Effects Of Various Metabolites Research Articles

Screening of liver protective effect of herbal hepatoprotective product in ethanol induced hepatotoxicity in Wister rats

Background: liver is highly susceptible to the toxic and adverse effects of various metabolites and xenobiotics such as alcohol etc. Alcohol abuse leads to hepatotoxicity that is presented in the form of Alcoholic Liver Disease. Aims and Objectives: The present study was conducted to evaluate hepatoprotective activity of polyherbal formulation. The test drug was studied in comparison with marketed formulations in ethanol induced hepatotoxicity in wistar albino rats. Methods: Total 7 groups of animals were studied comparatively to evaluate efficacy of various formulations. Results: It was found that all the formulations tested including all the dosages of Polyherbal Capsule significantly reduced levels of SGOT (Serum glutamic oxaloacetic transaminase), SGPT (Serum glutamate pyruvate transaminase), Alkaline phosphatase (ALP) and Total Bilirubin when compared to ethanol group. There was significant increase in total protein level in Ariliv Tablet, Silymarin and marketed formulation groups. Also, all the formulations tested effectively preserved the structural integrity of the hepatocellular membrane and liver cell architecture damaged by ethanol. When compared between formulation groups there was no statistical significant difference. Conclusion: It can be concluded that Polyherbal Capsule possesses hepatoprotective activity in ethanol induced hepatotoxicity in rats. Polyherbal Capsule can be effectively used in hepatitis caused due to alcohol.

The past, present, and future of research on neuroinflammation-induced mild cognitive impairment: A bibliometric analysis.

BackgroundMild cognitive impairment (MCI) is a precursor to dementia, and neuroinflammation in the brain is thought to be one of the main pathogenic mechanisms of MCI. However, the underlying neurobiological mechanisms have not been fully explored. The purpose of this study was to establish a visual model map of the articles in the field of neuroinflammation-induced MCI over the past 11 years to reveal the research hotspots and predict the future development trends in this field, which will help to promote the research and development for MCI.MethodsThe “neuroinflammation” and “mild cognitive impairment” were used as search terms, and literature about neuroinflammation-induced MCI published between 2011 and 2021 was collected from the Web of Science. CiteSpace and VOSviewer were used to create visual model maps, and assess collaboration among different authors, countries, and institutions. Finally, the current research hotspots and future research directions were analyzed by using high-frequency keywords analysis and co-cited reference burst analysis.ResultsA total of 226 articles were retrieved. The number of publications in neuroinflammation-induced MCI shows an upward trend. Since 2018, the number of papers published in this field has increased significantly, with an average of more than 100 published each year. The United States had the highest literature production and the number of cited journals in this research area, and the National Institute on Aging was the most productive research institution. Brooks D.J. and Heneka M.T. had the highest number of publications and had the highest frequency of co-citations. The co-cited references revealed the evolution of the research themes, and the current studies are mainly focused on the effects of various metabolites on the control of microglial activation. “Cerebrospinal fluid,” “mouse model,” “tau,” “microglial activation,” “astrocytes,” and “TREM2” were the current high-frequency and emerging keywords.ConclusionResearch on neuroinflammation-induced MCI is burgeoning, and the close collaboration with different nations and institutions need to be further strengthened. Current research hotspots are focused on the effects of various metabolites on microglia activation. Future studies should focus on how to regulate the phenotypes of microglia and astrocyte to reduce neuroinflammation and treat MCI.

Exploring the effect of variable enzyme concentrations in a kinetic model of yeast glycolysis.

