The cause(s) for decreased reduced glutathione (GSH) content of human senile cataracts were investigated by determination of three enzymes of GSH metabolism: GSH S-transferase, GSH peroxidase and GSH reductase. There are significant decreases in activities of GSH S-transferase of early cataracts (––76%) and of dark advanced cataracts (––73%) as compared to clear age-matched lenses. However, the activities of GSH peroxidase were only slightly decreased in cataracts as compared to clear age-matched lenses. The decrease in enzymes of GSH metabolism does not account for increased GSH degradation. Thus decreased GSH synthesis and leak out from cataractous lenses may account for the GSH loss in cataracts.
Acute effects of intraperitoneal administration of ammonium chloride (200 mg/kg) on Na(+),K(+)-ATPase and amino acid content of the glutamate family (glutamate, aspartate, alanine, glutamine, and GABA), as well as the enzymes involved in the metabolism of these amino acids, have been studied in the different regions of brain and liver in mice. A significant increase in the activity of Na(+),K(+)-ATPase was observed in the cerebellum, cerebral cortex, and brain stem. A similar increase in the activity of glutamate dehydrogenase was observed in the brain stem, while a moderate increase in the activity of this enzyme was observed in the cerebral cortex and liver in the mice treated with ammonium chloride. In all three regions of brain, a 50% decrease was observed in the activity of alanine aminotransferase, while the activity of aspartate aminotransferase significantly rose in the brain stem. The activity of glutamine synthetase did not change much in the three regions of brain, and a significant fall was registered in the liver. The activity of tyrosine aminotransferase showed a rise in the cerebellum, brain stem, and in liver. Not much change was observed in the protein content in either brain or liver, whereas there was a 1.5-fold increase in the total RNA content in the liver of the animals treated with ammonium chloride. Under the experimental conditions, there was an increase only in the content of glutamine, of all the amino acids tested, in the cerebral cortex and liver. Similar results were obtained with homogenates of tissues enriched with ammonium chloride (in vitro) for the enzyme systems studied. These results are discussed, and the probable metabolic and functional significance of ammonia in brain is indicated.
Abstract— Slices of mouse brain were incubated with [U‐14C]alanine, valine, leucine, phenylalanine, proline, histidine, lysine, arginine or aspartic acid, and the extent of metabolism was estimated by analyses utilizing paper chromatography of the tissue extracts and with an amino acid analyser. The metabolism of Ala and Asp was high; of Leu and Pro, moderate; and of Lys, Arg and Phe, low; the metabolism of Val and His was not significant. The time‐course of metabolism in most cases showed varying rates, indicating heterogeneous metabolic compartments for the amino acids. Production of CO2 was high from Asp, moderate from Ala, and low from Leu; the other amino acids were not oxidized to CO2 to any significant extent. A large portion of the metabolized label was trapped in the form of Glu or Asp. Metabolism increased with increasing concentration of amino acid to some extent and was largely inhibited by omission of glucose, by anaerobic conditions, or by cyanide. Although these conditions also inhibit uptake, the time‐course and extent of inhibition uptake and metabolism were different. With Asp, Ala and Phe, metabolism was lowest in slices from pons‐medulla; the brain area exhibiting the highest metabolism differed for each amino acid. The metabolism of Asp was lower in brain samples from newborn than in those from adults; the metabolism of Leu was higher in slices from newborn brain. The results indicate that the majority of the amino acids can be metabolized in brain tissue and that the metabolic rates are influenced by a number of factors, among them the level of amino acids and the level of available energy.
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