APPORTIONING TRYPTOPHAN REQUIREMENTS FOR MAINTENANCE VERSUS GROWTH OFRATS

Purified diets containing six levels of tryptophan were fed to growing rats to determine tryptophan requirements for growth and for maintena nce. A mathematical model was employed to subdivide the tryptophan nee d for maintenance from its requirement for growth. Based on the model relating weight gain to tryptophan intake, the tryptophan need for gro wth was 2.48 mg/g weight gain and the daily tryptophan need for mainte nance (mg) was 0.066 times metabolic body size (W-g(.75)). Based on a the model relating nitrogen gain to tryptophan intake, the tryptophan need for growth was 0.11 mg/mg nitrogen retention and the daily trypto phan need for maintenance was 0.078 times metabolic body size (W-g(.75 )). Previous tryptophan requirements for growth and for maintenance co rresponded very closely with these estimates. As a percentage of depos ited protein, according to these equations, tryptophan was calculated to be 1.7%; the reported tryptophan content of rat muscle crude protei n is 1.8%.