Lactogenesis in the rat. Changes in metabolic parameters at parturition

1. Tissue concentrations of nucleic acids, protein, fat, water, metabolites and lactose, and the activities of seven enzymes concerned in milk biosynthesis, were measured in the rat mammary gland at closely spaced times before, at and after parturition. 2. Changes are seen in the tissue concentrations of most substances, and several changes are initiated at least during the day preceding parturition. 3. Lactose, which is absent 1 day before parturition, is found in amounts of 12mumoles/g. fresh wt. of tissue at parturition. 4. From the tissue activities before parturition of three enzymes on the biosynthetic pathway of lactose, and, from the small changes observed in their activities at parturition itself, it is concluded that the factors responsible for the appearance of lactose at parturition remain to be demonstrated.

Molecular preservation in Late Cretaceous sauropod dinosaur eggshells

Exceptionally preserved sauropod eggshells discovered in Upper Cretaceous (Campanian) deposits in Patagonia, Argentina, contain skeletal remains and soft tissues of embryonic Titanosaurid dinosaurs. To preserve these labile embryonic remains, the rate of mineral precipitation must have superseded post-mortem degradative processes, resulting in virtually instantaneous mineralization of soft tissues. If so, mineralization may also have been rapid enough to retain fragments of original biomolecules in these specimens. To investigate preservation of biomolecular compounds in these well-preserved sauropod dinosaur eggshells, we applied multiple analytical techniques. Results demonstrate organic compounds and antigenic structures similar to those found in extant eggshells.

An antiviral mechanism of nitric oxide: inhibition of a viral protease

Although nitric oxide (NO) kills or inhibits the replication of a variety of intracellular pathogens, the antimicrobial mechanisms of NO are unknown. Here, we identify a viral protease as a target of NO. The life cycle of many viruses depends upon viral proteases that cleave viral polyproteins into individual polypeptides. NO inactivates the Coxsackievirus protease 3C, an enzyme necessary for the replication of Coxsackievirus. NO S-nitrosylates the cysteine residue in the active site of protease 3C, inhibiting protease activity and interrupting the viral life cycle. Substituting a serine residue for the active site cysteine renders protease 3C resistant to NO inhibition. Since cysteine proteases are critical for virulence or replication of many viruses, bacteria, and parasites, S-nitrosylation of pathogen cysteine proteases may be a general mechanism of antimicrobial host defenses.

Ca2+/calmodulin-binding peptides block phototransduction in Limulus ventral photoreceptors: evidence for direct inhibition of phospholipase C

Phototransduction in Limulus photoreceptors involves a G protein-mediated activation of phospholipase C (PLC) and subsequent steps involving InsP3-mediated release of intracellular Ca2+. While exploring the role of calmodulin in this cascade, we found that intracellular injection of Ca2+/calmodulin-binding peptides (CCBPs) strongly inhibited the light response. By chemically exciting the cascade at various stages, we found the primary target of this effect was not in late stages of the cascade but rather at the level of G protein and PLC. That PLCdelta1 contains a calmodulin-like structure raised the possibility that PLC might be directly affected by CCBPs. To test this possibility, in vitro experiments were conducted on purified PLC. The activity of this enzyme was strongly inhibited by CCBPs and also inhibited by calmodulin itself. Our results suggest that the calmodulin-like region of PLC has an important role in regulating this enzyme.

The effect of different molecular species of sphingomyelin on phospholipase C delta 1 activity

Bovine brain sphingomyelin was separated into different molecular species using a reverse phase column. PLC delta 1 was inhibited by all molecular species of sphingomyelin. The extent of this inhibition was dependent on the hydrophobicity. Based on fatty acid analysis, we conclude that the inhibition of PLC delta 1 depends on the chain length and degree of unsaturation of the fatty acid moiety of SM. N-palmitoyl-D-sphingomyelin and N-stearoyl-D-sphingomyelin inhibited PLC delta 1 less then N-oleoyl-D-sphingomyelin. In the absence of Ca2+ (1 mM EGTA) all tested molecular species of SM inhibited weakly the enzyme. The sensitivity of PLC delta 1 to inhibition by SM increased with increasing Ca2+ concentration. The shape of calcium curve differed for molecular species with saturated and unsaturated fatty acids. Inhibition of PLC delta 1 by N-palmitoyl-D-sphingomyelin and N-stearoyl-D-sphingomyelin reached a maximum at 0.2 microM Ca2+, while inhibition by N-oleoyl-D-sphingomyelin reached maximum at 2 microM Ca2+. PLC delta 1 is more sensitive to inhibition by SM when it is maximally activated by spermine and calcium and the extent of this inhibition depends on the length and degree of fatty acid unsaturation of the molecular species.

Isolation, cloning and characterization of a low-molecular-mass purine nucleoside- and nucleotide-binding protein

A purine nucleoside- and nucleotide-binding protein has been isolated from extracts of rat and rabbit heart, calf aortic smooth muscle and rat liver using an affinity column containing adenosine bound through the N6-position. The protein, which was eluted by adenosine, was cloned and expressed in Escherichia coli. The deduced amino acid sequence has a calculated Mr of 13693 (p13.7). The expressed protein has properties identical with the protein isolated from heart and liver, including an anomalous, apparent Mr of 15300, observed on gel electrophoresis. Gel filtration shows it to be a dimer. p13.7 differs by only three amino acids out of 125 from protein kinase C inhibitor 1 [Pearson, DeWald, Mathews, Mozier, Zürcher-Neely, Heinrikson, Morris, McCubbin, McDonald, Fraser et al. (1990) J. Biol. Chem. 265, 4583-4591]. However, we have not been able to demonstrate inhibition of protein kinase C by physiological concentrations of p13.7, regardless of whether it was isolated from tissue extracts or expressed in E. coli. p13.7 is a member of the histidine triad motif family of proteins [Séraphin (1992) J. DNA Sequencing Mapping 3, 177-179]. The affinity of p13.7 for a number of different purine nucleosides and nucleotides, as measured by fluorescence titration and gel filtration, falls within the range 5-50 microM. On the basis of these properties and its crystal structure [Brenner, Garrison, Gilmour, Peisach, Ringe, Petsko and Lowenstein (1997) Nature Struct. Biol. 4, 231-238], we have coined the acronym HINT (histidine triad nucleotide-binding motif) to describe the family of proteins of which p13.7 is a member. Other proteins that bind to the affinity column have been identified as malate and lactate dehydrogenases, cAMP-binding proteins, adenosine kinase and S-adenosylhomocysteine hydrolase.

