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Biomedical subjects

M S Patel

Publications and source records attributed to M S Patel.

At least 199 records · Page 11Linked to original sources
PubMed1973

Regulation of pyruvate metabolism via pyruvate carboxylase in rat brain mitochondria.

1. The fixation of CO(2) by pyruvate carboxylase in isolated rat brain mitochondria was investigated. 2. In the presence of pyruvate, ATP, inorganic phosphate and magnesium, rat brain mitochondria fixed H(14)CO(3) (-) into tricarboxylic acid-cycle intermediates at a rate of about 250nmol/30min per mg of protein. 3. Citrate and malate were the main radioactive products with citrate containing most of the radioactivity fixed. The observed rates of H(14)CO(3) (-) fixation and citrate formation correlated with the measured activities of pyruvate carboxylase and citrate synthase in the mitochondria. 4. The carboxylation of pyruvate by the mitochondria had an apparent K(m) for pyruvate of about 0.5mm. 5. Pyruvate carboxylation was inhibited by ADP and dinitrophenol. 6. Malate, succinate, fumarate and oxaloacetate inhibited the carboxylation of pyruvate whereas glutamate stimulated it. 7. The results suggest that the metabolism of pyruvate via pyruvate carboxylase in brain mitochondria is regulated, in part, by the intramitochondrial concentrations of pyruvate, oxaloacetate and the ATP:ADP ratio.

Adenosine Diphosphate↗
PubMed1972

The effect of phenylpyruvate on pyruvate metabolism in rat brain.

1. The effect of phenylalanine and phenylpyruvate on the metabolism of pyruvate by isolated mitochondria from rat brain was investigated. 2. Phenylpyruvate inhibited the fixation of H(14)CO(3) (-) in the presence of pyruvate by intact rat brain mitochondria, whereas phenylalanine and other metabolites of this amino acid had no inhibitory effect on this process. 3. Pyruvate carboxylase activity in freeze-dried rat brain mitochondrial preparations was also inhibited only by phenylpyruvate, and a ;mixed type' inhibition was observed. 4. The K(m) for pyruvate of rat brain pyruvate carboxylase was about 0.2mm. 5. The concentration of phenylpyruvate required for a 50% inhibition of H(14)CO(3) (-) fixation by the intact mitochondria and of pyruvate carboxylase activity was dependent on the concentration of pyruvate used in the incubation medium. 6. The possible significance of inhibition of pyruvate carboxylase activity by phenylpyruvate in the brains of phenylketonuric patients is discussed.

Animals↗
PubMed1971

Pathway of carbon flow during fatty acid synthesis from lactate and pyruvate in rat adipose tissue.

The metabolism of pyruvate and lactate by rat adipose tissue was studied. Pyruvate and lactate conversion to fatty acids is strongly concentration-dependent. Lactate can be used to an appreciable extent only by adipose tissue from fasted-refed rats. A number of compounds, including glucose, pyruvate, aspartate, propionate, and butyrate, stimulated lactate conversion to fatty acids. Based on studies of incorporation of lactate-2-(3)H and lactate-2-(14)C into fatty acids it was suggested that the transhydrogenation sequence of the "citrate-malate cycle"(1) was not providing all of the NADPH required for fatty acid synthesis from lactate. An alternative pathway for NADPH formation involving the conversion of isocitrate to alpha-ketoglutarate via cytosolic isocitrate dehydrogenase was proposed. Indirect support for this proposal was provided by the rapid labeling of glutamate from lactate-2-(14)C by adipose tissue incubated in vitro, as well as the demonstration that glutamate can be readily metabolized by adipose tissue via reactions localized largely in the cytosol. Furthermore, isolated adipose tissue mitochondria convert alpha-ketoglutarate to malate, or in the presence of added pyruvate, to citrate. Glutamate itself can not be metabolized by these mitochondria, a finding in keeping with the demonstration of negligible levels of NAD-glutamate dehydrogenase activity in adipose tissue mitochondria. Pyruvate stimulated alpha-ketoglutarate and malate conversion to citrate and reduced their oxidation to CO(2). It is proposed that under conditions of excess generation of NADH malate may act as a shuttle carrying reducing equivalents across the mitochondrial membrane. Malate at low concentrations increased pyruvate conversion $$Word$$ citrate and markedly decreased the formation of CO(2) by isolated adipose tissue mitochondria. Malate also stimulated citrate and isocitrate metabolism by these mitochondria, an effect that could be blocked by 2-n-butylmalonate. This potentially important role of malate in the regulation of carbon flow during lipogenesis is underlined by the observation that 2-n-butylmalonate inhibited fatty acid synthesis from pyruvate, but not from glucose and acetate, and decreased the stimulatory effect of pyruvate on acetate conversion to fatty acids.

Acetates↗