Acetylaspartate as an extramitochondrial physiological carrier of acetyl coA for fatty acid synthesis

Aminooxyacetate, a transaminase inhibitor, suppresses the enrichment in radioactivity found in the fatty acids of animals receiving 2, 4-¹⁴C citrate in comparison with 1, 5-¹⁴C citrate. On the other hand 3H from N-acetyl-³H aspartate is significantly incorporated into fatty acids $\text{in vivo}$ or in presence of liver supernatant fractions. Our results indicate that citrate seems to be an effective carrier of acetyl CoA for fatty acid synthesis mainly in the rat liver and that acetylaspartate may be an other physiological carrier of acetyl CoA outside the mitochondria.     

Controls of citrate synthase activity

The inhibition of citrate synthase by a variety of nucleotides and polycarboxylate compounds is not unexpected since many of the compounds are substrate analogs of citrate synthase. These effectors are interesting by virtue of the fact that many of them are intermediates and/or end products in the metabolic path of which citrate synthase can be considered the first committed step. As a consequence, it is possible to propose regulation of citrate synthase by ATP (or phosphorylation potential) by acyl CoA (acylation level) and NADH (redox potential). Aside from these putative controls, it is possible that the major control of citrate synthase activity is by changes in the concentration of its substrates acetyl CoA and oxalacetate.I discuss in this review the many factors that must be considered before one can decide whether or not interactions between metabolites and enzymes observed in an $\text{in vitro}$ catalytic situation have metabolic relevance. These factors include 1) the concentrations of substrates at the enzyme site, 2) the concentrations of effectors at the enzyme site, 3) the presence of modifying substances, and 4) the difference in behavior of an enzyme at its concentration $\text{in vivo}$ compared to its concentration $\text{in vitro}$. In the case of citrate synthase as is generally true for other enzymes, no accurate knowledge of these factors are available $\text{in vitro}$ so that little can be said concerning the $\text{in situ}$ control of citrate synthase, which may be the result of all the factors acting in concert. The studies of effectors on enzymes $\text{in vitro}$ can only serve as a guideline for parameters to study when techniques are available to study control of enzymes $\text{in situ}$.     

Regulation of rat liver microsomal glutathione S-transferase activity by thiol/disulfide exchange

The regulation of purified glutathione S-transferase from rat liver microsomes was studied by examining the effects of various sulfhydryl reagents on enzyme activity with 1-chloro-2,4-dinitrobenzene as the substrate. Diamide (4 mM), cystamine (5 mM), and N-ethylmaleimide (1 mM) increased the microsomal glutathione S-transferase activity by 3-, 2-, and 10-fold, respectively, in absence of glutathione; glutathione disulfide had no effect. In presence of glutathione, microsomal glutathione S-transferase activity was increased 10-fold by diamide (0.5 mM), but the activation of the transferase by N-ethylmaleimide or cystamine was only slightly affected by presence of glutathione. The activation of microsomal glutathione S-transferase by diamide or cystamine was reversed by the addition of dithiothreitol. Glutathione disulfide increased microsomal glutathione S-transferase activity only when membrane-bound enzyme was used. These results indicate that microsomal glutathione S-transferase activity may be regulated by reversible thiol/disulfide exchange and that mixed disulfide formation of the microsomal glutathione S-transferase with glutathione disulfide may be catalyzed enzymatically in vivo.     

Inactivation of rat pineal hydroxyindole-O-methyltransferase by disulfide-containing compounds

Rat pineal hydroxyindole-O-methyltransferase activity in crude homogenates is reduced by treatment with disulfides. Cystamine (IC50 = 128 microM) and selenocystamine (IC50 = 13 microM) are the most potent compounds tested. Reduced cystamine (cysteamine) and diaminohexane are inactive. N,N'-Diacetylcystamine, penicillamine disulfide, and glutathione disulfide are less potent or inactive; but several peptides (oxytocin, vasopressin, and arginine vasotocin) are active. Inactivation by cystamine is time- and temperature-dependent and is accelerated at higher pH. Disulfide treatment of intact pinealocytes also inactivates the enzyme. Addition of dithiothreitol during the enzyme assay completely reactivates inactivated enzyme formed by disulfide treatment of homogenates or intact cells. Rat hydroxyindole-O-methyltransferase is also inactivated in the absence of added disulfides and dissolved O2. This spontaneous inactivation is time-, temperature-, and pH-dependent and can be completely prevented, but not reversed, by dithiothreitol. In contrast to the inhibitory effects of cystamine on the rat enzyme, cystamine does not alter bovine hydroxyindole-O-methyltransferase and increases ovine hydroxyindole-O-methyltransferase activity. The bovine and ovine enzymes do not become inactive in the absence of added disulfides. Together these observations indicate that rat pineal hydroxyindole-O-methyltransferase can be inactivated by a protein thiol:disulfide exchange mechanism. This mechanism may contribute to the physiological regulation of this enzyme in the rat pineal gland but does not appear to be a common feature of pineal hydroxyindole-O-methyltransferase regulation in all species.     