Metabolism is one of the best studied fields of biochemistry, but its regulation involves processes on many different levels, some of which are still not understood well enough to allow for quantitative modeling and prediction. Glycolysis in yeast is a good example: although high-quality quantitative data are available, well-established mathematical models typically only cover direct regulation of the involved enzymes by metabolite binding. The effect of various metabolites on the enzyme kinetics is summarized in carefully developed mathematical formulae. However, this approach implicitly assumes that the enzyme concentrations themselves are constant, thus neglecting other regulatory levels--e.g. transcriptional and translational regulation--involved in the regulation of enzyme activities. It is believed, however, that different experimental conditions result in different enzyme activities regulated by the above mechanisms. Detailed modeling of all regulatory levels is still out of reach since some of the necessary data--e.g. quantitative large scale enzyme concentration data sets--are lacking or rare. Nevertheless, a viable approach is to include the regulation of enzyme concentrations into an established model and to investigate whether this improves the predictive capabilities. Proteome data are usually hard to obtain, but levels of mRNA transcripts may be used instead as clues for changes in enzyme concentrations. Here we investigate whether including mRNA data into an established model of yeast glycolysis allows to predict the steady state metabolic concentrations for different experimental conditions. To this end, we modified an established ODE model for the glycolytic pathway of yeast to include changes of enzyme concentrations. Presumable changes were inferred from mRNA transcript level measurement data. We investigate how this approach can be used to predict metabolite concentrations for steady-state yeast cultures at five different oxygen levels ranging from anaerobic to fully aerobic conditions. We were partly able to reproduce the experimental data and present a number of changes that were necessary to improve the modeling result.

S-adenosyl-L-methionine is an effector in the posttranscriptional autoregulation of the cystathionine gamma-synthase gene in Arabidopsis.

Cystathionine gamma-synthase, the first committed enzyme of methionine biosynthesis in higher plants, is encoded by the CGS1 gene in Arabidopsis thaliana. We have shown previously that the stability of the CGS1 mRNA is negatively regulated in response to methionine application [Chiba, Y., Ishikawa, M., Kijima, F., Tyson, R. H., Kim, J., Yamamoto, A., Nambara, E., Leustek, T., Wallsgrove, R. M. & Naito, S. (1999) Science 286, 1371-1374]. To determine whether methionine itself is the effector of the CGS1 exon 1-mediated posttranscriptional regulation, we carried out transfection experiments. The results suggested that, rather than methionine, S-adenosyl-L-methionine (AdoMet), or one of its metabolites, acts as the effector of this regulation. To further identify the actual effector, we exploited the wheat germ in vitro translation system. The effects of various metabolites and analogs of AdoMet were tested by using RNA carrying a CGS1 exon 1-reporter fusion. These tests identified AdoMet as the effector of this regulation. S-adenosyl-L-ethionine, an analog of AdoMet, also had effector activity. A. thaliana mto1 mutants, which are deficient in this regulation, showed a much reduced response to AdoMet in vitro, with a leaky allele showing a less reduced response. RNA translated in vitro in the presence of AdoMet contained a 5'-truncated RNA species, similar to the one that we previously suggested was an in vivo degradation intermediate of CGS1 mRNA. Together, the results show that the basic reactions of CGS1 exon 1-mediated posttranscriptional regulation occur in the wheat germ in vitro translation system, and that AdoMet acts as the effector.

Precursor and Effector Dependency of Lipid Synthesis in Amyloplasts Isolated from Developing Maize and Wheat Endosperm

Recently, we developed a method for the isolation of amyloplasts from maize endosperm. Here we describe a new protocol for the isolation of intact and pure amyloplasts from developing wheat endosperm. The precursor and effector dependencies of fatty-acid synthesis were analysed for both types of cereal amyloplasts. Both wheat and maize-endosperm amyloplasts used [214C]pyruvate with the greatest efficiency for the synthesis of fatty acids. Malate was not converted to fatty-acids. The effects of various metabolites upon both pyruvate- and acetate-dependent fatty-acid synthesis were compared for maize or wheat plastids. In all cases, fatty-acid synthesis was dependent upon the additional presence of ATP in the incubation medium. [214C]pyruvate-driven fatty-acid synthesis in isolated wheat amyloplasts was not totally dependent upon the additional presence of reduced pyridine dinucleotide (NADH) in the incubation medium. Both pyruvate- and acetate-dependent fatty-acid synthesis in cereal amyloplasts could be stimulated to maximal rates by exogenous glucose 6-phosphate indicating an interaction of the oxidative pentose-phosphate pathway and fatty-acid synthesis.