Immunospecificity of albumin detected in 1.6 million-year-old fossils from Venta Micena in Orce, Granada, Spain

The Orce skull fragment from southern Spain, dated at 1.6 Myr, has been a subject of heated controversy since it was first discovered in 1982. If it is hominid, as its discoverers contend, it is by far the oldest fossil hominid yet found in western Europe and implies that human populations settled this region much earlier than was previously realized. Numerous stone artifacts found at the Orce sites provide evidence that hominids were indeed present there in the Lower Pleistocene. Some paleontologists maintain that the 8 cm diameter occipital fragment is from a horse, not a hominid. Two independent investigations of the residual proteins in the skull were undertaken, one at the University of Granada in Spain, the other at the University of California, San Francisco. Two immunological methods of comparable sensitivity were employed for detection and species attribution of protein extracted from fossil bone: the Granada team used an enzyme-linked-immunosorbent assay (ELISA), and the UCSF team used a radioimmunoassay (RIA). Both teams obtained reactions characteristic of human albumin in the Orce skull and horse albumin in some of the horse fossils. These results support the lithic evidence that hominids were living in Andalusia 1.6 million years ago.

Crystal structures of HINT demonstrate that histidine triad proteins are GalT-related nucleotide-binding proteins

Histidine triad nucleotide-binding protein (HINT), a dimeric purine nucleotide-binding protein from rabbit heart, is a member of the HIT (histidine triad) superfamily which includes HINT homologues and FHIT (HIT protein encoded at the chromosome 3 fragile site) homologues. Crystal structures of HINT-nucleotide complexes demonstrate that the most conserved residues in the superfamily mediate nucleotide binding and that the HIT motif forms part of the phosphate binding loop. Galactose-1-phosphate uridylyltransferase, whose deficiency causes galactosemia, contains tandem HINT domains with the same fold and mode of nucleotide binding as HINT despite having no overall sequence similarity. Features of FHIT, a diadenosine polyphosphate hydrolase and candidate tumour suppressor, are predicted from HINT-nucleotide structures.

Phospholipase C isoforms delta 1 and delta 3 from human fibroblasts. High-yield expression in Escherichia coli, simple purification, and properties

Phospholipase C isoforms delta 1 and delta 3 (PLC delta 1 and delta 3) were expressed in Escherichia coli using the cDNA sequences from human fibroblasts. The enzymes were also expressed with the sequence Met-Gly-His6-Ser-Gly-Leu-Phe-Lys-Arg, a hexahistidine sequence followed by a Kex2 protease cleavage site, denoted as "-H6K2," attached to their amino termini. PLC delta 1, PLC delta 1-H6K2, PLC delta 3, PLC delta 3-H6K2 all expressed in highly active form. The H6K2-bearing isoforms were each purified to homogeneity in a single step, with yields of 90-100%, using agarose-iminodiacetic acid-Ni columns and imidazole buffer as eluting agent. Yields in terms of activity increased as the temperature of expression was decreased. Expression at 16 degrees C for 72 h yielded 33 mg of pure PLC delta 1-H6K2 and 13 mg of pure PLC delta 3-H6K2 per liter of culture. Removal of H6K2 from both isoforms with Kex2 protease resulted in little or no loss of activity. Expression of PLC isoforms bearing -H6K2 at the amino terminus resulted in about 12 times more activity than expression of the isoforms lacking -H6K2. PLC delta 3 is much less stable than PLC delta1. Successful purification and storage of PLC delta 3 depends on a suitable stabilizing medium. Both isoforms require 0.3 microM calcium ion for half-maximum activity. The specific activities of the isoforms expressed with and without -H6K2 are the same, as are their calcium saturation curves.

A multifunctional vector system for heterologous expression of proteins in Escherichia coli. Expression of native and hexahistidyl fusion proteins, rapid purification of the fusion proteins, and removal of fusion peptide by Kex2 protease

Vectors have been constructed for the general purpose of expressing foreign proteins in E. coli. These vectors allow the production in high yield of either native proteins or of fusion proteins which contain, at their amino terminus, the peptide Met Gly His6 Ser Gly Leu Phe Lys Arg/, where Leu Phe Lys Arg/ is the recognition site for Kex2 protease which cleaves at the site indicated by /. The His6 sequence is used as a ligand for the one-step affinity purification of the expressed proteins on columns containing Ni or Zn ions chelated to iminodiacetic acid-agarose. After affinity chromatography, the purification peptide is cleaved off with Kex2 protease from Saccharomyces cerevisiae. The vectors also allow site-directed mutagenesis and sequencing of the cloned gene to be expressed without any intermediate subcloning. For practical examples of over-expression, affinity purification, and removal of the purification peptide, we chose a high-molecular-weight protein, phospholipase C gamma 1 (PLC gamma 1, M(r) 148,000) and a low-molecular-weight protein, Hit-1 (M(r) 16,000). Both were obtained pure and in high yield. PLC gamma 1 was fully active; the function of Hit-1 is not known. A set of companion vectors for co-expression of additional proteins has also been developed. These allow expression of proteins which enhance the production or activity of the protein of primary interest and of proteins which exhibit trans-interactions.

Gross cystic disease fluid protein in nipple aspirates of breast fluid of Asian and non-Asian women

Gross cystic disease fluid protein 15 (GCDFP-15) is universally present in the apocrine metaplastic epithelium of cystic breast disease and breast cancer, but it is rarely found in normal breast epithelium. Therefore GCDFP-15 detected in nipple aspirates of breast fluid (NAF) could serve as a biochemical marker of the presence and possibly extent of apocrine metaplasia within the breast. GCDFP-15 levels were measured in NAF from 37 Asian and 78 non-Asian women using radioimmunoassay. GCDFP-15 (range, 0-81,643 micrograms/ml) was found in the NAF of all but 1 woman and was highly correlated between right and left breasts. Mean concentrations of GCDFP-15 were significantly lower in NAF from Asian compared with non-Asian women. Markedly reduced levels of GCDFP-15 were found in the 17 women who had been parous in the previous 2 years. In women not parous within the prior 2 years, no relationship was found between GCDFP-15 levels and age, weight, age at menarche, first-degree family history of breast cancer, parity, oral contraceptive use, or smoking history. High concentrations of GCDFP-15 were found in the NAF of women with a history of a benign breast biopsy. Because similarly high levels of GCDFP-15 were found in NAF in over 40% of women without a history of benign breast biopsy, and because GCDFP-15 in the breast is produced only by apocrine metaplastic epithelium, we infer that the breasts of these women likely contain a significant degree of apocrine metaplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of phospholipase C delta 1 to phospholipid vesicles

