GENERATION OF C-3-DEUTERATED AND C-2-DEUTERATED L-LACTIC ACID BY HUMAN ERYTHROCYTES EXPOSED TO D-[1-C-13]GLUCOSE, D-[2-C-13]GLUCOSE AND D-[6-C-13]GLUCOSE IN THE PRESENCE OF D2O

1. The generation of C-2- and C-3-deuterated L-lactate was monitored by C-13 NMR in human erythrocytes exposed to D-[1-C-13]glucose, D-[2-C-13]glucose or D-[6-C-13]glucose and incubated in a medium prepared in D2O. 2. The results suggested that the deuteration of the C-1 of D-fructose 6-phosphate in the phosphoglucoisomerase reaction, the deuteration of the C-1 of D-glyceraldehyde-3-phosphate in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase and the deuteration of the C(?)3 of pyruvate in the reaction catalyzed by pyruvate kinase were all lower than expected from equilibration with D2O. 3. Moreover, about 40% of the molecules of pyruvate generated by glycolysis apparently underwent deuteration on their C-3 during interconversion of the 2-keto acid and L-alanine in the reaction catalyzed by glutamate-pyruvate transaminase. 4. The occurrence of the latter process was also documented in cells exposed to exogenous [3-C-13]pyruvate. 5. This methodological approach is proposed to provide a new tool to assess in intact cells the extent of back-and-forth interconversion of selected metabolic intermediates.