Synthesis of Protein and Amino Acids in Mice with the Aid of Deuterium

Abstract

Schoenheimer and Rittenberg 1 have proposed that if non-labile deuterium is found in the molecule of a fatty acid isolated from tissues of mice which were receiving heavy water, this finding is then indicative of the synthesis of the fatty acid in the animal body. In connection with the study of the synthesis of protein and amino acids in animals, we were interested to ascertain whether or not a similar criterion, as used by Schoenheimer and Rittenberg, is applicable to protein and amino acid synthesis. Barbour, et al., 2 on the assumption that one hour after a single injection of D₂O into mice a maximum of exchangeable deuterium will be fixed in the tissue, conclude that inasmuch as “mice drinking 15% D₂O for 2 months have 3 times the concentration of deuterium (relative to body water deuterium) in the tissue as mice receiving a single injection of D₂O,'the difference in the deuterium content of the tissue indicates the fixation of deuterium in tissue in stable form. It occurred to us that the isolation of tissue protein and of amino acids derived therefrom and the analysis of the isolated products from which all deuterium in labile position has been removed would constitute more direct evidence for the fixation of deuterium in the protein in stable form than the one offered by Barbour. 2 Twenty adult and 20 growing mice were used in a preliminary study. The animals were kept, each group separately, in metabolism cages and 2% D₂O and food consisting of 70 parts of oats, 15 of yeast powder and 15 of “Klim'milk powder were allowed ad libitum. A record of food and water consumption of the young mice was taken daily.