Binding of phospholipase C delta 1 (PLC delta) to phospholipid vesicles was studied using large, unilamellar phospholipid vesicles (LUVs). PLC delta bound weakly to vesicles composed of phosphatidylserine (PS) or phosphatidylcholine (PC) or phosphatidylethanolamine (PE) + PC, and even more weakly to vesicles composed of phosphatidylinositol. The enzyme bound strongly to LUVs composed of PE + PC and phosphatidylinositol 4,5-bisphosphate (PIP2) or sphingomyelin (SM). Binding of 50% of PLC delta occurred at 0.25 nmol/ml PIP2 when LUVs composed of PE + PC (molar ratio of 80:20), plus various amounts of PIP2, were used at a constant phospholipid concentration of 300 nmol/ml. When LUVs composed of PE + PC + PIP2 (molar ratio of 79:20:1) were tested as a function of increasing phospholipid concentration, 50% binding of PLC delta occurred at 1.2 nmol/ml PIP2 and 120 nmol/ml total phospholipid. Similar measurements were conducted with other phospholipids and PIP2 at a molar ratio of 99:1. These showed that 50% binding of PLC delta occurred at a level of 0.9 nmol/ml PIP2 with 80 nmol/ml PC; at 2.2 nmol/ml PIP2 with 170 nmol/ml PS; at 4.2 nmol/ml PIP2 with 320 nmol/ml PI; and at 0.26 nmol/ml PIP2 with 20 nmol/ml total liver phospholipids. Binding to phosphatidylinositol 4-phosphate was much weaker. When LUVs composed of PE + PC + SM (molar ratio 48:12:40) were tested as a function of increasing phospholipid concentration, 50% binding of PLC delta occurred at a level of 96 nmol/ml SM. This is well below the concentration of SM that can be calculated to face the cytosol. Binding of PLC delta to LUVs decreased as the temperature was lowered from 37 degrees C to 0 degree C. Thus PLC delta shows a high degree of specificity for binding to PIP2 and SM. Under physiological conditions a considerable fraction of PLC delta may be bound to cellular membranes, either in an inactive form if bound to PIP2 at low resting Ca2+ concentrations, or in the inhibited form if bound to SM.

The role of inositol phospholipids in the association of band 4.1 with the human erythrocyte membrane

Band 4.1 is a major protein of the erythrocyte membrane skeleton. It promotes the binding of spectrin to F-actin and may anchor the skeletal network to the plasma membrane via its association with integral membrane proteins. Here, we have investigated the involvement of inositol phospholipids in the binding of band 4.1 to erythrocyte membranes using membrane vesicles stripped of all peripheral proteins at alkaline pH. Trypsinization of these vesicles allows the discrimination of two classes of band 4.1 binding sites: trypsin-sensitive sites (60-65% of the total), largely or exclusively on band 3, and trypsin-resistant sites (35-40% of the total), composed, at least in part, of the glycophorins. ATP depletion or activation of erythrocyte phosphoinositol phospholipase C led to a reduction in membrane phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] content by 20-70% in different experiments. The resulting decrease of band 4.1 binding to vesicles by was variable, but averaged about 15-20%. The same treatments led to an average decrease in the band 4.1 binding capacity of trypsinized vesicles of 55%. Since this is equivalent to a 20% decrease in the binding capacity of non-trypsinized vesicles (consistent with the above result), it indicates that PtdIns(4,5)P2 regulates the binding of band 4.1 only to trypsin-resistant binding sites (and to only a subset of these) accounting for about 15-20% of total band 4.1 binding sites on membranes. We found that hydrolysis of > 95% of PtdIns(4,5)P2 with exogenous phospholipase C-delta (PLC delta) resulted in no further decrease in band 4.1 binding to vesicles than did hydrolysis of 65-70% of PtdIns(4,5)P2 which is accessible to erythrocyte phosphoinositol phospholipase C. This suggests that only 65-70% of total membrane PtdIns(4,5)P2 is involved in regulating band 4.1 binding. Significantly, the pool of PtdIns(4,5)P2 involved is the same pool which can be hydrolysed by erythrocyte phosphoinositol phospholipase C, and which has been shown to be metabolically labile in erythrocytes. The membrane binding capacity for band 4.1 found in this study (averaging 1000 micrograms/mg vesicle protein) is considerably higher than that found in previous studies. The results are consistent with the existence of a binding site for band 4.1 on each copy of the major transmembrane proteins (band 3 and the glycophorins). These results provide new insights into the involvement of membrane inositol phospholipids in cytoskeletal-membrane interactions.

Inhibition of phospholipase C delta by hexadecylphosphorylcholine and lysophospholipids with antitumor activity

The antineoplastic compound hexadecylphosphorylcholine (HPC) was shown to be a highly effective inhibitor of phospholipase C delta (PLC delta 1), with an I50 of about 30 nmol/mL (30 microM) in the presence and absence of 200 microM spermine. A number of lysophospholipids, of which HPC can be considered to be a structural analog, also inhibited PLC. Lysosphingomyelin, lysophosphatidylserine, and lysophosphatidylcholine exhibited I50 values of 15, 10, and 7 nmol/mL, respectively, in the presence of 200 microM spermine. The I50 values were increased to 21-53 nmol/mL in the absence of spermine. N,N-Dimethylsphingosine and N,N,N-trimethylsphingosine, which inhibit the metastatic potential of human and murine tumor cells, were weak activators of PLC delta 1. It is postulated that HPC is more effective as an antineoplastic agent than lysophospholipids because HPC is metabolized slowly, while the lysophospholipids are metabolized rapidly in vivo.

Regulation of phospholipase C delta activity by sphingomyelin and sphingosine

Phospholipase C delta (PLC delta) is strongly inhibited by sphingomyelin (SM). The inhibition occurs in both the presence and the absence of spermine, an activator of PLC delta. Phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI) also inhibit PLC delta in the presence of spermine but are much less effective than SM. PE and PC activate and PS and PI inhibit PLC delta in the absence of spermine. Again, the inhibition by PS and PI is much weaker than the inhibition observed with SM. Similar or identical effects are observed in detergent micelle and liposome assays. Comparisons of physiological concentrations of SM with concentrations yielding 50% inhibition of PLC delta in vitro indicate that SM is likely to be a major factor in regulating the activity of PLC delta by inhibition. It is proposed that, in vivo, sphingomyelin acts as an inhibitor of PLC delta, which enables the enzyme to be regulated by activation. In certain circumstances, there is a substantial decline in SM and this may lead to a partial relief of the inhibition. PLC delta is activated by sphingosine in the absence of spermine. However, this activation occurs at unphysiologically high concentrations of sphingosine. The effects of SM and sphingosine on PLC delta in marked contrast to those observed with protein kinase C, which is unaffected by sphingomyelin and inhibited by sphingosine.

