Serine hydroxymethyltransferase from Escherichia coli: purification and properties

Serine hydroxymethyltransferase from Escherichia coli was purified to homogeneity. The enzyme was a homodimer of identical subunits with a molecular weight of 95,000. The amino acid sequence of the amino and carboxy-terminal ends and the amino acid composition of cysteine-containing tryptic peptides were in agreement with the primary structure proposed for this enzyme from the structure of the glyA gene (M. Plamann, L. Stauffer, M. Urbanowski, and G. Stauffer, Nucleic Acids Res. 11:2065-2074, 1983). The enzyme contained no disulfide bonds but had one sulfhydryl group on the surface of the protein. Several sulfhydryl reagents reacted with this exposed group and inactivated the enzyme. Spectra of the enzyme in the presence of substrates and substrate analogs showed that the enzyme formed the same complexes and in similar relative concentrations as previously observed with the cytosolic and mitochondrial rabbit liver isoenzymes. Kinetic studies with substrates showed that the affinity and synergistic binding of the amino acid and folate substrates were similar to those obtained with the rabbit liver isoenzymes. The enzyme catalyzed the cleavage of threonine, allothreonine, and 3-phenylserine to glycine and the corresponding aldehyde in the absence of tetrahydrofolate. The enzyme was also inactivated by D-alanine caused by the transamination of the active site pyridoxal phosphate to pyridoxamine phosphate. This substrate specificity was also observed with the rabbit liver isoenzymes. We conclude that the reaction mechanism and the active site structure of E. coli serine hydroxymethyltransferase are very similar to the mechanism and structure of the rabbit liver isoenzymes.

Iron uptake by teeth and bones: a Mossbauer effect study

Iron uptake (Fe2+ and Fe3+) by bones, teeth, and dental enamel was studied, in vivo and in vitro, by chemical, powder X-ray diffraction and Mossbauer spectroscopy methods. Atomic absorption tests have revealed the permanent uptake of small amounts of iron by dental enamel soaked in vitro in solutions containing Fe2+. Mossbauer spectra show that the iron attached to the dental enamel stays at the same valency it had in the soaking solutions. Mossbauer measurements of in vivo samples show that iron is present in bones and teeth mainly as Fe3+ (10% Fe2+ in teeth), in compound similar to FeOOH. Iron is released or exchanged from teeth at a much lower rate than from bones.

Localization of the parallel elastic components in frog skinned muscle fibers studied by the dissociation of the A- and I-bands

Localization of the parallel elastic components (PECs) in skinned muscle fibers was investigated by analyzing the change of the resting tension, which accompanies the dissociation of the A- and I-bands. The A-band was dissociated from both ends by increasing the concentration of KCl under relaxing conditions (0.09-0.54 M KCl, 4.0 mM MgATP, 1.0 mM Mg2+, 4.0 mM EGTA, pH 6.0-9.0, 20 degrees C). At sarcomere lengths greater than or equal to 3.5 microns, the length of the A-band was estimated by comparing the intensity of the first-order optical diffraction line with the results of model calculations. These results were supported by differential-interference microscopy and sodium dodecyl sulfate gel electrophoresis. It was shown that the resting tension decreased nearly in proportion to the residual length of the A-band. At sarcomere lengths less than or equal to 4.0 microns, the resting tension after the dissociation of the A-band was lowered to less than 10% of the initial value. On the other hand, at sarcomere lengths greater than or equal to 5.0 microns the resting tension after the dissociation of the A-band still showed approximately 35% of the initial value and did not change even after the I-band was dissociated by a solution containing KI. From these results, we propose that most of the PECs contributing to resting tension bind almost uniformly to the A-band and there are also PECs connecting Z-lines.

