METABOLISM OF GLYCINE-l-C’* AND GLYCINE-2-C’* IN RAT BRAIN HOMOGENATES* BY LEMUEL

In 1932, Quastel and Wheatley (1) measured oxygen consumption in chopped brain tissue to which various metabolites had been added. Glutamic acid was oxidized at a relatively slow rate. According to Krebs (2), who repeated and extended these studies, L-glutamic acid was the only amino acid which was capable of maintaining the respiration of slices of brain or retina. This observation was confirmed by Weil-Malherbe (3). Krebs (4) also indicated that the analysis of ammonia liberated from the amino acids was not adequate, since in some experiments no ammonia but amide nitrogen was found when glutamic acid had been added to the brain slices. Later, Edlbacher and Wiss (5) measured the ammonia produced when amino acids were incubated with brain homogenates because they observed that in some instances addition of the amino acid did not cause an increased oxygen consumption. According to these investigators, other amino acids besides glutamic acid (except glycine and histidine) were oxidatively deaminated by brain. In comparison with the reactivity of glutamic acid, however, that of the other amino acids (particularly of the L forms) was small. The following study was undertaken to test the validity of these conclusions with the aid of l-C’*and 2-Cl*-labeled glycine.