Normal amino acid uptake by cultured human fibroblasts does not require gamma-glutamyl transpeptidase.

The uptake kinetics for four amino acids (cystine, glutamine, methionine, and alanine) which are among the best gamma-glutamyl acceptors have been determined for normal human fibroblasts and for a cell line containing undetectable quantities (< 0.5% normal mean) of gamma-glutamyl transpeptidase activity. Apparent Km and V(max) for uptake for each of the four amino acids were normal in the mutant fibroblasts.