Scyphomedusae and their polyps are the same immunologically: implications for systematics

1. Polyp and medusa of the scyphozoans Aurelia aurita and Pelagia colorata (phylum Cnidaria) are indistinguishable by radioimmunoassay of whole animals, yet differ from other cnidarians against which they were tested. 2. We infer that proteins distinguishing species swamp those that differentiate the two (very distinct) life history phases. 3. Thus, at least for some taxa and some systematic techniques analyzing proteins, using organisms at the same developmental phase may be unnecessary, contrary to conventional wisdom.

An extended method for separating and quantitating molecular species of phospholipids

An improved and extended method for separating and quantitating molecular species of four phospholipid classes is presented. Crude lipid extract is first separated into phospholipid classes on a silica column. Each phospholipid class is then separated into molecular species without derivatization using high-performance liquid chromatography on columns packed with octadecyl silica. Quantitation of individual species is achieved by measuring absorbance at 205 nm. Factors for converting absorbancies to mol fractions have been determined. Quantitation by absorbance at 205 nm agrees well with quantitation by gas chromatography which is preferred to quantitation by phosphate analysis. One hundred phospholipid species have been identified. A table of relative retention times of molecular species is provided. Examples of quantitative analyses of species composition are presented.

Effect of omega 3 and omega 6 fatty acids on transformation of cultured cells by irradiation and transfection

Mouse embryo fibroblasts (C3H 10T1/2) were exposed to 4 Gy of gamma-rays. The cells yielded 5-8 transformed foci per 10(4) surviving cells. Addition of 100 microM of either eicosapentaenoate or docosahexaenoate to the tissue culture medium reduced the number of transformed foci to 0-1.4. C3H 10T1/2 and NIH 3T3 cells were transfected with plasmid T24 containing the Harvey ras oncogene. C3H 10T1/2 cells yielded 0.85-1.1 foci/ng DNA, while NIH 3T3 cells yielded 0.12-0.14 foci/ng DNA. Foci formation was suppressed 65% in C3H 10T1/2 cells and 93% in NIH 3T3 cells when 100 microM eicosapentaenoate was present in the culture medium. Docosahexaenoate had a similar but somewhat weaker effect. Addition of arachidonate to the medium had little or no effect. Cells grown in the presence of added eicosapentaenoate or docosahexaenoate produced much less prostaglandin E when challenged with calcium ionophore A23187. This is a reflection of changes in arachidonate production or utilization that occur during transformation which are suppressed by the added omega 3 fatty acids. Addition of eicosapentaenoate or docosahexaenoate to the culture medium resulted in extensive remodeling of the molecular species of the four major phospholipid classes that were examined. In its simplest form, omega 3-fatty acid-containing species substantially replaced omega 6-fatty acid-containing species. However, many more subtle changes occurred, and the different phospholipids responded differently to different polyunsaturated fatty acids. A feature of C3H 10T1/2 cells was their preferential accumulation of molecular species of 22-carbon fatty acids such as docosapentaenoate (22:5 omega 3) and docosatetraenoate (22:4 omega 6) in preference to eicosapentaenoate (20:5 omega 3) and eicosapentaenoate (arachidonate, 20:4 omega 6). It is proposed that the protective effect of eicosapentaenoate and docosahexaenoate arises out of the changes in the composition of the fatty acids that are released from one or more phospholipids by the action of phospholipases. The changes consist of a reduced release of arachidonate, the normal substrate of cyclooxygenase and lipoxygenases, and a greatly increased release of eicosapentaenoate and docosahexaenoate, which inhibit one or more of these enzymes, or form oxygenated products which are not as active as the arachidonate-derived products. Other mechanisms are also considered.

Inhibition of phosphorylation of troponin I in rat heart by adenosine and 5'-chloro-5'-deoxyadenosine

We have investigated the effects of adenosine on protein phosphorylation in extracts of rat heart. Incubation of a myofibrillar fraction with [gamma-32P]ATP resulted in the phosphorylation of several proteins by endogenous protein kinases. The adenosine analog 5'-chloro-5'-deoxyadenosine inhibited the phosphorylation of a 29 kD protein in this preparation. The protein was identified as cardiac troponin I (cTnI) by two-dimensional gel electrophoresis, using purified cTnI as standard. Addition of the catalytic subunit of cAMP-dependent protein kinase to the myofibrillar fraction increased phosphorylation of cTnI; this increase was inhibited by 5'-chloro-5'-deoxyadenosine and adenosine. Phosphorylation of purified cTnI by the catalytic subunit was also inhibited by 5'-chloro-5'-deoxyadenosine. Under these conditions used, 50% inhibition of phosphorylation by either endogenous or exogenous kinase was observed at approximately 50 microM 5'-chloro-5'-deoxyadenosine or adenosine. The inhibition described here occurred independently of catecholamines. The effects of ADP, AMP, and adenine on cTnI phosphorylation are also described.

Activation of phosphoinositide-specific phospholipase C delta from rat liver by polyamines and basic proteins

Phospholipase C from rat liver with a molecular weight of 87,000 (PLC delta) is stimulated by polyamines, basic proteins, and basic polyamino acids. The activation occurs in both the presence and the absence of detergents. Half-maximum activation by spermine is observed at 0.15 mM, with optimum effects between 0.2 and 0.5 mM. Spermine inhibits above 0.5 mM. Half-maximum activation by spermidine and putrescine is observed at 0.9 and 6 mM, respectively, with optimum effects at 2 and 5 mM, respectively. These polyamines also inhibit at higher concentrations. Neomycin activates the enzyme with an optimum concentration of 10 microM, but maximum activation is less than with polyamines. Half-maximum activation by histone 2B occurs at 0.5 micrograms/ml (36 nM), with maximum stimulation at 1.5 micrograms/ml. Other histones, protamine, melittin, poly-L-ornithine, poly-L-lysine, poly-D-lysine, and poly-L-arginine, activate optimally at 3-10 micrograms/ml. Myelin basic protein and lysozyme activate optimally at 50-100 micrograms/ml. Typical activations are three- to eightfold, but under some conditions the enzyme shows little or no activity in the absence of basic activators. The basic activators lower the salt concentration required for maximal activity. In the case of the detergent-micelle assay, histone shifts the optimum NaCl concentration from 350 to 200 mM for PIP2, from 260 to 100 mM for PIP, and from 150 to 0 mM for PI. Histone potentiates the activation by Ca2+, but does not shift the optimum Ca2+ concentration. The optimum salt and Ca2+ concentrations are linked, such that a decrease in the concentration of one decreases the optimum concentration of the other. Activation by histone is diminished by MgCl2 in a concentration-dependent manner.