Insect induced plant galls in tissue culture

Plant tissue culture enabling the assessment of excised organ tissues and cells and the effect of various metabolites and gall and normal tissues are discussed with reference to insect induced plant galls. In particular the stem and rachis galls ofProsopis cineraria caused by a chalcid andLobopteromyia prosopidis, stem gall ofEmblica officinalis Gaertn induced by a Lepidopteran,Betousa stylophora Swinhoe, stem gall ofZizyphus mauritiana induced by a mite,Eriophyes cernuus, thePhylloxera gall on grape and many others are discussed.

Mechanism of pyruvate inhibition of plant pyruvate dehydrogenase kinase and synergism with ADP

The effects of various metabolites on pyruvate dehydrogenase (PDH) kinase-catalyzed inactivation of the pyruvate dehydrogenase complex (PDC) were studied in extracts of mitochondria purified from green leaf tissue of Pisum sativum L. Pyruvate was an uncompetitive inhibitor of PDH kinase with respect to ATP whereas ADP was a competitive inhibitor. In the absence of pyruvate a fivefold excess of ADP over ATP was required to inhibit PDH kinase, however, in the presence of pyruvate much lower ADP concentrations were required. Inhibition of PDH kinase by pyruvate and ADP was synergistic and the addition of ADP changed pyruvate from an uncompetitive inhibitor to a noncompetitive inhibitor. This result indicates that pyruvate acts as a “dead-end” inhibitor, binding to the PDH kinase—ADP reaction intermediate. Evidence is also presented that inhibition by pyruvate in the presence of thiamine pyrophosphate is due to the formation of hydroxyethyl thiamine pyrophosphate. The results are discussed in terms of the regulation of PDC activity by pyruvate and ADP during periods of increased demand for carbon skeleton biosynthesis by way of the tricarboxylic acid (TCA) cycle despite constraints imposed on TCA cycle flux by a high ATP/ADP ratio.

Nucleotide modulation of the activity of rat heart ATP-sensitive K+ channels in isolated membrane patches.

1. We have measured the ATP dependence of KATP channel activity, and the effect of various metabolites on this relationship, in inside-out membrane patches isolated from rat ventricular myocytes. 2. The inhibition of KATP channel activity by ATP could be described as a sigmoid function of [ATP] with a Hill coefficient (HATP) of 2 and a half-maximal inhibition at an ATP concentration (Ki, ATP) of 25 microM, in the presence of 0 mM, or 0.5 mM, total [Mg2+]. The non-hydrolysable ATP analogue, AMP-PNP, also inhibited the channel with Ki, AMP-PNP = 60 microM and HAMP-PNP = 2. 3. Acidosis caused a small, but significant, increase in Ki, ATP from 25 microM at pH 7.25 to 50 microM at pH 6.25, but phosphate and lactate were without effect (at 20 mM) on channel activity. 4. In the absence of ATP or Mg2+, ADP3- inhibited channel activity with Ki, ADP = 275 microM, and HADP = 1.2. Other purine and pyrimidine triphosphates, diphosphates and monophosphates also inhibited the channel with apparent order of inhibitory effectiveness ATP greater than AMP-PNP greater than ADP greater than CTP greater than GDP = AMP = ITP. 5. In the absence of Mg2+, but in the presence of 40 microM-ATP, channel inhibition by GTP, ITP, CTP, GDP, ADP or AMP was additive with inhibition by ATP. 6. In the presence of 0.5 mM-Mg2+ and 40 microM-ATP, inhibition by GTP, GMP and AMP was still additive with inhibition by ATP. The diphosphates ADP and GDP, however, paradoxically increased channel activity in the presence of ATP. This increase in channel activity appeared to result from a competitive increase in Ki, ATP, MgADP did not appear to cause any inhibition of channel activity. 7. We conclude that, in cardiac tissue, KATP channels are regulated by [ATP], and that this regulation is sensitive to other intracellular nucleotides, Mg2+, and pH, but not to phosphate or lactate. A simple, interactive two binding-site model is consistent with the nucleotide-dependent regulation that we observe.

Quantitation of the interaction between citrate synthase and malate dehydrogenase.

