The Distribution of C14 in Glycogen from Deuterated Glycerol-C14 as a Measure of the Effectiveness of Triosephosphate Isomerase in Vivo

h deuterium in the stereospecific position which is removed by triosephosphate isomerase during conversion of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate. Both deuterated and nondeuterated glycerol-C/sup 14/ were administered orally to rats and the distribution of C/sup 14/ in the hexose units of liver glycogen was investigated. It was established that the presence of deuterium in the glycerol causes an increased asymmetry of the C/sup 14/ in the glucose unit. It is known that purified liver triosephosphate isomerase uses dihydroxyacetone phosphate less rapidly when it is deuterated at the position cleaved than tt does the nondeuterated dihydroxyacetone phosphate when the two species are mixed. Theoretical considerations indicate that discrimination against the deuterated species of dihydroxyacetone phosphate would be reflected in the labeling of the glyceraldehyde 3-phosphate and dihydroxyacetone phosphate and that the extent of the difference in labeling is dependent on the rate of the reversible interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phos phate. It was shown that the labeling of the glucose is consistent with predictions for such discrimination. The results provide strong evidence for the noneqnilibration of the triosephosphate pools. It is concluded that failure to achieve isotopic equilibration at the triosephosphate stage is the explanation for the unequalmore » labeling of the glucose units of liver glycogen derived from administered glycerolC/sup 14/. The present experimental approach demonstrates the use of deuterium to alter rates of reactions to evaluate the extent of equilibration of metabolic intermediates under normal physiological conditions in vivo. (auth)« less