5'-Nucleotidase I from rabbit heart

5'-Nucleotidase I (N-I) from rabbit heart was purified to homogeneity. After ammonium sulfate precipitation, the purification involved chromatography on phosphocellulose, DEAE-Sepharose, AMP-agarose, and ADP-agarose. The pure enzyme has a specific activity of 318 mumol (mg of protein)-1 min-1. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate yields a subunit molecular weight of 40,000. N-I is activated by ADP but not by ATP, in contrast to the 5'-nucleotidase (N-II) purified by Itoh et al. (1986), which is activated by ATP and, less well, by ADP. N-I displays sigmoidal saturation kinetics in the absence of ADP and hyperbolic kinetics in the presence of ADP. Partially purified N-I was previously shown to prefer AMP over IMP as substrate (Truong et al., 1988); this has been confirmed for pure N-I. Comparison of AMP and ADP concentrations reported to occur in heart with the kinetic behavior of N-I implicates N-I as the enzyme responsible for producing adenosine under conditions leading to a rise in ADP and AMP, such as hypoxia or increased workload. N-I is not activated by the ADP analogue adenosine 5'-methylenediphosphonate (AOPCP) and is only weakly inhibited by relatively high concentrations of AOPCP, in contrast to 5'-nucleotidase from plasma membrane, which is powerfully inhibited by this analogue. N-I shows an absolute dependence on Mg2+ ions. Mn2+ and Co2+ ions can replace Mg2+ ions as activator; Ni2+ and Fe2+ are much less effective, while Ca2+, Ba2+, Zn2+, and Cu2+ fail to activate the enzyme.

The involvement of carnitine intermediates in peroxisomal fatty acid oxidation: a study with 2-bromofatty acids

Metabolism-dependent inactivators of 3-ketothiolase I and carnitine acyltransferase I (CAT I) have been used to study the oxidation of fatty acids in intact hepatocytes. 2-Bromooctanoate inactivates mitochondrial and peroxisomal 3-ketothiolases I in a time-dependent manner. During the first 5 min of incubation, inactivation of 3-ketothiolase in mitochondria is five times faster than its inactivation in peroxisomes. Almost complete inactivation of 3-ketothiolase I in both types of organelle is achieved after incubation with 1 mM 2-bromooctanoate for 40 min. The inactivation is not affected by preincubating hepatocytes with 20 microM tetradecylglycidate (TDGA), an inactivator of CAT I, under conditions which cause greater than 95% inactivation of CAT I. 2-Bromododecanoate (1 mM) causes 60% inactivation of mitochondrial and peroxisomal 3-ketothiolases I in 40 min. These inactivations are greatly reduced by preincubating hepatocytes with 20 microM TDGA, demonstrating that 2-bromododecanoate enters both mitochondria and peroxisomes via its carnitine ester. 2-Bromopalmitate (1 mM) causes less than 5% inactivation of mitochondrial and peroxisomal 3-ketothiolases I in 40 min, but causes 95% inactivation of CAT I during this time. Incubation of hepatocytes with 10-200 microM 2-bromopalmitoyl-L-carnitine causes inactivation of mitochondrial and peroxisomal 3-ketothiolases I at similar rates. This inactivation is decreased by palmitoyl-D-carnitine during the first 5 min of incubation. Pretreating hepatocytes with 20 microM TDGA does not affect the inactivation of mitochondrial or peroxisomal 3-ketothiolase I by 2-bromopalmitoyl-L-carnitine. These results demonstrate that in intact hepatocytes, peroxisomes oxidize fatty acids of medium-chain length by a carnitine-independent mechanism, whereas they oxidize long-chain fatty acids by a carnitine-dependent mechanism.

Selective inactivation of peroxisomal and cytosolic 3-ketothiolase IB by 2-chloro-6-phenylhexanoate in intact hepatocytes

Rat liver mitochondria and cytosol contain two types of 3-ketothiolases, namely 3-ketothiolases IA and IB, which cleave 3-ketoacyl-coenzyme A (CoA) esters containing four or more carbons and 3-ketothiolases IIA and IIB, which cleave 3-ketoacyl-CoA esters containing four carbons, i.e. acetoacetyl-CoA (Aragon, J.J., and Lowenstein, J.M. (1983) J. Biol. Chem. 258, 4725-4733). We now report that rat liver peroxisomes also contain 3-ketothiolases IA and IB and show that incubation of hepatocytes with 2-chloro-6-phenylhexanoate causes the selective inactivation of peroxisomal and cytosolic 3-ketothiolase IB, while mitochondrial 3-ketothiolases are not appreciably affected. The basis of the selectivity of the inhibitor for peroxisomal and cytosolic 3-ketothiolases can be accounted for in terms of the specificities of the enzymes in the different pathways of beta-oxidation. Evidence is presented that 2-chloro-6-phenylhexanoate is metabolized to 2-chloro-3-keto-6-phenylhexanoyl-CoA, which then alkylates 3-ketothiolase and thereby inactivates the enzyme. Evidence is presented which suggests that cytosolic 3-ketothiolases IA and IB are not artifacts of homogenization and organelle preparation.

The purine nucleotide cycle revisited [corrected]

This review is restricted to the operation of the purine cycle in mammalian muscle. A previous review provided a summary of early evidence for the operation of the cycle and of various functions proposed for the cycle. It also provided a brief history of work on ammonia production by muscle and other tissues and of the discovery of the enzymes of the purine nucleotide cycle. Recent reviews on the purine nucleotide cycle include those of Terjung et al. and van Waarde.

