located in the periphery and are of the CCK-A subtype, their anatomical location has not been firmly established. A dense population of CCK receptors in the pyloric sphincter has been suggested as a candidate. We here quantify the potency of several CCK antagonists to inhibit the contractile effect of CCK-8 on the rat pyloric sphincter in vitro. The potent and selective antagonist MK-329 has a Schild pK of 8.85; the less potent but selective antagonist lorglumide (CR-1409) a pK of 6.37; the related antagonist phenoxyacetylproglumide (phi oAc proglumide) a pK of 5.1; and the weak parent compound proglumide a pK of about 3.3. These data can be compared with the potencies of these compounds to inhibit the actions of CCK-8 to produce satiety in the rat; this comparison supports the contention that CCK receptors of the rat pyloric sphincter could in part mediate the satiety effect produced by exogenous CCK-8.

A peptide from the GAP-binding domain of the ras-p21 protein as well as azatyrosine block ras-induced maturation of Xenopus oocytes

The ras-oncogene-encoded p21 protein is known to produce malignant transformation of NIH 3T3 cells as well as maturation of Xenopus oocytes when microinjected into these cells. p21 protein is known to bind a GTPase activating protein (GAP) intracellularly; residues 32-45 have been implicated in interacting with GAP. We demonstrate here that a peptide corresponding to residues 35-47 of p21 as well as the antibiotic azatyrosine inhibit the ras-induced maturation of Xenopus oocytes in a dose-related manner upon microinjection. We have previously shown that this p21 peptide and azatyrosine could inhibit the effects of p21 protein on cell transformation and pinocytosis in NIH 3T3 cells. In the present study, in which we have extended these results to the oocyte system, we also demonstrate that both partially inhibit insulin-induced oocyte maturation, a process which is thought to involve activation of endogenous p21 protein; on the other hand, both agents fail to inhibit oocyte maturation induced by progesterone, which is known not to act through p21 protein activation. Control studies with other peptides and tyrosine analogues support the selective nature of these events. These results suggest that both the p21-related peptide and azatyrosine have potent anti-ras effects intracellularly.

A peptide from the GAP-binding domain of the ras-p21 protein and azatyrosine block ras-induced maturation of Xenopus oocytes

The ras-oncogene-encoded p21 protein causes malignant transformation of NIH 3T3 cells and maturation of Xenopus oocytes when microinjected into these cells. P21 is known to interact with GTPase activating protein (GAP) intracellularly. Residues 32-45 of p21 have been implicated in interacting with GAP. In a previous study, we demonstrated that a synthetic peptide containing residues 35-47 from the GAP-binding region of p21 could block in vivo the effects of oncogenic p21 protein. It has also been found that an antibiotic, azatyrosine, blocks ras-initiated cell transformation. We now demonstrate that both of these agents inhibit the ras-p21 protein-induced maturation of Xenopus oocytes in a dose-related manner when microinjected into oocytes. The effects of each of these agents is specific. Both agents block insulin-induced maturation of oocytes, a process which is known to involve activation of endogenous normal p21 protein. On the other hand, neither agent inhibited oocyte maturation induced by progesterone, which is known to initiate oocyte maturation by ras-independent pathways. The inhibitory effects of the peptide were not mimicked by a control peptide from the CD4 receptor protein. Furthermore, the effect of azatyrosine was not mimicked by L-tyrosine. These results suggest that both the peptide and azatyrosine have potent anti-ras effects intracellularly.

Activity of hippocampal extract on development of [3H]5-HT high-affinity uptake in dissociated microcultures

Specific and localized lesions of the 5-HT fibers in the hippocampus induce homotypic collateral sprouting and enhance serotonergic fiber outgrowth from adult neurons and transplanted fetal tissue. In this study, hippocampal extracts were prepared and applied to primary cultures of fetal serotonergic neurons. The effects of plating density and serum additives were examined. The growth of the serotonergic neurons in the rostral brainstem dissociated cultures were estimated by measuring the specific uptake of [3H]5-HT. The results indicate the presence of a trypsin-sensitive factor which is active when prepared fresh at dilutions up to 1/10,000. The factor is higher in hippocampus than cerebellum. Young male tissue contained more activity than either female or aged hippocampus. Although both positive and negative effects are described, higher dilutions of factor (1/1,000) were generally stimulatory in high density cultures while lower dilutions (1/10) were inhibitory in low density cultures. Specific removal of 5-HT hippocampal afferents with fornix-fimbria microinjections of 5,7-dihydroxytryptamine resulted in an initial loss of activity (2 days and 2 weeks) followed by an enhanced activity (2 months) compared to normal hippocampal extract. Several possibilities are discussed as to the identity of the serotonergic growth factor from hippocampal supernatant.

