METABOLISM OF AMINO ACIDS IN INCUBATED SLICES OF MOUSE BRAIN1

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.