Comparison of genetic and endocrine control of renin and kallikrein in mouse submandibular gland

The effects of strain, sex, hypophysectomy and hormone treatment on mouse submandibular gland renin, kallikrein, S2266 hydrolase, and BAEe esterase activities have been examined. Renin activity is determined by the $\text{Rnr}$ locus on mouse Chromosome 1. Female SWR/J mice ($\text{Rnr}$^$\text{s}$/$\text{Rnr}$^$\text{s}$) have 1000-fold higher submandibular gland renin activity than C57BL/6J mice ($\text{Rnr}$^$\text{b}$/$\text{Rnr}$^$\text{b}$). Both strains have similar kallikrein activity. Renin, BAEe esterase, and S2266 hydrolase are substantially higher in male mice compared to females of the same strain whereas kallikrein is not. Dihydrotestosterone and/or thyroxine treatment induces renin, BAEe esterase, and S2266 hydrolase in female mice with little effect on kallikrein. All four enzyme activities are profoundly reduced by hypophysectomy. Dihydrotestosterone and thyroxine are both required to restore renin, BAEe esterase, and S2266 hydrolase to induced levels. Dihydrotestosterone and.or thyroxine restores kallikrein to control levels. We conclude that renin and kallikrein in the mouse submandibular gland are under different genetic and endocrine control. In addition, the synthetic substrate S2266 is not a specific substrate for kallikrein activity in mouse submandibular gland cytosol.     

2-Methylbutyryl CoA dehydrogenase from mitochondria of Ascarissuum and its relationship to NADH-dependent 2-methylcrotonyl CoA reduction

Acyl CoA dehydrogenase and electron-transfer flavoprotein have been isolated and partially purified from mitochondria of the anaerobic nematode, $\text{Ascaris}\text{suum}$. Dehydrogenase activity was greatest with 2-methylbutyryl CoA and the relative substrate specificities of the ascarid dehydrogenase(s) differ greatly from their mammalian counterparts. It appears that the ascarid dehydrogenase functions physiologically as a reductase, catalyzing the final step in the synthesis of branched-chain fatty acids. In fact, incubations of $\text{A}\text{.}\text{suum}$ mitochondrial membranes with electron-transfer flavoprotein, 2-methylbutyryl CoA dehydrogenase, 2-methylcrotonyl CoA and NADH resulted in a substantial, rotenone-sensitive, 2-methylbutyrate synthesis. These results suggest that the ascarid electron-transport chain and at least two soluble mitochondrial proteins are involved in the NADH-dependent reduction of 2-methylcrotonyl CoA.     

Collagenase from rabbit pulmonary alveolar macrophages.

Rabbit pulmonary alveolar macrophages produce a collagenase which lyses labeled collagen gels, specifically cleaves collagen types I, II and III, is inhibited by ethylenediaminetetraacetate, cysteine, dithiothreitol and serum but is not inhibited by a serine protease inhibitor. Alveolar macrophage collagenase activity can be enhanced by $\text{in vivo}$ BCG activation, $\text{in vitro}$ latex, silica or mycobacterium activation and by $\text{in vitro}$ uncovering of latent enzymatic activity with trypsin treatment. The production of collagenase by unactivated alveolar macrophages and the presence of “latent” collagenase in culture media of alveolar macrophages are examples of significant differences between alveolar and peritoneal macrophages.     

salmonella typhimurium/enzymol.

