Growth in Mice Fed Diets Rendered Deficient in Cystine, but Not in Methionine

Abstract

Mice fed 14.7% of casein and 0.3% of cystine in diets complete in other factors grew slightly better than mice fed 18 or 32% of casein. When a hydrolysate of casein, deficient in cystine but not in methionine, was incorporated at a level of 14.8% in a diet along with 0.2% of tryptophane, it supported growth less well than when it was further supplemented with cystine or methionine, or both. Growth on the unsupplemented diet and its acceleration to the same extent by the addition of either cystine or methionine both suggest that the mouse is able to synthesize cystine when methionine is provided.