Formation of a bienzyme complex of pig heart mitochondrial malate dehydrogenase and citrate synthase in a buffered system is demonstrated by means of a covalently attached fluorescent probe to citrate synthase. Assuming 1:1 stoichiometry of the enzymes in the complex, an apparent dissociation constant of 10(-6) M was calculated from fluorescence anisotropy measurements. The effect of various metabolites on the interaction was tested. NAD+, oxalacetate, citrate, ATP, and L(-)- or D(+)-malate had no effect on the association of the two enzymes, whereas alpha-ketoglutarate increased and NADH decreased it. The interaction of mitochondrial citrate synthase with cytosolic malate dehydrogenase was found to be much weaker, whereas interaction of citrate synthase with another cytosolic enzyme, aldolase, could not be detected. In kinetic experiments, the activation of malate dehydrogenase by citrate synthase was observed. The effect of pyridine nucleotides and alpha-ketoglutarate is discussed in relation to the direction of the metabolic flow of oxalacetate.

Effects of various metabolites on two phosphoglucomutase allozyme activities from Drosophila melanogaster.

The effects of various metabolites on the two most common phosphoglucomutase allozymes (PGMA and PGMB) in Drosophila melanogaster have been investigated in vitro. 2,3-Diphosphoglycerate (2,3DPG) inhibited PGMA and PGMB to the same degree in the presence of 25 microM glucose-1,6-diphosphate (G1,6P2). However a higher concentration of G1,6P2 partially reversed the inhibition of PGMA exerted by 2,3DPG, so that in the presence of 150 microM G1,6P2 the inhibition of PGMA was half that of PGMB at pH 6.0. Glycerol-3-phosphate (G3P) had no significant effect at pH 7.4 but exerted an activating effect at pH 6.0 which was more pronounced in the case of PGMB. ATP, citrate, and fructose-1, 6-diphosphate (F1,6P2) inhibited both PGMA and PGMB. The differences found in vitro between these two allozymes can have a significant impact on in vivo function and, therefore, on the maintenance of PGM polymorphism in experimental populations of D. melanogaster studied in the laboratory.

The purification and properties of human liver ketohexokinase. A role for ketohexokinase and fructose-bisphosphate aldolase in the metabolic production of oxalate from xylitol.

Ketohexokinase (EC 2.7.1.3) was purified to homogeneity from human liver, and fructose-bisphosphate aldolase (EC 4.1.2.13) was partially purified from the same source. Ketohexokinase was shown, by column chromatography and polyacrylamide-gel electrophoresis, to be a dimer of Mr 75000. Inhibition studies with p-chloromercuribenzoate and N-ethylmaleimide indicate that ketohexokinase contains thiol groups, which are required for full activity. With D-xylulose as substrate, ketohexokinase and aldolase can catalyse a reaction sequence which forms glycolaldehyde, a known precursor of oxalate. The distribution of both enzymes in human tissues indicates that this reaction sequence occurs mainly in the liver, to a lesser extent in the kidney, and very little in heart, brain and muscle. The kinetic properties of ketohexokinase show that this enzyme can phosphorylate D-xylulose as readily as D-fructose, except that higher concentrations of D-xylulose are required. The kinetic properties of aldolase show that the enzyme has a higher affinity for D-xylulose 1-phosphate than for D-fructose 1-phosphate. These findings support a role for ketohexokinase and aldolase in the formation of glycolaldehyde. The effect of various metabolites on the activity of the two enzymes was tested to determine the conditions that favour the formation of glycolaldehyde from xylitol. The results indicate that few of these metabolites affect the activity of ketohexokinase, but that aldolase can be inhibited by several phosphorylated compounds. This work suggests that, although the formation of oxalate from xylitol is normally a minor pathway, under certain conditions of increased xylitol metabolism oxalate production can become significant and may result in oxalosis.

Role of pyruvate kinase, phosphoenolpyruvate carboxykinase, malic enzyme and lactate dehydrogenase in anaerobic energy metabolism ofTubifex spec