Cysteine synthetase from Salmonella typhimurium LT-2 displays a saturation curve for sulfide identical to that obtained with uncomplexed O-acetylserine sulfhydrylase, indicating substrate inhibition with a K_m of 0.1 ± 0.017 mm and a K₁ of 0.303 ± 0.194 mm. With both l-serine and acetyl CoA, however, cysteine synthetase exhibits two intermediary plateaus in the respective saturation curves. The time course of cysteine synthetase activity when the reaction is started by adding enzyme displays a pronounced lag phase. This lag is explained as being due to the buildup of a sufficient concentration of O-acetyl-l-serine to permit binding to O-acetylserine sulfhydrylase. This conclusion is substantiated by the fact that plots of $\text{1}\text{τ}$ against concentrations of both l-serine and acetyl CoA reflect the saturation curves for these substrates. In addition, the incubation of the complex with l-serine and acetyl CoA results in the accumulation of the intermediate products of the reaction sequence, CoA and O-acetyl-l-serine. Dissociation of the multienzyme complex under these conditions was ruled out by Sephadex G-200 chromatography of the complex after incubation with assay levels of the substrates of the reaction. Aggregation of cysteine synthetase was detected using disc gel electrophoresis and confirms earlier reports [Kredich, N. M., and Tomkins, G. M. (1966) J. Biol. Chem.241, 4955–4965]. Aggregation of O-acetylserine sulfhydrylase was also detected using the same technique.     

Effect of citrate on the different reactions catalyzed by rat mammary gland acetyl CoA carboxylase

The effect of citrate on the different reactions catalyzed by rat mammary gland acetyl CoA carboxylase has been investigated. Citrate showed modest effect on the ATP-orthophosphate and ATP-ADP exchange reactions. In contrast, this tricarboxylic acid caused marked concentration-dependent stimulation of the acetyl CoA-malonyl CoA exchange reaction which was concomitant with the activation of acetyl CoA carboxylation. The data obtained are consistent with the suggestion that activation by citrate of the overall forward reaction (malonyl CoA synthesis) primarily reflects enhancement of the carboxyltransferase half-reaction catalyzed by rat mammary gland acetyl CoA carboxylase.     

3-Hydroxy-3-methylglutaryl CoA reductase of Hevea latex: The occurrence of a heat-stable activator in the C-serum

The effect of the C-serum (the cytosol) on the activity of 3-hydroxy-3-methylglutaryl CoA reductase in the latex of $\text{Hevea}\text{brasiliensis}$ was investigated. Depending on the clone from which the latex was obtained, the C-serum was found to depress or activate or have little effect on the enzyme activity. Boiling the C-serum however, resulted in a consistent activation effect in all the clones examined. Optimal activation was obtained with 20 μl boiled C-serum. Dialysis or EDTA (40 mM) treatment of the boiled C-serum did not diminish the activation effect. Although not essential, dithiothreitol complemented the activation effect of the boiled C-serum and the optimal concentration was 10 mM. Trypsin digestion of the boiled C-serum resulted in the complete loss of the activation effect. The activator in the boiled C-serum was salted out by ammonium sulphate at 25 – 100% saturation. Hevein had no effect on reductase activity.     

Acetate metabolism by tissues of the rabbit

Acetyl CoA synthetase (E.C.6.2.1.1) and acetyl CoA hydrolase (E.C.3.1.2.1) activities were assayed in sub-cellular fractions of rabbit liver, heart and kidney homogenates. The intracellular location of acetyl CoA hydrolase was predominantly mitochondrial in all tissues, whereas that for acetyl CoA synthetase varied between the tissues studied. The relationship between location of enzyme activity and metabolism of acetate in different tissues is discussed.     

Preparation and biological activity of taxol acetates

Synthesis and biological activity of 2′-acetyltaxol and 7-acetyltaxol are reported. Activity is measured $\text{in}\text{vivo}$ by cytotoxicity toward the macrophage-like cell line J774.2, and $\text{in}\text{vitro}$ by promotion of microtubule assembly in the absence of exogenous GTP. Addition of an acetyl moiety at C-2′ results in loss of $\text{in}\text{vitro}$ activity but not cytotoxicity. The properties of 7-acetyltaxol are similar to those of taxol in its effects on cell replication and on $\text{in}\text{vitro}$ microtubule polymerization. Therefore a free hydroxyl group at C-7 is not required for $\text{in}\text{vitro}$ activity and this position is available for structural modifications.     

