Hydrogen isotope effects in the in vivo utilization of formate

Abstract The hydrogen isotope effects in the utilization of formate in the rat were investigated with formate labeled intermolecularly with deuterium, tritium, and C 14 . Following the administration of this triply labeled formate, the isotope ratios of the formate excreted in the urine and of the methyl groups of tissue choline and creatine were determined and compared with the same ratios in the injected formate. The results indicate extensive selection among the hydrogen isotopes during the metabolism of formate. Intramolecular multiple labeling is suggested as a means of allowing less equivocal interpretations of isotope ratios in studies of the metabolism of C-H units.