1. During anaerobic exposure ofTubifex, lactate and alanine increase only within the first 24 h, while concentrations of succinate, propionate and also acetate continually increase under prevailing anaerobic conditions. Enzymes involved in anaerobic energy metabolism were isolated, and the effects of various metabolites and inorganic compounds on their catalytic properties studied. 2. The specific activities of the cytosolic enzymes LDH, PK, MDH, and PEPCK, and of mitochondrial malic enzyme and MDH are high. 3. Under conditions of high HCO3− (HCO3−+CO2 system), PEPCK is maximally active while PK is inhibited. 4. The catalytic properties of mitochondrial malic enzyme indicate that in vivo this enzyme operates in the direction of malate decarboxylation. 5. The cytosolic oxidoreductases LDH and MDH were examined with regard to the maintenance of redox state. Function of MDH is only subject to substrate availability, while the enzyme-substrate affinity of LDH might be affected by pH to a limited extent. 6. The data support the conclusion that total CO2, fructose-1,6-diphosphate concentration, the adenylate energy charge, and-only to a limited extent-the intracellular pH are regulatory signals which govern PEP metabolism inTubifex.

Regulation of pyruvate kinases from Fusarium oxysporum.

Two types of pyruvate kinases were found in Fusarium oxysporum. One type (inducible) was present mainly during the early stages of growth on glucose or sucrose and displayed Michaelis-Menten kinetics with respect to phosphoenolpyruvate and adenosine diphosphate. The major type (constitutive) was present under all conditions of growth and displayed in the absence of potassium ions, a sigmoidal substrate saturation curve when phosphoenolpyruvate was used as the variable substrate. In the presence of potassium ions the saturation curve for phosphoenolpyruvate exhibits a plateau at half-maximal velocity. The effects of various metabolites on the activity of the inducible and constitutive kinases were also studied. Fructose-1,6-diphosphate, cyclic AMP, acetyl CoA, tryptophan, and phenylalanine had no effect on the activity of the enzymes. Citrate was a potent inhibitor of the constitutive pyruvate kinase activity and increased the sigmoidicity of the saturation curve for phosphoenolpyruvic acid. In the presence of K+, the bimodal plot observed in the absence of citrate gradually changed to a hyperbolic shape as the concentration of citric acid was increased. In the presence of K+ and ADP as the variable substrate citric acid converted the hyperbolic plot to a sigmoidal one. Citrate had no effect on the inducible enzyme.

Biological significance of the metabolism of androgens in the central nervous system

Several testosterone-dependent actions of the mammalian CNS may be mediated by its metabolites. Regional distribution, selective retention, and further in vivo and in vitro metabolism of androgens in the pituitary and brain of several species are well known. Male sexual behavior and gonadotropin secretion were used as typical neuroendocrine androgen regulated functions. Since testosterone and androstenedione can be biotransformed to at least five neutral metabolites besides phenolic derivatives, a correlation between androgen metabolism in the CNS and the expression of the activity of the enzymatically formed androgen metabolites was made. It was found that non-aromatizable androgens elicited weak, if any, male copulatory behavior, suggesting that estrogens may play an important role in this function, although antiestrogens can not prevent the androgen-induced behavior and estrogens administered in low dosages per se are ineffective. From another series of experiments it was concluded that the expression of male sexual behavior may result either from unmetabolized testosterone or by the combined effects of 5α-ring A reduced metabolites [Dihydrotestosterone] and estrogens (E2), whereas the gonadotropin inhibition mechanism does not require androgen aromatization at least in the rat. These studies strongly suggest that the androgen mechanism of action of the CNS may be the result of simultaneous effect of various metabolites formed either peripherally or at brain level.

The synthesis of glutamate and the control of glutamate dehydrogenase in pea mitochondria

The synthesis of glutamate from α-oxoglutarate and NH 4 + by pea seedling mitochondria has been demonstrated under certain defined but non-physiological conditions. Malate acts as a hydrogen donor for the synthesis of glutamate but isocitrate is more effective, whilst succinate, in the presence or absence of ATP, is a poor donor of hydrogen. Glutamate dehydrogenase has been purified from pea mitochondria and from the cytosol. The similarities between the two preparations are interpreted to mean that the soluble glutamate dehydrogenase is released from the mitochondria during isolation. The kinetics of the mitochondrial enzyme and the effect of various metabolites on its activity have been examined. The results are discussed in relation to the proposed role of this enzyme and it is suggested that the ratio NADH-NAD + may play a role in the control of glutamate metabolism.