Activation of pineal and brain acetyl-COA hydrolase by cystamine: an apparent case of disulfide exchange.

Rat pineal acetyl-CoA hydrolase was activated about 5-fold by cystamine treatment (30 mM) at pH 6.8 and 10-fold at pH 8.5. Six other disulfides were found to be ineffective or to produce a small activation. Cystamine activation was not reversed when free cystamine was removed, but was reversed by treatment with DTT. Analysis of other tissues indicated acetyl-CoA hydrolase from rat brain, sheep pineal gland and chicken pineal gland could also be activated by cystamine. In contrast, cystamine activation of rat liver acetyl-CoA hydrolase was not seen.     

Low molecular weight mitogenic factor produced by BRL-3A cultured rat liver cells

A new mitogenic factor has been isolated from medium conditioned by BRL-3A rat liver cells. The factor has been partially purified by a two step procedure involving ion exchange chromatography on Dowex 50 followed by gel filtration chromatography on Sephadex G-75 in 1 M acetic acid. The factor is eluted from the Sephadex G-75 column in the low molecular weight region, behin three peaks of multiplication stimulating activity. The factor is inactivated by treatment with trypsin and dithiothreitol, suggesting that it is a peptide that contains a disulfide linkage. Unlike multiplication stimulating activity, the new factor only weakly stimulates DNA synthesis in quiescent chick fibroblasts, whereas it strongly stimulates DNA synthesis in quiescent NIL8 hamster cells, $\text{BALB}\text{c}$ 3T3 cells, and IMR-90 human fibroblasts.     

A mutant of Escherichia coli with altered inducer specificity for the fad regulon

A novel regulatory mutant of the fatty acid degradation ($\text{fad}$) regulon of $\text{Escherichia coli}$ was isolated. This mutant, D-2, was induced to synthesize the fatty acid β-oxidation enzymes during growth on decanoate and laurate whereas the wild type strain was induced only when fatty acids with a chain length greater than 12 carbon atoms were present in the growth medium. The fatty acid specificity of the acyl CoA synthetase was also changed in strain D-2. The data are consistant with the hypothesis that acyl CoA's themselves are the inducers of the $\text{fad}$ regulon and suggest that strain D-2 may synthesize an altered $\text{fad}$ regulatory protein. The results also suggest that the acyl CoA synthetase may possess regulatory as well as enzymatic activity.     

Fatty acid utilization and purine nucleotide binding in brown adipose tissue of genetically obese (ob/ob) mice

The activities of the main enzymes involved in fatty acid utilization i.e. palmitoyl CoA synthetase as well as peroxisomal and mitochondrial β-oxidation were measured in brown adipose tissue homogenates of lean and $\text{ob}$/$\text{ob}$ mice kept at 23°C or acclimated at 4°C. The proton conductance pathway, i.e. the number of purine nucleotide (GDP) binding sites and the percentage of 32,000 polypeptide in brown adipose tissue mitochondria were also measured. In the if$\text{ob}$/$\text{ob}$ mice at 23° C, the specific activities of the palmitoyl CoA synthetase and of the β-oxidation as well as the number of GDB binding sites were lower than in the lean mice by 26%, 43% and 37%, respectively. The percentage of 32, 000 polypeptide, however, was the same in both groups. In the $\text{ob}$/$\text{ob}$ mice at 23° C, the lower homogenate β-oxidation specific activity was due to the fact that the peroxisomal and mitochondrial specific activities were 44% and 37% lower, respectively. Cold acclimation at 4° C was found to cause an increase of the palmitoyl CoA synthetase specific activity, of the palmitoyl CoA synthetase and peroxisomal β-oxidation total activities and of the number of GDP binding sites, in both lean and $\text{ob}$/$\text{ob}$ mice. Cold acclimation increased the percentage of 32,000 polypeptide in the $\text{ob}$/$\text{ob}$ mice only.     

The effect of long chain fatty acyl CoA esters on the adenine nucleotide translocase and myocardial metabolism.