Comparison of the predicted structure for the activated form of the P21 protein with the X-ray crystal structure

The predicted conformation and position of the central transforming region (residues 55-67) of the p21 protein are compared with the conformation and position of this segment in a recently determined X-ray crystal structure of residues 1-166 of this protein in the activated state bound to a nonhydrolyzable GTP derivative. We previously predicted that this segment of the protein would adopt a roughly extended conformation from Ile 55-Thr 58, a reverse turn at Ala 59-Gln 61, followed by an alpha-helix from Glu 62-Met 67. We further predicted that this region of the activated protein occupies a position that is virtually identical to corresponding regions in the homologous purine nucleotide-binding proteins, bacterial elongation factor (EF-tu), and adenylate kinase (ADK). We find that there is a close correspondence between the conformation and position of our predicted structure and those found in the X-ray crystal structure. A mechanism for activation of the protein is proposed and is corroborated by X-ray crystallographic data.

Octapeptide segments from the amino terminus of glycophorin A contain the antigenic determinants of the M and N blood groups systems

Human red blood cells with phenotype N/N and M/M were tested in an agglutination assay with anti-N and anti-M antibodies, respectively. After incubation of the synthesized octapeptide (Leu-Ser-Thr-Thr-Glu-Val-Ala-Met) from the N-amino terminus of glycophorin A, with anti-N antibody, there was significant inhibition of the agglutination of the N-positive cells. There was also inhibition of the agglutination of the M-positive cells with anti-M antibody by the synthesized octapeptide (Ser-Ser-Thr-Thr-Gly-Val-Ala-Met) from the M-amino terminus of glycophorin A. There was no inhibition, however, of the agglutination of M-positive cells with anti-M antibodies by the N-amino terminal octapeptide. Likewise, the M-amino terminal octapeptide did not inhibit agglutination of N-positive cells with anti-N. Because the synthesized octapeptides contained no carbohydrate, the anti-N and anti-M specificity appears to be determined principally by the peptides themselves. Further studies with the use of chimeric peptides indicate that the amino terminal amino acid leucine of N-glycophorin A is a primary determinant of the N antigen, whereas the amino terminal serine of M-glycophorin A is a primary determinant for the M antigen.

Conformations of the central transforming region (Ile 55-Met 67) of the p21 protein and their relationship to activation of the protein

The GTP-binding p21 protein, encoded by the ras-oncogene, becomes transforming if amino acid substitutions are made at critical positions in the polypeptide chain, e.g., at Gly 12, Gly 13, Ala 59, Gln 61 and Glu 63. Most of these substitutions occur in two phosphate-binding loop regions, Tyr 4-Thr 20, herein designated as segment 1, and Ile 55-Met 67, herein designated, as segment 2. These two segments are homologous to two corresponding regions in the two purine nucleotide binding proteins, bacterial elongation factor (EF-tu) (Val 12-Thr 28 corresponds to segment 1; His 78-Ile 92 corresponds to segment 2) and adenylate kinase (ADK) (Lys 9-Cys 25 corresponds to segment 1 and Tyr 95-Arg 107 corresponds to segment 2). We find that the conformations of the segment 1 region in the p21 protein, EF-tu and ADK are similar to one another and that the conformation of the segment 2 region of EF-tu is superimposable on that of segment 2 of ADK. Furthermore, the relative position of the two segments in EF-tu is strikingly similar to that of the two segments in ADK. In the originally proposed X-ray structure for the p21 protein, the conformation of segment 2 in the p21 protein is not similar to that found for the other two proteins, and its disposition relative to segment 1 and the remainder of the protein is also different from that observed for the other two proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparisons between the three-dimensional structures of the chemotactic protein CheY and the normal Gly 12-p21 protein

The three-dimensional structure of a chemotactic protein CheY from Salmonella typhimurium has recently been determined by X-ray crystallography. The structure of this small protein, containing 129 amino acid residues, shows a domain consisting of a central beta-pleated sheet surrounded on both sides by alpha-helices. We have examined the sequence and the arrangement of the structural domains of the CheY protein and have compared them with other nucleotide binding protein sequences and structures. We find that the CheY protein has significant sequence homology to the ras-gene encoded p21 protein. In addition, the structural domains of the two proteins are arranged in a fundamentally similar manner, including the phosphate-binding site (both proteins bind phosphate-containing ligands). The striking similarity in the arrangement of the structural domains of the two proteins suggests that both may serve similar functions as signal transducers.

