Characteristics of gamma-glutamyltranspeptidase in cultured skin fibroblasts from normals and cystinotics.

The characteristics of a fluorimetric method for assay of gamma-glutamyltranspeptidase (EC 2.3.2.2) in cultured human skin fibroblasts from normal donors and cystinotic patients using gamma-glutamyl-7-amino-4-coumarin as substrate are described. It is possible with this method to measure enzymatic activity in sonicates of cells with as little as 0.029 mmol/l L-cystine as acceptor-substrate with only 0.20 mg of cellular protein after 30--60 min of incubation. The properties of the enzyme in cells from patients with cystine storage disease show elevated gamma-glutamyltranspeptidase under various incubation conditions.