[Inhibitors of reverse serotonin uptake and of specific imipramine binding in human blood plasma]

Human blood plasma contains low-molecular substances that inhibit in a dose-dependent manner both high-affinity specific binding of imipramine and reverse serotonin uptake by platelets. Incubation of human blood plasma with alumina was made use of to extract and study these imipramine-like inhibitors. The extract obtained from human blood plasma inhibited imipramine binding and reverse uptake of serotonin with median inhibitory concentrations of 0.18 +/- 0.1 and 0.36 +/- 0.15 mg/ml, respectively. After gel chromatography on Biogel P-2 the elution profile of the extract showed 2 major peaks of reverse serotonin uptake and imipramine binding inhibition and 3 additional peaks of reverse serotonin uptake inhibition, which did not have any considerable effect on imipramine specific binding. It is assumed that endogenous inhibitors of imipramine binding and reverse serotonin uptake are involved in the development of affective disorders.

Time-resolved x-ray diffraction studies of the sarcoplasmic reticulum membrane during active transport

X-ray and neutron diffraction studies of oriented multilayers of a highly purified fraction of isolated sarcoplasmic reticulum (SR) have previously provided the separate profile structures of the lipid bilayer and the Ca2+-ATPase molecule within the membrane profile to approximately 10-A resolution. These studies used biosynthetically deuterated SR phospholipids incorporated isomorphously into the isolated SR membranes via phospholipid transfer proteins. Time-resolved x-ray diffraction studies of these oriented SR membrane multilayers have detected significant changes in the membrane profile structure associated with phosphorylation of the Ca2+-ATPase within a single turnover of the Ca2+-transport cycle. These studies used the flash photolysis of caged ATP to effectively synchronize the ensemble of Ca2+-ATPase molecules in the multilayer, synchrotron x-radiation to provide 100-500-ms data collection times, and double-beam spectrophotometry to monitor the Ca2+-transport process directly in the oriented SR membrane multilayer.

Chemiluminescence in hypoxic brain--the second report: cerebral protective effect of mannitol, vitamin E and glucocorticoid

The effect of vitamin E, betamethasone and mannitol upon a series of pathological free radical reactions within hypoxic brain tissue was evaluated by the chemiluminescence method. Hypoxia was induced by arterial hypoxemia (PaO2 17-22 mmHg) with normocapnia (PaCO2 28-38 mmHg) and normotension (MABP 100-140 mmHg). 4% O2-96% N2 mixed gas was used to obtain the lowered PaO2. In the untreated group, increased chemiluminescence was measured in the hypoxic state and the early stage of the initial post-hypoxic state. In the groups administered vitamin E, betamethasone, mannitol and a combination of them reduced chemiluminescence was detected. To explore the reaction stage at which the drugs act in lipid peroxidation, chemiluminescence spectra was analyzed using the brain homogenate with the drugs added. Intensity peaks of the spectra were around at 480, 520-530, 570, 620-640, 680-700 nm before addition of the drugs. All the intensity peaks diminished after addition of vitamin E and betamethasone, but very little decrease occurred after mannitol. The lowered chemiluminescence value may indicate the free radical scavenging action of vitamin E, betamethasone and mannitol in vivo. Chemiluminescence spectrum analysis shows that vitamin E and betamethasone act on the late chain reaction following hydroperoxide and mannitol acts on the early reaction--generation of active oxygens.

Peroxidative oxidation of bilirubin during prostaglandin biosynthesis

The peroxidative oxidation of bilirubin has been characterized in the ram seminal vesicle microsomal system. The oxidation was monitored by following the loss in absorbance of bilirubin at 440 nm. Bilirubin behaves as a peroxidase substrate for prostaglandin H synthase. The oxidation may be initiated by the addition of arachidonic acid or peroxides to incubations containing ram seminal vesicle microsomes and bilirubin, and is sensitive to inhibition by reduced glutathione. The arachidonate-dependent oxidation, but not the peroxide-initiated case, is inhibited by indomethacin. Similar results were obtained using microsomal preparations from mouse, rat, and pig lungs. Spectral and chromatographic examination of the products of bilirubin oxidation in the ram seminal vesicle system demonstrate that biliverdin is produced in this system by the dehydrogenation of bilirubin, but that this product accounts for only about 15% of the bilirubin consumed. Biliverdin itself is not oxidized in this system. At least three highly polar, fluorescent products also are formed from bilirubin. Though not identified, these polar products differ markedly in chromatographic behavior from the major fluorescent products obtained following the singlet oxygen oxidation or the autoxidation of bilirubin.