MDMA (ecstasy) effects on cultured serotonergic neurons: evidence for Ca2(+)-dependent toxicity linked to release

Animal studies have established a correlation between release of 5-hydroxytryptamine (5-HT) and the long-term reduction of 5-HT (toxicity) by 3,4-methylenedioxymethamphetamine (MDMA) with the S(+) enantiomer being more active than the R(-). Using a microculture system of fetal raphe neurons, the enantiomers of MDMA were tested to determine if a similar difference in potency existed. The results showed that the development of the uptake capacity of [3H]5-HT in 4-day cultures was half-maximally inhibited by a single application at time of plating of 5 X 10(-6) M S(+)-MDMA and 5 X 10(-5) M R(-)-MDMA. In order to determine if the Ca2(+)-independent release (chemically induced through the transporter protein and inhibited by reuptake blockers) or the Ca2(+)-dependent release (K(+)-induced and inhibited by presynaptic receptors) contributed to the toxicity, fluoxetine and D1 and alpha 2 agonists were studied. The results showed that both forms of release were involved in the loss of [3H]5-HT uptake capacity, with the direct MDMA-induced Ca2(+)-independent (fluoxetine-sensitive) release being the first step. Evidence from binding studies indicates that MDMA has a micromolar affinity for the 5-HT2 receptor, and our studies in culture showed that ketanserin, a specific 5-HT2 antagonist, was effective at attenuating the effects of S(+)-MDMA on the development of the [3H]5-HT uptake capacity by the cultured raphe neurons. The 5-HT2 receptor is linked to increased intracellular Ca2+ through a second messenger phosphatidylinositol (PI)-hydrolysis mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of an intracellular protein that specifically interacts with photoaffinity-labeled oncogenic p21 protein

An oncogenic 21-kDa (p21) protein (Harvey RAS protein with Val-12) has been covalently modified with a functional reagent that contains a photoactivatable aromatic azide group. This modified p21 protein has been introduced quantitatively into NIH 3T3 cells using an erythrocyte-mediated fusion technique. The introduced p21 protein was capable of inducing enhanced pinocytosis and DNA synthesis in the recipient cells. To identify the putative intracellular protein(s) that specifically interact with the modified p21 protein, the cells were pulsed with [35S]methionine at selected times after fusion and then UV-irradiated to activate the azide group. The resulting nitrene covalently binds to amino acid residues in adjacent proteins, thus linking the p21 protein to these proteins. The cells were then lysed, and the lysate was immunoprecipitated with the anti-p21 monoclonal antibody Y13-259. The immunoprecipitate was analyzed by SDS/PAGE to identify p21-protein complexes. By using this technique, we found that three protein complexes of 51, 64, and 82 kDa were labeled specifically and reproducibly. The most prominent band is the 64-kDa protein complex that shows a time-dependent rise and fall, peaking within a 5-hr period after introduction of the p21 protein into the cells. These studies provide evidence that in vitro the p21 protein becomes associated with a protein whose mass is about 43 kDa. We suggest that the formation of this complex may play a role in mediating early events involved with cell transformation induced by RAS oncogenes.

Comparison of the computed structures for the phosphate-binding loop of the p21 protein containing the oncogenic site Gly 12 with the X-ray crystallographic structures for this region in the p21 protein and EFtu. A model for the structure of the p21 protein in its oncogenic form

