METABOLISM OF D-[1-H-3]GLUCOSE, D-[2-H-3]GLUCOSE, D-[5-H-3]GLUCOSE, D-[6-H-3]GLUCOSE AND D-[U-C-14]GLUCOSE BY RAT AND HUMAN ERYTHROCYTES INCUBATED IN THE PRESENCE OF H2O OR D2O

The present study investigates whether heavy water affects the efficiency of (HOH)-H-3 production from D-[1-H-3]glucose, D-[2-H-3]glucose, D-[5-H-3]glucose and D-[6-H-3]glucose relative to the total generation of tritiated metabolites produced by either rat or human erythrocytes. The relative (HOH)-H-3 yield was close to 95% with D-[5-H-3]glucose, 72% with D-[2-H-3]glucose, 22-32% with D-[1-H-3]glucose, and only 12% with D-[6-H-3]glucose. In the latter case, the comparison of the specific radioactivity of intracellular and extracellular acidic metabolites, expressed relative to that of C-14-labelled metabolites produced from D-[U-C-14]glucose, indicated that the generation of (HOH)-H-3 from D-[6-H-3]glucose occurs at distal metabolic steps, such as the partial reversion of the pyruvate kinase reaction or the interconversion of pyruvate and L-alanine in the reaction catalysed by glutamate-pyruvate transaminase. As a rule, the substitution of H2O by D2O only caused minor to negligible changes in the relative (HOH)-H-3 yield. This implies that the unexpectedly high deuteration of C-13-labelled D-glucose metabolites recently documented in erythrocytes exposed to D2O cannot be attributed to any major interference of heavy water with factors regulating both the deuteration and detritiation efficiency, such as the enzyme-to-enzyme tunnelling of specific glycolytic intermediates.