Abstract
The present study investigates whether heavy water affects the efficiency of 3HOH production from D-[1- 3H]glucose, D-[2- 3H]glucose, D-[5- 3H]glucose and D-[6- 3H]glucose relative to the total generation of tritiated metabolites produced by either rat or human erythrocytes. The relative 3HOH yield was close to 95% with D-[5- 3H]glucose, 72% with D-[2- 3H]glucose, 22–32% with D-[1- 3H]glucose, and only 12% with D-[6- 3H]glucose. In the latter case, the comparison of the specific radioactivity of intracellular and extracellular acidic metabolites, expressed relative to that of 14C-labelled metabolites produced from D-[U- 14C]glucose, indicated that the generation of 3HOH from D-[6- 3H]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 H 2O by D 2O only caused minor to negligible changes in the relative 3HOH yield. This implies that the unexpectedly high deuteration of 13C-labelled D-glucose metabolites recently documented in erythrocytes exposed to D 2O 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.
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