The GTP-binding p21 protein encoded by the ras-oncogene can be activated to cause malignant transformation of cells by substitution of a single amino acid at critical positions along the polypeptide chain. Substitution of any non-cyclic L-amino acid for Gly 12 in the normal protein results in a transforming protein. This substitution occurs in a hydrophobic sequence (residues 6-15) which is known to be involved in binding the phosphate moities of GTP (and GDP). We find, using conformational energy calculations, that the 6-15 segment of the normal protein (with Gly 12) adopts structures that contain a bend at residues 11 and 12 with the Gly in the D* conformation, not allowed energetically for L-amino acids. Substitution of non-cyclic L-amino acids for Gly 12 results in shifting this bend to residues 12 and 13. We show that many computed structures for the Gly 12-containing phosphate binding loop, segment 9-15, are superimposable on the corresponding segment of the recently determined X-ray crystallographic structure for residues 1-171 of the p21 protein. All such structures contain bends at residues 11 and 12 and most of these contain Gly 12 in the C* or D* conformational state. Other computed conformations for the 9-15 segment were superimposable on the structure of the corresponding 18-23 segment of EFtu, the bacterial chain elongation factor having structural similarities to the p21 protein in the phosphate-binding regions. This segment contains a Val residue where a Gly occurs in the p21 protein. As previously predicted, all of these superimposable conformations contain a bend at positions 12 and 13, not 11 and 12. If these structures that are superimposable on EFtu are introduced into the p21 protein structure, bad contacts occur between the sidechain of the residue (here Val) at position 12 and another phosphate binding loop region around position 61. These bad contacts between the two segments can be removed by changing the conformation of the 61 region in the p21 protein to the corresponding position of the homologous region in EFtu. In this new conformation, a large site becomes available for the binding of phosphate residues. In addition, such phenomena as autophosphorylation of the p21 protein by GTP can be explained with this new model structure for the activated protein which cannot be explained by the structure for the non-activated protein.

Comparative X-ray crystallographic evidence for a beta-bend conformation as the active structure for peptide T in T4 receptor recognition

A sequence similarity has been found between two segments of endothiapepsin (acid proteinase, 2APE), bovine pancreatic ribonuclease A, and peptide T, a segment of the gp120 protein of human immune deficiency virus (HIV), which has been implicated in blocking viral attachment to the T4 receptor. The two similar sequences of the acid proteinase enzyme are Leu-Ile-Asp-Ser-Ser-Ala-Tyr-Thr (residues 169-176) and Tyr-Thr-Gly-Ser-Leu-Asn-Tyr-Thr (residues 175-182). Since the X-ray crystallographic structures of the acid proteinase and ribonuclease are known, it has been possible to determine whether the three-dimensional structures of the segments are similar. Portions of both the segments of acid proteinase are directly superimposable on the structure of the RNase A 19-26 segment. The fact that the three similar sequences from two completely unrelated proteins give rise to almost identical structures raises the possibility that these segments may be involved in nucleating the folding of these proteins. In addition, this provides further support for the concept that the octapeptide sequence of peptide T of HIV, which is also similar in sequence to the 19-26 sequence of RNase A, is also structurally similar to these residues, which adopt a beta-bend conformation. Furthermore, comparison of similarities and differences in the structure of these similar sequences provides an explanation for alterations in the biological activity of various truncated or substituted derivatives of peptide T and additional confirmation of the structural requirements for peptide T in T4-receptor recognition.

Conformation of the metastasis-inhibiting laminin pentapeptide

The binding of cancer cells to the basement membrane glycoprotein laminin appears to be a critical step in the metastatic process. This binding can be inhibited competitively by a specific pentapeptide sequence (Tyr-Ile-Gly-Ser-Arg) of the laminin B1 chain, and this peptide can prevent metastasis formation in vivo. However, other similar pentapeptide sequences (e.g., Tyr-Ile-Gly-Ser-Glu) have been found to be much less active in metastasis inhibition, raising the possibility that such amino acid substitutions produce structural changes responsible for altering binding to the laminin receptor. In this study, conformational energy analysis has been used to determine the three-dimensional structures of these peptides. The results indicate that the substitution of Glu for the terminal Arg produces a significant conformational change in the peptide backbone at the middle Gly residue. These results have important implications for the design of drugs that may be useful in preventing metastasis formation and tumor spread.

Two proglumide analogues are equipotent antagonists of the inhibition of food intake by CCK-8

