Puromycin effect on amino acid transport: differential rates of carrier protein turnover.

In fetal rat calvaria, puromycin selectively inhibited the uptake of certain groups of amino acids. Puromycin treatment decreased the uptake of glycine, L-proline, and alpha-aminoisobutyric acid but was without effect on the active uptake of all other amino acids tested. In studies of alpha-aminoisobutyric acid uptake, puromycin decreased the maximal transport velocity by 70% but had no effect on the affinity of the transport system for the amino acid. With puromycin treatment, the fall-off in rates of alpha-aminoisobutyric acid uptake was first order with a half-life of 68 min. Insulin treatment increased this half-life to 118 min. These findings suggest that protein components of specific transport systems are degraded at varying rates after puromycin blockade of protein synthesis. Hormones that stimulate amino acid transport (e.g., insulin) may decrease the rate of degradation of these protein components.