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Biomedical subjects

T Ramasarma

Publications and source records attributed to T Ramasarma.

At least 145 records · Page 8Linked to original sources
PubMed1973

Inhibition of the biosynthesis of sterols by phenyl and phenolic compounds in rat liver.

The presence of mitochondria increased the incorporation of [2-(14)C]mevalonate into sterols in a cell-free system from rat liver. Various phenyl and phenolic compounds inhibited the incorporation of mevalonate when added in vitro. p-Hydroxycinnamate, a metabolite of tyrosine, was the most powerful inhibitor among the compounds tested. Catechol, resorcinol and quinol were inhibitory at high concentrations. Organic acids lacking an aromatic ring were not inhibitory. Two hypocholesterolaemic drugs, Clofibrate (alpha-p-chlorophenoxyisobutyrate) and Clofenapate [alpha,4-(p-chlorophenyl)phenoxyisobutyrate], which are known to affect some step before the formation of mevalonate in the biosynthesis of cholesterol in vivo, showed inhibition at a step beyond the formation of mevalonate in vitro. The presence of the aromatic ring and the carboxyl group in a molecule appears to be necessary for the inhibition.

Adenosine Triphosphate↗
PubMed1973

Induction of delta-aminolaevulinate synthetase under environmental-stress conditions.

1. Exposure of rats to environmental-stress conditions of hypobaria, hypoxia and cold did not alter the activity of hepatic delta-aminolaevulinate synthetase. 2. Induction of the enzyme by diethoxycarbonyldihydrocollidine was inhibited when the rats were exposed to hypobaria before or during the treatment with the drug but not after the initial phase when the process of induction was initiated. Neither increased concentration of the drug nor the time of induction had any effect on the inhibition under hypobaria. 3. A period of 12-24h of pre-exposure to hypobaria gave the maximum inhibition, and on longer exposure the inhibitory effect was decreased. 4. The inhibition was not a permanent effect and could be substantially reversed in 12h of withdrawal to ambient pressure. 5. Inhibition of induction was found under hypobaria and hypoxia, but not on exposure to cold. This suggests a specific effect of lack of O(2) rather than a general effect of stress. 6. It appears possible that alteration of concentration of endogenous adenine nucleotides may control the process of diethoxycarbonyldihydrocollidine-mediated induction of delta-aminolaevulinate synthetase, since treatment with ATP, cyclic AMP or theophylline produced inhibition similar to that under hypobaria and hypoxia.

5-Aminolevulinate Synthetase↗
PubMed1972

Effect of hypobaric stress on enzymes of tryptophan metabolism.

1. On exposure of rats to hypobaric stress the tryptophan pyrrolase and tyrosine aminotransferase activities of the liver increased about threefold in 4h. 2. The tryptophan hydroxylase activity increased about 50% on exposure for 24h or more. 3. The increased activities reverted to the basal value on removal of the stress. 4. Treatment with cycloheximide inhibited the increase in the enzyme activities when the time of exposure was short (4h). However, the inhibitor-treated animals showed paradoxically high tyrosine aminotransferase activity on prolonged exposure (24h). 5. The pattern of haematin saturation indicated that the increase in pyrrolase activity under low pressure resembled that obtained with cortisol and not with tryptophan. 6. Repeated administration of cortisol or tryptophan did not have any effect on the activity of tryptophan hydroxylase. 7. The stress-induced increase in hydroxylase activity was not eliminated by the prior administration of 5-hydroxytryptophan to the animals.

5-Hydroxytryptophan↗
PubMed1971

Enzymic formation of p-hydroxybenzoate from p-hydroxycinnamate.

An enzyme that converts p-hydroxycinnamate into p-hydroxybenzoate was found in rat liver. It is localized in the mitochondria and requires ATP. The activity is lost when the mitochondria are stored frozen overnight. Addition of magnesium chloride, cytochrome c, GSH, coenzyme A or potassium cyanide did not have any effect on the activity. When the rats were fed with alpha-p-chlorophenoxyisobutyrate, the rate of formation of p-hydroxybenzoate increased twofold. The reaction has some similar properties to fatty acid oxidation, but appears to be different in many respects.

Adenosine Triphosphate↗
PubMed1971

Changes in the liver mitochondrial oxidation of succinate during cold-exposure.

1. Exposure of rats to low environmental temperature resulted in increased activities of several hepatic oxidative-enzyme systems. 2. Simultaneous with increase in liver ubiquinone in cold-exposed rats, the ubiquinone-dependent succinate-neotetrazolium chloride reductase activity also increased. Such an increase could also be obtained by enriching liver with ubiquinone by feeding with an exogenous source. 3. Succinate-neotetrazolium chloride reductase activity could be increased by preincubation of mitochondria with succinate and the mechanism of this activation appears to be different from that obtained on addition of ubiquinone. 4. Succinate-neotetrazolium chloride reductase activity was found to be more labile than succinate dehydrogenase on freezing and thawing and storage, and the presence of succinate gave protection against this loss in hepatic mitochondria obtained from both normal and cold-exposed animals.

Animals↗