The reduction in food intake produced by exogenous CCK-8 (8 micrograms.kg-1, IP) in 18 hr food-deprived rats was significantly reversed by either of two proglumide analogues at doses of 0.44 and 4.4 microM.kg-1. The two glutamic acid derivatives tested were CR-1409 [N-(3,4-dichlorobenzoyl)-L-glutamic acid-1-di-n-pentylamide], effective at doses of 0.2 and 2.0 mg.kg-1, IP, and PGDPA [N-(phenoxyacetyl)-L-glutamic acid-1-di-n-propylamide], effective at the equimolar doses of 0.16 and 1.6 mg.kg-1, IP, as well as at 16 mg.kg-1 (44 microM.kg-1). By comparison, proglumide reversed the inhibition of food intake by CCK-8 at 160 mg.kg-1 (470 microM.kg-1), but not at 16 mg.kg-1 (47 microM.kg-1). At the 0.44 microM.kg-1 dose which antagonized CCK-8-induced satiety, neither PGDPA nor CR-1409 reduced the inhibition of food intake induced by bombesin, supporting the behavioral specificity of these CCK antagonists. Previous in vitro studies have shown that CR-1409 was approximately 4000-fold more potent than proglumide and PGDPA was 100-fold more potent than proglumide as antagonists of CCK-8-induced amylase secretion and binding in pancreatic acinar cells. Here, we found no potency difference between PGDPA and CR-1409; each was more than 1000-fold more potent than proglumide as an antagonist of the inhibition of food intake produced by CCK-8. This nonparallelism between the potencies of these antagonists at CCK receptors located upon pancreatic acinar cells and at CCK receptors involved in CCK-8-induced satiety suggests that the two receptor populations differ pharmacologically.

Conformational analysis of possible biologically active (receptor-bound) conformations of peptides derived from cholecystokinin, cerulein and little gastrin and the opiate peptide, Met-enkephalin

Possible biologically active (receptor-bound) conformations of peptides derived from cholecystokinin (CCK) have been deduced using conformational analysis combined with comparative studies of their biological specificities. Two peptides, the completely active carboxyl terminal heptapeptide from CCK (CCK-7), whose sequence is Tyr-Met-Gly-Trp-Met-Asp-Phe-NH2, and the carboxyl terminal heptapeptide from cerulein (CER-7) which has the same sequence as for CCK-7 except for replacement of Met 2 with a Thr 2, both stimulate peripheral receptors in gall bladder, pancreas, and pylorus in the gastrointestinal system. In contrast, two other very similar peptides, the last four residues of CCK (CCK-4) whose sequence is Trp-Met-Asp-Phe-NH2, and the carboxyl terminal hexapeptide of little gastrin (LGA-6, Tyr-Gly-Trp-Met-Asp-Phe-NH2, i.e., residue 2 deleted relative to CCK-7 and CER-7 sequences), interact specifically with gastrin receptors and not at all or very weakly with peripheral receptors. All of these peptides react with CCK receptors in the central nervous system, especially in forebrain. The results in the GI tract suggest that the peptides active on peripheral receptors adopt structures that are significantly different from those of the peptides that interact with gastrin receptors. We have generated all of the many low energy conformations for each of these peptides. By retaining only the conformations that are the same for peptides within the same group and then rejecting those resulting conformations that are the same for the peptides in the two different groups, we can greatly reduce the possible active conformations for the peptides within each class.(ABSTRACT TRUNCATED AT 250 WORDS)

On the biologically active structures of cholecystokinin, little gastrin, and enkephalin in the gastrointestinal system

The biologically active conformations of a series of four peptides [four cholecystokinin (CCK)-related peptides and enkephalin] in their interactions with gastrointestinal receptors have been deduced using conformational computational analysis. The two peptides that interact exclusively with peripheral-type CCK receptors are the heptapeptide COOH-terminal fragment from CCK (CCK-7) and the analogous sequence from cerulein (CER-7) in which threonine replaces the methionine proximal to the NH2 terminus. The two peptides that interact exclusively with the gastrin receptor in the stomach are the active COOH-terminal fragment of little gastrin and the COOH-terminal tetrapeptide sequence common to all of these peptides, CCK-4. We find that preferred conformations for the peripherally active peptides CCK-7 and CER-7 are principally beta-bends, whereas little gastrin and CCK-4 are fundamentally helical. In the class of lowest energy structures for both CCK-7 and CER-7, the aromatic rings of the tyrosine and phenylalanine lie close to one another whereas the tryptophan indole ring points in the opposite direction. This structure is superimposable on the structures of a set of rigid indolyl benzodiazepine derivatives that interact with complete specificity and high affinity with peripheral CCK receptors further suggesting that the computed beta-bends are the biologically active conformation. The biologically active conformation for CCK-4 and the little gastrin hexapeptide has also been deduced. By excluding conformations common to CCK-7 and CCK-4, which do not bond to each other's receptors, and then by selecting conformations in common to CCK-4 and the gastrin-related hexapeptide, which do bind to each other's receptors, we deduce that the biologically active conformation at the gastrin receptor is partly helical and one in which the indole of tryptophan and the aromatic ring of phenylalanine are close to one another while the methionine and aspartic acid side chains point in the opposite direction. These major differences in preferred structures between the common CCK-7/CER-7 peptides and the common CCK-4/little gastrin peptides explain the mutually exclusive activities of these two sets of peptides. We have observed that [Met]enkephalin strongly antagonizes the action of the naturally occurring peripherally active CCK-8 (CCK-7 with an NH2-terminal aspartic acid residue added). The computed lowest energy structures for this opiate peptide closely resemble key features of the computed CCK-7/CER-7 structure, further supporting the proposed structure.

