The Effects of Tryptophan Deficiency upon Enzyme Activity in the Rat*

Recently it has been observed that liver enzyme activity may be markedly affected by dietary conditions. Seifter et al. (1) have demonstrated that during complete dietary protein deprivation loss of arginase and n-amino acid oxidase from rat liver occurs more rapidly than loss of general liver protein. We (2) have observed that the level of xanthine oxidase activity in rat liver may be altered by subtle protein changes in the ration. Adult rats fed a diet completely adequate for maintenance showed a decreased liver xanthine oxidase content which was returned to normal by addition of methionine to the ration. It appeared that liver xanthine oxidase activity was a fairly sensitive index of dietary amino acid availability. In a previous study of the effects of methionine deficiency upon liver enzyme activity, it was noted’ that complete deprivation of dietary methionine reduced liver xanthine oxidase activity almost completely, decreased succinic oxidase activity somewhat, and had no demonstrable effect upon liver endogenous respiration. In the present paper the study of the effects of amino acid deficiencies upon liver enzyme activity has been extended to tryptophan. By studying the relation of individual amino acid deficiencies to liver enzyme activity, it is hoped that some light will be thrown upon amino acid, enzyme, and animal protein metabolism in general. The enzyme systems we have chosen for study in this work are liver xanthine oxidase, succinic oxidase, cathepsin, endogenous respiration, and fatty acid oxidase. Since xanthine oxidase activity has been observed to be very sensitive to dietary protein changes, this enzyme was one of those chosen for the present study. The possibility that increased breakdown of body proteins during a tryptophan deficiency might involve a greater need for liver protease activity led us to study liver catheptic activity as a