The adenine nucleotide translocase, the transport protein for ADP and ATP, located in the inner mitochondrial membrane is an important site for the regulation of cell metabolism. Inhibition of the adenine nucleotide translocase by long chain fatty acyl CoA esters demonstrated $\text{in}$$\text{vitro}$ may also occur $\text{in}$$\text{vivo}$ when the complete oxidation of fatty acids by the myocardium has been compromised during ischemia. Reversal of this biochemical lesion may be of benefit in the preservation of the ischemic myocardium.     

Evidence against the presence of cyclic AMP and related enzymes in selected strains of Bacteroides fragilis

Cyclic AMP was not detected in whole cells, expended culture medium or culture supernatant fluid of selected strains of $\text{Bacteroides fragilis}$. Adenyl cyclase and c-AMP phosphodiesterase activities were also not detected in cell extracts of $\text{B. fragilis}$. The exogenous addition of dibutyryl-c-AMP or sodium cholate to cultures of $\text{B. fragilis}$ growing on lactose did not significantly affect the specific activity of β-galactosidase measured in cell extracts of this organism. No diauxic growth pattern could be demonstrated in a chemically defined medium containing 5 mM glucose + 28 mM lactose.     

Bile acid biotransformation rates of selected gram-positive and gram-negative intestinal anaerobic bacteria.

Treatment of whole cell suspensions of $\text{Eubacterium aerofaciens}$ and $\text{Bacteroides fragilis}$ with lysozyme resulted in a marked increase (>100-fold) in the rates of biotransformation of cholate to 7-ketodeoxycholate (7-KD) in the former but only a 2-fold increase in the latter bacterium. In $\text{B. fragilis}$ the total activity of both NAD-dependent 7-α-hydroxysteroid dehydrogenase (7-α-OHSDH) and bile salt hydrolase (BSH) increase markedly during the stationary growth phase. Both enzymes were found in the spheroplast lysate and the Triton-soluble washed membrane fractions but only BSH was found in the spheroplast medium.     

Soluble and membrane-bound thiamine-binding proteins from Saccharomyces cerevisiae

Previous communications from this laboratory have indicated that there exists a thiamine-binding protein in the soluble fraction of Saccharomyces cerevisiae which may be implicated to participate in the transport system of thiamine in vivo.In the present paper it is demonstrated that both activities of the soluble thiamine-binding protein and thiamine transport in S. cerevisiae are greatest in the early-log phase of the growth and decline sharply with cell growth. The soluble thiamine-binding protein isolated from yeast cells by conventional methods containing osmotic shock treatment appeared to be a glycoprotein with a molecular weight of 140 000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The apparent $\text{K}{}_{\mathrm{<mtext>d</mtext>}}$ of the binding for thiamine was 29 nM which is about six fold lower than the apparent $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ (0.18 μM) of thiamine transport. The optimal pH for the binding was 5.5, and the binding was inhibited reversibly by 8 M urea but irreversibly by 8 M urea containing 1% 2-mercaptoethanol. Several thiamine derivatives and the analogs such as pyrithiamine and oxythiamine inhibited to similar extent both the binding of thiamine and transport in S. cerevisiae, whereas thiamine phosphates, 2-methyl-4-amino-5-hydroxymethylpyrimidine and $\text{O-}\text{benzoylthiamine}$ disulfide did not show similarities in the effect on the binding and transport in vivo. Furthermore, it was demonstrated by gel filtration of sonic extract from the cells that a thiamine transport mutant of S. cerevisiae (PT-R₂) contains the soluble binding protein in a comparable amounts to that in the parent strain, suggesting that another protein component is required for the actual translocation of thiamine in the yeast cell membrane. On the other hand, the membrane fraction prepared from S. cerevisiae showed a thiamine-binding activity with apparent $\text{K}{}_{\mathrm{<mtext>d</mtext>}}$ of 0.17μM at optimal pH 5.0 which is almost the same with the apparent $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ for the thiamine transport system. The membrane-bound thiamine-binding activity was not only repressible by exogenous thiamine in the growth medium, but as well as thiamine transport it was markedly inhibited by both pyrithiamine and $\text{O-}\text{benzoylthiamine}$ disulfide. In addition, it was found that membrane fraction prepared frtom PT-R₂ has the thiamine-binding activity of only 3% of that from the parent strain of S. cerevisiae.These results strongly suggest that membrane-bound thiamine-binding protein may be directly involved in the transport of thiamine in S. cerevisiae.