Polyphosphoinositides produced by phosphatidylinositol 3-kinase are poor substrates for phospholipases C from rat liver and bovine brain

The ability of three pure types of bovine brain phospholipase C (PLC) and one pure rat liver PLC to utilize as substrates the recently discovered phosphatidylinositol 3-phosphate (PI-3-P), a putative phosphatidylinositol 3,4-bisphosphate (PI-3,4-P2), and phosphatidylinositol trisphosphate (PIP3) was investigated. PI-3-P, PI-3,4-P2, and PIP3 are the products of phosphorylation of PI, PI-4-P, and PI-4,5-P2, respectively, by phosphoinositide 3-kinase activities that are associated with certain protein-tyrosine kinases. Although these new phospholipids have been found in intact cells, PI-3,4-P2 and PIP3 appear only after stimulation of quiescent cells with growth factors such as platelet-derived growth factor (Auger, K. R., Serunian, L. A., Soltoff, S. P., Libby, P., and Cantley, L. C. (1989) Cell 57, 167-175) and after transformation by certain oncoproteins (L. A. Serunian, K. R. Auger, T. M. Roberts, and L. C. Cantley, manuscript in preparation). Mixtures of [3H]PI-4-P plus [32P]PI-3-P or [3H]PI-4,5-P2 plus [32P]PI-3,4-P2 or PIP3 alone were used as substrates for PLCs in vitro. After incubation with enzyme followed by extraction with chloroform/methanol/HCl, the ratio of 3H/32P in the aqueous layer revealed the selective hydrolysis of PI-4-P and PI-4,5-P2 over PI-3-P and PI-3,4-P2. High performance liquid chromatography analysis of the aqueous layer containing reaction products confirmed that only PI-4-P and PI-4,5-P2, were hydrolyzed to inositol 1,4-P2 and inositol 1,4,5-P3, respectively. These findings suggest that the turnover of PI-3-P, PI-3,4-P2, and PIP3 occurs independently of the turnover of PI-4-P and PI-4,5-P2.

28 kDa adenosine-binding proteins of brain and other tissues

Membranes prepared from calf brain were solubilized and chromatographed on a column containing 5'-amino-5'-deoxyadenosine covalently linked to agarose through the 5'-amino group. When the column was eluted with adenosine, a pure protein emerged with subunit molecular mass of 28 kDa. The protein was extracted from the membranes with sodium cholate, but not with 100 microM-adenosine or 0.5 M-NaCl. A similar 28 kDa protein was isolated from the soluble fraction of calf brain. The yield of membrane-bound and soluble 28 kDa protein per gram of tissue was about the same. The 28 kDa protein was also found in membrane and soluble fractions of rabbit heart, rat liver and vascular smooth muscle from calf aorta. The yield per gram of tissue fell into the order brain greater than heart approximately vascular smooth muscle greater than liver for the 28 kDa protein from the membrane fraction, and brain approximately heart greater than vascular smooth muscle greater than liver for the 28 kDa protein from the soluble fraction. Polyclonal antibodies to pure 28 kDa protein from calf brain membranes cross-reacted with the 28 kDa protein from calf brain soluble fraction and with 28 kDa proteins isolated from other tissues. The 28 kDa protein from calf brain membranes was also eluted from the affinity column by AMP and 2',5'-dideoxyadenosine, but at a concentration higher than that at which adenosine eluted the protein, but N6-(R-phenylisopropyl)adenosine, 5'-N-ethylcarboxamidoadenosine, ADP, ATP, GTP, NAD+, cyclic AMP and inosine failed to elute the protein at concentrations up to 1 mM. The 28 kDa protein from the soluble fraction was not eluted by 3 mM-AMP or 1 mM-N6-(R-phenylisopropyl)adenosine,-5'-N-ethylcarboxamidoadenosine or -cyclic AMP. Unexpectedly, the soluble 28 kDa protein was eluted by AMP in the presence of sodium cholate. Soluble 28 kDa protein from calf brain had a KD for adenosine of 12 microM. Membrane 28 kDa protein from calf brain had a KD of 14 microM in the presence of 0.1% sodium cholate. Amino acid compositions of the 28 kDa proteins were similar, but not identical.

Regulation of soluble 5'-nucleotidase I from rabbit heart

Rabbit heart contains two soluble 5'-nucleotidases, termed N-I and N-II, which can be separated using phosphocellulose chromatography. N-I prefers AMP over IMP as substrate, in contrast to N-II which prefers IMP over AMP. Both enzymes require Mg2+, but the optimum Mg2+ concentrations for the two enzymes are different. High concentrations of NaCl inhibit N-I and activate N-II. Purified N-I is activated by ADP but not by ATP. According to Itoh et al. (1986), purified N-II is activated by both ADP and ATP. N-I has been purified approximately 1000-fold to a specific activity of approximately 100 mumol/mg protein/min. The properties of N-I suggest that it is the enzyme responsible for the release of adenosine from AMP under conditions of hypoxia or increased work load.

Purification of a phospholipase C from rat liver cytosol that acts on phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-phosphate

A soluble phospholipase C from rat liver was purified to homogeneity using phosphatidylinositol 4,5-bisphosphate (PIP2) as substrate. After ammonium sulfate fractionation, the purification involved chromatography on phosphocellulose, DEAE-Sepharose CL-6B, hydroxylapatite, Reactive Blue 2 dye-linked agarose, and Mono S cation exchanger. Under the conditions of the assay, the pure enzyme had a specific activity of 407 mumol/mg protein/min. It migrated as a single band with a molecular mass of 87 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The water-soluble product formed during the hydrolysis of PIP2 by the purified enzyme was inositol 1,4,5-trisphosphate. The enzyme shows one-half of maximum velocity at 2 microM Ca2+ with PIP2 as substrate. Between 0 and 100 microM Ca2+, the enzyme shows approximately the same activity with phosphatidylinositol 4-phosphate (PIP) as it does with PIP2, and very low activity with phosphatidylinositol. The enzyme is activated by low concentrations of basic proteins; for example, with PIP2 as substrate, 1 microgram/ml histone activates the enzyme 3.6-fold. The enzyme shows an almost absolute requirement for monovalent salts which can be met by different alkali metal halides. A second, minor peak of PIP2-hydrolyzing phospholipase C activity was resolved during chromatography of the enzyme on hydroxylapatite. The substrate specificity suggests that PIP and PIP2 are normal substrates of this enzyme. Under physiological conditions of activation, the enzyme may therefore generate inositol 1,4-bisphosphate and inositol 1,4,5-trisphosphate in amounts determined by the ratio of PIP and PIP2 present in the cellular membranes.

5'-Nucleotidases in rat heart. Evidence for the occurrence of two soluble enzymes with different substrate specificities

Chromatography of soluble proteins from rat heart on phosphocellulose columns separates two 5'-nucleotidases. The first to emerge from the column shows a preference for AMP over IMP as substrate, whereas the second shows a preference for IMP over AMP. The properties of the IMP-preferring enzyme, including the conditions under which it is eluted from phosphocellulose columns, show it to be the enzyme studied by Itoh, Oka & Ozasa [Biochem. J. (1986) 235, 847-851]. The kinetic properties of the AMP-preferring enzyme indicate that it is likely to be the enzyme responsible for the production of adenosine under conditions of hypoxia and increased work load, and with metabolic stresses such as a high load of acetate.

