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.

In vivo 14C isotopic evaluation of amino acid oxidative catabolism in the growing chick. I. Fast respiratory 14CO2 and acetyl-CoA renewal.

A single dose of [1-14C] or [U-14C]glycine or L-[1-14C] or [U-14C]valine was injected intraperitoneally into 1- and 3-week-old chicks. Continuous automatic determination of respiratory 14CO2 and determination of 14C in excreta and uric acid were carried out for 8 h. Computer-aided analysis of the kinetics of respiratory 14CO2 demonstrated two exponentially decreasing components, 'fast 14CO2' and slow 14CO2'.