Role of fatty acid metabolism on renal transport of [formula omitted]in vitro

1. 1. The accumulation of p- aminohippurate and oxygen consumption in cortical slices prepared from rabbit kidneys were measured in the presence of various fatty acids and inhibitors of fatty acid metabolism ((+)-palmitylcarnitine and 2-bromopalmitate). Furthermore, 14CO 2 production from radioactive labelled metabolites were estimated in the (+)-palmitylcarnitine and bromopalmitate experiments. 2. 2. Palmitate, stearate, and oleate (bound to human albumin) were all readily oxidized by the renal tissue and gave rise to a significant stimulation of p- aminohippurate accumulation which was enhanced approx. 60% at 1 mM fatty acids in the incubation medium. However, at a fatty acid concentration of 5 mM the p- aminohippurate accumulation was reduced relative to that found at 1 mM. In accordance with previous reports octanoate (1 and 2 mM) drastically inhibited the uptake of p- aminohippurate . 3. 3. Addition to the medium of (+)-palmitylcarnitine or 2-bromopalmitate caused a considerable decrease of p- aminohippurate accumulation and of 14CO 2 formation from [ 14C]palmitate while oxygen consumption was almost unaffected. The unchanged oxygen consumption may be explained by a compensatory increase of carbohydrate metabolism, since a pronounced enhancement of 14CO 2 production from [ 14C]glucose was observed. 4. 4. Evidence based on the inhibitor-reversing effect of various metabolites support the view that in contrast to (+)-palmitylcarnitine, 2-bromopalmitate does not have a significant direct inhibitory effect on the p- aminohippurate transport through the cell membrane. 5. 5. It is concluded that the metabolism of physiological long-chain fatty acids is necessary for accumulation of p- aminohippurate in vitro. However, at high concentrations a direct inhibitory action of the fatty acids on the transport of p- aminohippurate is apparent. It is suggested that the more pronounced inhibition of p- aminohippurate accumulation by short-chain fatty acids is due to a higher degree of water solubility of these compounds compared with that of the long-chain fatty acids.

Inhibition of maize leaf phosphopyruvate carboxylase by oxaloacetate

Phosphopyruvate carboxylase was purified 60-fold from maize leaf lamina and the effect of various metabolites on the activity of the enzyme examined. Oxaloacetate was the only compound found that inhibited the enzyme at physiological concentrations; 50% inhibition occurring at 0.25 mM oxaloacetate. The significance of this inhibition in relation to regulation of the C 4-dicarboxylic acid pathway of photosynthesis is discussed.

Effects of cortisol on the levels of metabolites and enzymes controlling glucose production from pyruvate