Changes in adenosine receptors during differentiation of 3T3-F442A cells to adipocytes

Incubation of undifferentiated 3T3-F442A cells (preadipocytes) with 5'-N-ethylcarboxamidoadenosine (NECA) increases intracellular cyclic AMP in a dose-dependent manner. The effect of NECA is antagonized by 8-phenyltheophylline, but potentiated by 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidine, an inhibitor of cyclic AMP phosphodiesterase. Incubation of preadipocytes with (-)-N6-(R-phenylisopropyl)adenosine (PIA) has no inhibitory effect on the basal concentration of cyclic AMP or on the stimulation of adenylate cyclase by isoprenaline or forskolin. Micromolar concentrations of PIA increase intracellular cyclic AMP, but with a lower potency than NECA. Similar findings are obtained with the non-differentiating cell line 3T3-C2. Thus preadipocyte 3T3-F442A cells and 3T3-C2 cells appear to express only stimulatory adenosine receptors. For some time after 3T3-F442A cells have differentiated to adipocytes, micromolar concentrations of NECA and PIA continue to increase cyclic AMP to a similar extent to that in preadipocytes, whereas nanomolar concentrations of PIA decrease the stimulatory effects of isoprenaline and forskolin on adenylate cyclase by 50%. However, several days after differentiation, the adipocytes gradually lose the major part of their positive response to NECA and reach a steady response to NECA 10 days after differentiation. The inhibition of adenylate cyclase caused by PIA remains constant for at least 2 weeks after differentiation. With membranes derived from the cells, the effects of NECA and PIA depend on GTP. These results indicate that, during the differentiation of 3T3-F442A cells to adipocytes, new inhibitory adenosine receptors are expressed, whereas the stimulatory receptors become attenuated.

Purification of adenylosuccinate lyase from rat skeletal muscle by a novel affinity column. Stabilization of the enzyme, and effects of anions and fluoro analogues of the substrate

Adenylosuccinate lyase from rat skeletal muscle was purified to apparent homogeneity by a combination of ion-exchange chromatography and affinity chromatography on agarose containing covalently bound adenylophosphonopropionate. The purified enzyme is stable when stored in 20% glycerol at -70 degrees C, and can be thawed and re-frozen with minimal loss of activity. Adenylosuccinate lyase has a specific activity of 11 mumol/min per mg of protein at 25 degrees C. Its subunit Mr is 52,000, by SDS/polyacrylamide-gel electrophoresis, and its apparent native Mr is approx. 200,000, by gel filtration. The purified enzyme has Km values for adenylosuccinate and 4-(N-succino)-5-aminoimidazole-4-carboxamide ribonucleotide (SAICAR) of 1.5 microM and approximately 1 microM respectively, in Hepes/KOH buffer, pH 7.4. Several monoanions and dianions activate the enzyme at low concentration; several of these inhibit the enzyme at high concentrations. Fluoro analogues of adenylosuccinate and SAICAR were synthesized by using highly purified adenylosuccinate synthase and SAICAR synthase respectively, and erythro-beta-fluoroaspartate in place of aspartate. Both analogues are competitive inhibitors of adenylosuccinate lyase in both of the reactions catalysed by the enzyme, with Ki values well below the Km values for the two substrates.

Inhibition of phosphatidylinositol kinase in vascular smooth muscle membranes by adenosine and related compounds

Adenosine and 5'-chloro-5'-deoxyadenosine inhibited the phosphorylation of phosphatidylinositol in membranes prepared from aortic smooth muscle. The nucleosides did not affect the breakdown of phosphatidylinositol-4-phosphate. Under certain conditions, the membrane-bound phosphatidylinositol kinase phosphorylated exogenous phosphatidylinositol. The nucleosides inhibited the enzyme competitively with respect to magnesium-ATP and non-competitively with respect to phosphatidylinositol. Adenosine analogs modified in the ribose moiety were inhibitors with potencies comparable to that of adenosine, whereas adenine nucleotides and purine-modified adenosine analogs were much weaker inhibitors. Density gradient fractionation studies showed that phosphatidylinositol kinase is primarily associated with the sarcoplasmic reticulum. Vascular smooth muscle contraction is associated with increased phosphatidylinositol turnover. Inhibition of phosphatidylinositol kinase by intracellular adenosine may, therefore, be a factor involved in regulating vasodilation.

Inhibition of adenylosuccinate lyase by L-alanosyl-5-aminoimidazole-4-carboxylic acid ribonucleotide (alanosyl-AICOR)

L-Alanosyl-5-aminoimidazole-4-carboxylic acid ribonucleotide (alanosyl-AICOR) has been synthesized enzymatically using 4-(N-succino)-5-aminoimidazole-4-carboxamide ribonucleotide (SAICAR) synthetase in conjunction with 5-aminoimidazole-4-carboxylic acid ribonucleotide and L-2-amino-3-(N-hydroxy-N-nitrosoamino)propionic acid (alanosine). The product was characterized by chromatography, ultraviolet spectrum and NMR spectrum at 300 MHz. Alanosyl-AICOR was not a substrate of adenylosuccinate lyase from rat skeletal muscle, but it was an apparent competitive inhibitor in both of the reactions catalyzed by the enzyme. The KI values for alanosyl-AICOR were approximately 1.5 and 1.3 microM in the SAICAR and adenylosuccinate cleavage reactions respectively. These KI values were essentially the same as the Km values for the two substrates of adenylosuccinate lyase. They compare with an accumulation of 70 microM alanosyl-AICOR in leukemic nodules of mice treated with alanosine [A. K. Tyagi and D. Cooney, Cancer Res. 40, 4390 (1980)]. Thus, inhibition of adenylosuccinate lyase may account for much of the inhibitory effect exerted by alanosyl-AICOR in vivo. We confirmed the previous observation that alanosyl-AICOR is an inhibitor of adenylosuccinate synthetase.

Effects of adenosine and adenosine analogues on glycogen metabolism in isolated rat hepatocytes

Adenosine and adenosine analogues were incubated with isolated rat hepatocytes. Adenosine and 5'-deoxy-5'-chloroadenosine stimulated glucose release, glycogen loss, and the conversion of glycogen phosphorylase b to a. The effect was of short duration for adenosine, but of long duration for 5'-deoxy-5'-chloroadenosine. The effects on glucose release and phosphorylase were blocked by theophylline, an R-receptor blocking agent, but not by nitrobenzylthioinosine or dipyridamol which are nucleoside transport inhibitors. A dose-dependent rise in cyclic AMP concentration was observed in hepatocytes 1 min after adding adenosine. It is concluded that adenosine exerts these effects in liver by activating adenylcyclase. Adenosine may be involved in the short-term regulation of hepatic glycogen phosphorylase.

