Evidence for the presence of a precursor form to gamma-glutamyl transpeptidase in cultured yolk sac tumor cells.

The biosynthesis of gamma-glutamyl transpeptidase was studied in a yolk sac tumor cell line. Cell suspensions were labeled with [14C]leucine; immunoprecipitates were obtained with anti-gamma-glutamyl transpeptidase antibody and analyzed on SDS-polyacrylamide gel electrophoresis++. A radioactive 80 000 dalton peak and peaks identical to heavy and light subunits were detected in the immunoprecipitates from the extract which was labeled for 15 min. After 45 min labeling, the 80 000 dalton species disappeared, although the two subunits were still observed. Tunicamycin-pretreated cells were labeled with [3H]glucosamine and [14C]leucine for 3.5 h. The 80 000 dalton species was glycosylated, and accumulated to a great degree compared to non-treated cells.