Starvation and cortisol treatment of rats result in an almost 2-fold increase in the glucogenic capacity of kidney cortex slices when supplemented with an excess of pyruvate or succinate. A rise of both pyruvate carboxylase and phosphoenolpyruvate (PEP) carboxykinase was considered to be the cause of the increased glucogenic capacity observed. This assumption could be supported by assays of pyruvate carboxylase and PEP carboxykinase under the influence of cortisol and after starvation: the activities of both enzymes were found to be elevated in the liver 6 hr after treatment of rats with a single dose of cortisol and in starved animals. The activities of both enzymes from kidney behaved in a similar fashion. ▪ Studies on the intracellular location of pyruvate carboxylase revealed that 30–50% of the total activity present in liver and kidney may be solubilized by isotonic solutions supplemented with sodium or potassium ions. Acetyl-CoA can substitute for these cations. Glutamic dehydrogenase, an enzyme exclusively located in the mitochondria, is solubilized to 3% only by these treatments. This behavior of pyruvate carboxylase favors an extramitochondrial location of part of this enzyme which is apparently bound to the external surface of the mitochondrion or other subcellular particulate fractions. Assays of the activities of the soluble and the mitochondrial pyruvate carboxylase after administration of cortisol support a regulation of gluconeogenesis by control of the extramitochondrial enzyme levels. The stimulation of gluconeogenesis by glucocorticoids independent of de novo synthesis of enzymes in liver was studied. Two possible mechanisms were investigated: activation of glucogenic enzymes, and inhibition of enzymes involved in glucose degradation by metabolites. Activation of pyruvate carboxylase, a key enzyme of gluconeogenesis, could be supported by assays of acetyl-CoA in livers of rats with a sensitive isotope assay. Within 3–6 hr after treatment of adrenalectomized rats with a single dose of cortisol, the levels of acetyl-CoA, an activator of pyruvate carboxylase, were significantly elevated when compared with untreated animals. A negative control of glycolysis under the influence of cortisol was supported by assays of glucose-6-phosphate in liver. Concomitant with acetyl-CoA, glucose-6-phosphate levels were also elevated. Inhibition of phosphofructokinase by citrate as the cause of the glucose-6-phosphate rise could be excluded. The mechanism involved has still to be elucidated. An additional negative control of glucose degradation under the influence of glucocorticoids could be supported by a study of the effects of various metabolites on the activity of a 100-fold purified pyruvate kinase from liver. Among 32 metabolites investigated, alanine proved to be a potent inhibitor of the enzyme from liver. The inhibitory action of alanine was evident in a concentration range such as has been found in liver. Amino acid mobilization under cortisol may thus also control the glucogenic capacity of liver. Glycogenesis, fixation of CO 2 into glycogen, and the rise of the various metabolites after cortisol treatment could be blocked by actinomycin D. This finding is in agreement with an enzyme induction in adipose tissue as the cause of the cortisol-dependent mobilization of fatty acids and the concomitant rise of the metabolites investigated. The dose of actinomycin necessary for the suppression of the latter effects of the hormone, however, was found to be twice (400 μg) the dose which completely blocks de novo synthesis of enzymes in liver (150–200 μg). In order to obtain experimental evidence for a primary action in the control of enzyme synthesis, the effect of glucocorticoids on CO 2-fixation and on the activities of pyruvate carboxylase was studied in vitro. Since kidney cortex slices, in contrast to liver slices, did not show leakage of pyruvate carboxylase activities on prolonged incubation, this tissue was chosen for studies in vitro. Incubation of kidney cortex slices from adrenalectomized rats with cortisol or dexamethasone ( 2 × 10 −5 m ) resulted in a significant increase in both the activity of pyruvate carboxylase and CO 2-fixation into glucose and into di- and tricarboxylic acids. Puromycin completely abolished this effect in vitro. Reproducibility of the effects in vitro depended on the presence of an amino acid mixture. This finding is in accord with a “permissive” role of glucocorticoids in the control of enzyme synthesis, as suggested by others.

Protein synthesis in growing rat tissues: I. Effect of various metabolites and inhibitors on phenylalanine incorporation by brain and liver ribosomes

Experiments were performed to study the response of rat-brain and rat-liver ribosomes to various metabolites and inhibitors that are known to affect amino acid incorporation by interfering with one or more steps in the sequence of protein biosynthesis. Some quantitative and qualitative differences were noted in the effects of these compounds depending on the tissue source of the ribosomes, the age of the tissue and whether the amino acid was incorporated by ribosomes into protein or into poly-U-directed polyphenylalanine. Chloramphenicol slightly enhanced the incorporation into brain ribosomal protein while it depressed the incorporation into polyphenylalanine, the extent of this depression being dependent upon the age of the tissue. The results suggest that this antibiotic acts by inhibiting the attachment of mRNA to ribosomes, but it has no effect after this attachment has taken place. The oxidized form of glutathione (GSSG) and cystine were found to be very inhibitory when added to the reaction mixture. This inhibition was not counteracted by simultaneous additions of NAD +, NADP +, NADH, or NADPH. On the other hand, these coenzymes themselves produced inhibition of phenylalanine incorporation. Reaction mixtures containing the inhibitory-sulfur compounds, did not accumulate phenylalanyl sRNA. On the contrary, incorporation into sRNA was inhibited by these compounds and this inhibition corresponded closely with their inhibition of protein synthesis. This is taken to indicate that the primary effect of these compounds on the incorporation mechanism consists in their action on the amino acid activation step.

Some effects of electrical stimulation and exogenous metabolites on the contractile activity and the ultrastructure of the radula-muscle of Buccinum undatum.

The effect of various metabolites on the contractile pattern of the radulamuscle of Buccinum undatum was recorded. Its ultrastructure was studied after varying periods of spontaneous and electrically induced work.