Proton NMR spectroscopy of rabbit renal cortex

High resolution 1H-NMR spectra were obtained from renal cortical slices, homogenates, isolated cells in suspension, and lysates. Experimental conditions for acquisition of high resolution spin-echo spectra are described and assignments of prominent peaks to various metabolites are given. The in situ activity of the highly active cortical enzyme prolidase was determined (1.8 nmoles/min/mg wet kidney wt) by exploiting the marked difference in the spectral features of glycyl-L-proline and that of the free amino acids. The results suggest that this NMR method will be applicable generally to the study of hydrolysis of peptides, as well as to other metabolic processes both in vitro and in vivo.

Astronomical identification of the C3H radical

The C3H radical, a linear carbon chain with a 2 pi electronic ground state, has been identified in the millimeter-wave spectra of two astronomical sources, IRC +10216 and TMC-1, and conclusively confirmed (accompanying Letter) in a laboratory glow discharge. In IRC +10216 four rotational transitions have been observed, three in the lower fine-structure ladder (2 pi 1/2) and one in the upper (2 pi 3/2), each a resolved or partially resolved lambda-doublet. In TMC-1, both lambda components of the lowest lying 3/2 --> 1/2 transition of the 2 pi 1/2 ladder have been observed, each with well-resolved hfs. In IRC +10216 the excitation of C3H is similar to that of SiCC: the rotational temperature Trot within the 2 pi 1/2 ladder is low (8.5 K), owing to rapid radiative decay, while Trot across the ladders is high (approximately 52 K) because interconnecting far-IR radiative transitions are only weakly permitted. The column density of C3H in IRC +10216 averaged over the estimated source diameter of 84" is 2.8 x 10(13) cm-2, an order of magnitude less than that of C2H and C4H. A determination of the spectroscopic constraints of C3H that permitted the entire radio spectrum of this molecule to be calculated to high accuracy has been derived from analysis of the combined astronomical and laboratory data presented in the accompanying Letter.

Spectroscopic characteristics of human melanin in vivo

In this paper we present the absorption characteristics of human melanin in the visible range of wavelengths and specifically in the range 620-720 nm. The spectroscopy of melanin is studied by measuring remittance spectra of normal skin and vitiligo-involved skin of volunteers-patients. It is assumed that the spectral differences between adjacent areas of normally pigmented skin, and to some degree amelanotic skin, can only be due to the variations of the melanin filter. The ratio of the remittance spectrum of the vitiligo-involved skin with the spectrum of the normal skin in the range 620-720 nm can be fitted with a straight line for all the volunteers. A very strong correlation is obtained between the intercept and the slope for all the volunteers, which leads us to conclude that it is indeed melanin that we are measuring in all the volunteers and that it is the same substance spectroscopically for all the volunteers.

Characterization of rat cytochrome P-450MC synthesized in Saccharomyces cerevisiae

Rat cytochrome P-450MC cDNA was expressed in Saccharomyces cerevisiae AH22, SHY3 and NA87-11A cells under the control of the yeast ADH1 promoter and terminator. Although the three yeast strains transformed with the constructed expression plasmid, pAMC1, contained approximately three copies of the plasmid, the levels of both P-450MC mRNA and the corresponding protein in the AH22 cells carrying plasmid pAMC1 were 1.4- to 1.7-fold and 2-fold higher than in the other two strains, respectively. The P-450MC protein was purified from the microsomal fraction of AH22 cells carrying pAMC1 by a rapid purification method. The apparent molecular weight, chromatographic behavior, spectral properties, substrate specificity and immunochemical properties of the purified P-450MC protein were indistinguishable from those of rat liver P-450MC-I and P-450MC-II (Sasaki, T., et al. (1984) J. Biochem. 96, 117-126). The NH2-terminal amino acid sequence of the purified protein up to 10 residues was the same as those of P-450MC-I and P-450MC-II. In addition, HPLC analysis of the microsomal fraction of AH22 cells containing pAMC1 indicated that the synthesized P-450MC protein corresponds to P-450MC-II, but not P-450MC-I. With another purification method, we obtained the cleaved P-450MC protein which lacked the NH2-terminal 30 amino acids of intact P-450MC. The spectral properties and monooxygenase activities towards benzo(a)pyrene and 7-ethoxycoumarin of the cleaved P-450MC were nearly the same as those of intact P-450MC.

