In vivo 14C isotopic evaluation of amino acid oxidative catabolism in the growing chick. II. Slow respiratory 14CO2 and protein renewal.

Analysis of the respiratory 14CO2 of growing chicks injected intraperitoneally with [1-14C] or [U-14C]glycine or valine has shown the presence of a delayed 'slow 14CO2' exponential component. The half-lives, about 3 h, are independent of the nature of the amino acid and of the age (1-3 weeks) of the animal. As supported by investigations in cycloheximide-treated chicks of the oxidative catabolism of glycine, valine and acetate, slow 14CO2 is significantly associated with the degradation of short-lived proteins.