Ribonucleic acid metabolism in the liver after administration of individual amino acids

Abstract

The uptake of P32 by liver ribonucleic acid was studied after administration of certain proteins, amino acid mixtures and individual amino acids. Feeding with zein resulted in the same increase in P32 uptake as did the feeding with casein. Addition of tryptophan and lysine to zein did not alter the magnitude of the response. Of 18 amino acids fed singly in large doses, glycine, methionine and leucine each caused a significant increment in uptake of P32. The responses after feeding methionine and leucine were proportional to the dose administered, whereas the response to glycine occurred only after a threshold dose had been reached. Experiments with a mixture of amino acids in the proportions found in zein confirmed that its high leucine content accounts for a large part of its action on the metabolism of ribonucleic acid. The protein content of the liver is increased by the administration of leucine, and it is concluded that the changes in metabolism of ribonucleic acid after the feeding of glycine, methionine and leucine are secondary to an increased rate of synthesis of liver protein.