[Detection and quantification of carotid atheroma. Respective value of vascular ultrasonography, spectrum analysis and digital intravenous angiography]

This retrospective study involved 37 subjects who were examined by means of intravenous digitalised angiography, vascular ultrasonography and spectral analysis of the Doppler signal. The last two examinations were found to give the most precise images and functional information. The concordances between angiography and ultrasonography on the one hand and spectral analysis on the other were 82 and 90 per cent. The authors have established a protocol in order to limit and systematize these examinations during screening for carotid atheroma: the risk factors are weighted; a score is obtained by summation; depending on the value of this score and the patient's age, the investigation procedure is pursued or not. The sequence always consists of ultrasonography followed by spectral analysis when plaque is detected and by angiography when the plaque is stenotic or ulcerated. In symptomatic patients, ultrasonography and digitalised angiography are performed routinely.

A complex T-matrix derivation of a resonance amplitude

A resonant transition amplitude, valid to arbitrary order, is derived through the use of a complex energy T-matrix. A feature of this amplitude is its generality and simplicity making it useful for widespread applications in resonance theory.

Comparative studies on photoreactivation of ultraviolet light-induced T4 endonuclease susceptible sites and sister-chromatid exchanges in Potorous cells

Photoreactivation (PR) of T4 endonuclease-susceptible sites (ESS) and sister-chromatid exchanges induced by ultraviolet light was investigated in Potorous tridactylis Pt K2 cells, using monochromatic light from a grating monochromator. Both ESS and SCE showed maximum PR at 350 nm and the action spectra of PR essentially overlapped between ESS and SCE at 350, 400 and 450 nm. Exposure to 325-nm light after UV irradiation induced additional ESS and SCE, but reduction of ESS was shown by increasing exposure to 325-nm light, and further induction of SCE was observed by the same treatment. A possible difference in mechanisms between induction of ESS and SCE is suggested at 325 nm, while similar causes for ESS and SCE, presumably pyrimidine dimers, are suggested by UV (254-nm) irradiation.

Biologically active organotin polymers

The synthesis, structure, and properties of polymers in which tin is chemically anchored as tributyltin carboxylate are discussed. A base copolymer with anhydride or carboxyl groups is partially esterified with tributyltin oxide; the free carboxyls are then reacted with diepoxides to yield cross-linked controlled release formulations. The network structure and the separation length and type of epoxide cross-links were altered by changing the degree of esterification of the base polymer, the structure of epoxy monomer, and catalyst. NMR evidence established that rapid exchange exists in tributyltin carboxylates; as a consequence even their interfacial reaction with chloride is fast, producing tributyltin chloride. Biotoxicity data obtained by studying the inhibition of marine and soil bacteria reveal that the type and degree of cross-linking have a significant effect on the size of inhibition zones. Tests in the ocean confirm effective biological activity against marine fouling organisms. Structural correlations with dynamic mechanical and dielectric properties suggest a viable program to investigate the dependence of tributyltin release on polymer matrix properties.

Carnitine and glucuronic acid conjugates of pivalic acid

The [1-14C]pivaloyloxyethyl ester of methyldopa administered to man and cynomolgus monkeys resulted in the elimination in the urine of 14C-pivalic acid metabolites. Pivaloyl glucuronide and pivaloyl carnitine were identified as the major radioactive urinary metabolites in monkey urine and human urine, respectively. N.m.r. analysis indicated that pivaloyl carnitine had a cyclic structure. Although the role of carnitine is in the transport of fatty acids across mitochondrial membranes, it may also function in the conjugation of carboxylic acid xenobiotics in humans.