A strong homology exists between the active T-cell binding gp120 octapeptide of human immunodeficiency virus and the subtilisin cleavage peptide of bovine ribonuclease A

A homology has been found between an octapeptide involved in attachment of the human immunodeficiency virus to helper/inducer T cells and an octapeptide segment of bovine pancreatic ribonuclease A. This segment (residues 19-26) contains the sites for subtilisin cleavage of this enzyme into the S-peptide and S-protein. From the X-ray crystal structure of ribonuclease, this sequence is known to be exposed to solvent and interacts little with the rest of the protein. A structure for the human immunodeficiency virus attachment peptide can be deduced from this homology, as a well-defined structure has been determined for this sequence in ribonuclease. This can be readily accomplished using previously developed computer methods based upon conformational energy calculations. The calculated structure for human immunodeficiency virus peptide is identical to the ribonuclease segment (19-26) in backbone conformation. It is stabilized by internal interactions of nonpolar residues, and by exposure of polar hydroxyl groups. The results suggest that the T-cell human immunodeficiency virus receptor may be hydrophilic in nature and that conservation of the sequence in two presumably functionally unrelated proteins is related to the need for conservation of exposed structure.

Pharmacological examination of cholecystokinin (CCK-8)-induced contractile activity in the rat isolated pylorus

The actions of cholecystokinin (CCK) in the production of a satiety-like state have been suggested to be mediated via receptors for CCK which are located in the pylorus. We investigated the actions of CCK and other pharmacological agents upon the isolated rat pylorus in vitro. We used the change in isometric tension of the tissue preparation (contraction amplitude) as the measure of the effects of the pharmacological agents. Cholecystokinin COOH-terminal octapeptide (CCK-8) was observed to elicit contraction in a dose-dependent manner, with the half-maximal dose (ED50) in the vicinity of 1 nM. Rapid desensitization to CCK was observed. The contraction amplitude was atropine-independent, and was not significantly antagonized by a wide variety of other pharmacological agents. The Na+-channel blocker tetrodotoxin was without effect upon contractile amplitude, as was the K+-channel blocker 4-aminopyridine, except at very high concentrations. Neurotensin, bombesin, and the substance P and bombesin antagonist spantide all elicited contraction in the isolated tissue; neurotensin had a similar potency to CCK-8 and bombesin was 10-15-fold less potent than CCK-8. Unsulfated CCK-8 was at least 170-fold less potent than sulfated CCK-8 and tetragastrin was at least 500-fold less potent than CCK-8. These results suggest that pyloric CCK receptors, which appear to have a pharmacological profile typical of peripheral CCK receptors, may have a physiological role in the peptidergic control of gastric emptying in the rat.

Structural features of various proglumide-related cholecystokinin receptor antagonists

Thirteen proglumide derivatives that varied in the length of the di-n-alkyl group and in the substitutions on the benzoyl moiety were tested for their ability to interact with guinea pig pancreatic cholecystokinin (CCK) receptors. Each derivative was more potent than proglumide. There was a close correlation between their abilities to inhibit CCK-stimulated amylase release and to inhibit binding of 125I-CCK. For the di-n-alkyl derivatives the relative potency was n-pentyl greater than n-hexyl greater than n-butyl greater than n-propyl. For the benzoyl moiety, adding two electron-withdrawing groups increased potency more than adding a single electron-withdrawing group or adding electron-donating groups. The 3,4-dichloro-di-n-pentyl derivative of proglumide was 1,300 times more potent than proglumide, and its action was specific, competitive, and it functioned as a CCK receptor antagonist in rat, mouse, and guinea pig pancreas. For all proglumide derivatives there was a good correlation (r = 0.84, P less than 0.001) between their abilities to inhibit CCK-stimulated amylase release and that previously reported for their abilities to inhibit CCK-induced gallbladder contraction. However, certain proglumide derivatives had a much higher affinity for the pancreatic CCK receptor than for the CCK receptor mediating gallbladder contraction. For other proglumide derivatives the pattern was reversed. These results demonstrate that both the di-n-alkyl group and the substitution on the benzoyl moiety of proglumide are equally important determinants of affinity and that derivatives such as the di-n-pentyl 3,4-dichloro analogue can be produced that are 1,300 times more potent than proglumide.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the use of a novel affinity matrix, sepharose amine-succinyl-amine haloperidol hemisuccinate, ASA-HHS, for purification of canine dopamine (D2) receptor