Metabolism of threo-beta-fluoroaspartate by H4 cells. Inhibition of adenylosuccinate lyase by fluoro analogs of its substrates

DL-threo-beta-Fluoroaspartate is a substrate for the two enzymes in de novo purine biosynthesis that use aspartate, namely 4-(N-succino)-5-aminoimidazole-4-carboxamide ribonucleotide (SAICAR) synthetase and adenylosuccinate synthetase. With both enzymes, Vmax with threo-beta-fluoroaspartate is about 50% of that observed with aspartate. The products of the two enzyme reactions, threo-beta-fluoro-SAICAR and threo-beta-fluoroadenylosuccinate, are inhibitors of adenylosuccinate lyase purified from rat skeletal muscle. In 20 mM phosphate buffer, pH 7.4, the KI values for threo-beta-fluoro-SAICAR are 5 and 3 microM and for threo-beta-fluoroadenylosuccinate are 3 and 1 microM, in the SAICAR and adenylosuccinate cleavage reactions, respectively. In 20 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer, pH 7.4, the KI values for threo-beta-fluoro-SAICAR are approximately 0.14 and 0.03 microM and for threo-beta-fluoroadenylosuccinate are approximately 0.05 and 0.015 microM, in the same two reactions, respectively. These KI values are one-half to one-hundredth of the Km values for SAICAR and adenylosuccinate, the two substrates of adenylosuccinate lyase. After an 8-h incubation with 45 microM threo-beta-fluoroaspartate, H4 cells contain 200-300 microM threo-beta-fluoro-SAICAR and 60-90 microM threo-beta-fluoroadenylosuccinate. These concentrations of fluoro analogs are sufficient to substantially inhibit adenylosuccinate lyase and hence the de novo synthesis of purines in H4 cells.

A molecular link between the bats of New Zealand and South America

Along with the kiwis (Apteryx), tuatara (Sphenodon) and leiopelmatid frogs, the now rare lesser short-tailed bat (Mystacina tuberculata), one of only two species in the endemic family Mystacinidae, has long been viewed as one of New Zealand's archaic, mystery vertebrates, and has presented taxonomists with a major puzzle since its first description in 1843 (ref. 3). We report here the results of immunological comparisons involving the albumin and transferrin of Mystacina which indicate that its closest phylogenetic affinities are with the New World phyllostomoids--noctilionids, mormoopids and phyllostomoids. We estimate the separation between the Noctilio and Mystacina lineages to have occurred about 35 Myr ago.

Non-enzymic phosphorylation of polyphosphoinositides and phosphatidic acid is catalysed by bivalent metal ions

Phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-bisphosphate and phosphatidic acid undergo non-enzymic phosphorylation by ATP in the presence of bivalent metal ions. The non-enzymic reaction is more rapid in a mixture of water, chloroform and methanol than in water alone. Chemical evidence indicates that the product formed from phosphatidylinositol 4-phosphate is the corresponding 4-pyrophosphate. This product shows an RF value very close to that of phosphatidylinositol 4,5-bisphosphate on t.l.c. with an acidic solvent commonly used to characterize and measure the latter; however, it can be separated readily with an alkaline solvent. Chemical evidence indicates that the products formed from phosphatidylinositol 4,5-bisphosphate and phosphatidic acid are also pyrophosphates.

Immunological systematics of the extinct quagga (Equidae)

It has been debated whether the extinct quagga was a distinct fourth species of African zebra or whether it was merely the southern variant of the Plains zebra (Equus burchelli). Using a radioimmunoassay (RIA) technique, we have shown that proteins remaining in quagga skins from museums are much more similar to serum proteins of the Plains zebra than to those of the other two extant zebras.

Adenosine and 5'-chloro-5'-deoxyadenosine inhibit the phosphorylation of phosphatidylinositol and myosin light chain in calf aorta smooth muscle

Smooth muscle from calf aorta is homogenized and centrifuged. The insoluble material is subjected to sucrose density gradient centrifugation. When the heaviest fraction so obtained is incubated with radioactive ATP, two components incorporate most of the acid-insoluble radioactivity. One is a phosphoprotein with a molecular weight of 21,000. It has been identified as myosin light chain by its molecular weight, isoelectric point, and precipitation by antibody to calf aorta myosin. Its phosphorylation is strongly inhibited by EGTA, in agreement with published reports that myosin light chain kinase of smooth muscle is Ca2+ dependent. The other product is of low molecular weight, is extracted into acidic chloroform-methanol, and has been identified as phosphatidylinositol 4-phosphate. Adenosine and 5'-chloro-5'-deoxyadenosine, which are vasodilators, inhibit the phosphorylation of both substrates. Phosphorylation of phosphatidylinositol is inhibited at lower concentrations of the nucleosides than is the phosphorylation of myosin light chain. The inhibitory effects of the two nucleosides are not associated with changes in the concentration of cyclic AMP. The precise function of phosphatidylinositol phosphorylation in smooth muscle is not known, but correlations between smooth muscle contraction and increased turnover of phosphatidylinositol and its mono- and diphosphates have been reported. Myosin light chain is phosphorylated under conditions which favor smooth muscle contraction. We conclude that the inhibitory effects of adenosine described here are consistent with their physiological action as vasodilators.

A survey of enzymes which generate or use acetoacetyl thioesters in rat liver

Reactions that generate and remove acetoacetyl-CoA and acetoacetate were measured in mitochondria and cytosol of rat liver. The activities surveyed include acetoacetyl-CoA hydrolase, acetoacetyl-glutathione hydrolase, acetoacetyl-CoA:glutathione acyl transferase, 3-ketothiolases I and II, 3-hydroxy-3-methylglutaryl-CoA lyase and synthase, and acetoacetyl-CoA synthetase. Phosphocellulose chromatography shows that cytosol contains at least four acetoacetyl-CoA hydrolase activities, two of which do not coincide with 3-ketothiolases or 3-hydroxy-3-methylglutaryl-CoA lyase, while mitochondria contain at least three acetoacetyl-CoA hydrolase activities that overlap partially or completely with 3-ketothiolases and 3-hydroxy-3-methyl-glutaryl-CoA lyase. Two of the mitochondrial acetoacetyl-CoA hydrolase activities are not found in cytosol. Cytosol contains at least two and mitochondrial extracts at least six acetoacetyl-glutathione hydrolase activities. Mitochondria and cytosol both contain two isozymes of 3-ketoacyl-CoA thiolase (thiolases Ia and Ib). Chain length specificities show that the mitochondrial and cytosolic forms of thiolase Ia differ from each other. We report a new isozyme of 3-ketoacyl-CoA thiolase (thiolase I) in rat liver cytosol.