Phospholipid vesicle targeting using synthetic glycolipid and other determinants

The interactions of carbohydrate-modified phospholipid vesicles with various isolated cell types in vitro have been studied to establish a better basis for understanding the mechanisms for recognition and transport of such modified vesicles in vivo. The physical basis for the use of perturbed angular correlation spectroscopy for the measurement of phospholipid vesicle integrity, and the kinetics of uptake of modified phospholipid vesicles by mouse peritoneal macrophage are first reviewed. The effects of variation of the chemical structure of the determinant and other factors indicate that the rate of uptake of cationic vesicles by mouse peritoneal macrophage is directly related to the distance that an amine group can be extended beyond the vesicle surface, and not, for example, to the stereochemistry of the carbohydrate determinant. The uptake mechanism appears to involve generalized phagocytosis and not a receptor-mediated mechanism, or an opsonization process that is not stereospecific.

The conformation of single stranded oligonucleotides and of oligonucleotide-oligopeptide complexes from their rotation relaxation in the nanosecond time range

The conformation of single stranded oligonucleotides is analysed by measurements of their rotation time constants. The oligomers are aligned to some degree by short electric field pulses; after pulse termination the transition to a random orientation is followed by measurements of the linear dichroism. An efficient deconvolution procedure is developed for evaluation of the experimental data obtained in the ns-time range. The increase of rotation time constants observed for chain lengths in the range from 14 to 22 residues are interpreted according to a weakly bending rod model providing a persistence length and a Stokes' diameter. The Stokes' diameters obtained for ribo- and deoxyriboadenylates are about 13A, in approximate agreement with the expectation for a single stranded helix. The persistence length L = 53A corresponding to approximately 16 nucleotide residues found for riboadenylates at 2 degrees C appears to reflect relatively strong stacking interactions at this temperature. However, a comparison with the average length of stacked residues evaluated from available thermodynamic parameters of base stacking indicate that unstacked residues are not completely flexible. Apparently the ribose-phosphate chain provides an essential contribution to the stiffness of oligomers and polymers, even when the bases are unstacked. Addition of 100 microM Mg2+ leads to an increase of the persistence length to 88A. Corresponding measurements with deoxyriboadenylates show a slightly lower value of the persistence length than that found for riboadenylates. Addition of LysTrpLys and LysTyrLys to A(pA)19 leads to an increase of the rotation time constant, which corresponds approximately to a length increment by one residue per bound peptide. Since controls performed with LysLeuLys do not show any similar effect, the increase of the time constants induced by LysTrpLys and LysTyrLys is attributed to intercalation of the aromatic amino acids.

Relative roles of K region and bay region towards determining the carcinogenic potencies of polycyclic aromatic hydrocarbons

Using the quantum mechanical MINDO/3 method a bond reactivity index based on superdelocalization of electrons in a compound has been formulated in order to estimate the relative carcinogenic properties of polycyclic aromatic hydrocarbons. The values of the index calculated for the K region as well as the bay region suggest that a knowledge of the reactivities of both regions is necessary for a reasonable estimation of the relative carcinogenic potencies of PAHs. However, no direct relationship between the two reactivity indices was observed in the calculations. It was found that the results for the bay-region reactivity index correlated well with the relative carcinogenic potencies of the molecules.

Influence of incorporated bromodeoxyuridine on the induction of chromosomal alterations by ionizing radiation and long-wave UV in CHO cells

Incorporation of BrdUrd into nuclear DNA sensitizes CHO cells (1) to the induction of chromosomal aberrations by X-rays and 0.5 MeV neutrons and (2) to induction of chromosomal aberrations and SCEs by lw-UV. We have attempted to establish a correlation between induced chromosomal alterations and induced single- or double-strand breaks in DNA. The data show that while DSBs correlate very well with X-ray-induced aberrations, no clear correlation could be established between lw-UV induced SSBs (including alkali-labile sites) and chromosomal alterations. In addition the effect of 3-aminobenzamide (3AB) on the induction of chromosomal aberrations and SCEs induced by lw-UV has been determined. It is shown that 3AB is without any effect when lw-UV-irradiated cells are posttreated with this inhibitor. The significance of these results is discussed.