Haloperidol Hemisuccinate (HHS) was synthesized specifically as a ligand for an affinity chromatography matrix. The affinity chromatography matrix, ASA-HHS was developed which had high affinity and capacity for dopamine D2 receptors in solubilized canine striatal preparations. ASA-HHS also demonstrated nonspecific interaction with the D2 receptor. Two fractions, which bound 3H-spiroperidol specifically, with similar one dimensional SDS-PAGE patterns could be eluted successfully with 20 microM haloperidol in only 30% of the runs. Both fractions represented 300-400 fold purification. Two dimensional IEF-PAGE analysis of one of the fractions demonstrated coelution of beta and gamma actin, alpha and beta tubulin with the 3H-spiroperidol binding sites. The pattern of the proteins eluted from ASA-HHS and the inconsistent recovery of active D2 receptors are discussed.

Lecithin:cholesterol acyltransferase regulation. II. Effect of fluidity of egg phosphatidylcholine vesicles

The regulation of human plasma lecithin:cholesterol acyltransferase (LCAT) by changes in bilayer fluidity of substrate egg phosphatidylcholine (egg PC) unilamellar vesicles was investigated using pyrene excimer fluorescence to measure fluidity. Fluidity was decreased by adding up to 20% cholesterol or increased by adding up to 10% egg 2-lysophosphatidylcholine (lysoPC). The fluidizing effect of lysoPC was suppressed by the addition of cholesterol. LCAT activity with 10% cholesterol vesicles was decreased by adding 5% lysoPC, yet activity with 5% cholesterol vesicles was unaffected by adding 5% lysoPC. This difference may be explained by a balance between the known LCAT inhibitory effect of lysoPC and its ability to increase bilayer fluidity and thereby increase LCAT activity. LCAT esterification of up to 37% of vesicle cholesterol failed to alter the lysoPC/cholesterol balance sufficiently to influence activity in this system. The findings of our studies are in keeping with modulation of LCAT activity by bilayer fluidity, but fluidity changes caused by enzyme action are not sufficient to regulate that activity.

Proglumide analogues: potent cholecystokinin receptor antagonists

Proglumide [N-(benzoyl)-L-glutamic acid-1-di-n-propylamide] is a specific cholecystokinin receptor antagonist. In the present study we synthesized various analogues of proglumide and used pancreatic acini from guinea pig pancreas to examine the abilities of these analogues to function as cholecystokinin receptor antagonists. Each analogue inhibited cholecystokinin octapeptide-stimulated amylase secretion but did not stimulate amylase secretion when present alone. There was a close correlation between the ability of a particular analogue to inhibit the action of cholecystokinin on acinar cell function and its ability to inhibit binding of 125I-cholecystokinin. Structure-function studies demonstrated that neither the dipropylamide nor the benzoyl moieties are essential for inhibiting the action of cholecystokinin but that both groups are important in determining the inhibitory potency. Replacing the dipropylamide group with a hydroxyl group caused a 13-fold decrease in potency. Replacing the benzoyl moiety by an acetyl group caused a 30- to 40-fold decrease in inhibitory potency, whereas replacing the benzoyl moiety by a p-chlorophenoxyacetyl or phenoxyacetyl moiety caused a 75-fold increase in potency. Replacing both the dipropylamide moiety with a hydroxyl group and the benzoyl moiety with a phenoxyacetyl group resulted in a 5-fold decrease in inhibitory potency. Inhibition of cholecystokinin-stimulated amylase release by both the phenoxyacetyl and p-chlorophenoxyacetyl analogues was competitive in nature, fully reversible, and specific for those secretagogues that interact with the cholecystokinin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)