The identification of two subcellular sites for cleavage of gamma-glutamyltranspeptidase propeptide.

In order to determine the subcellular site(s) of rat renal gamma-glutamyltranspeptidase propeptide cleavage labeled immunoprecipitates were obtained from preparations of either intracellular membranes or brush border membrane vesicles. Heterodimer accounts for 25% of the label associated with transpeptidase in intracellular membranes from 5 to 40 min postinjection of [35S]methionine, consistent with a cotranslational cleavage of propeptide in the endoplasmic reticulum. Labeled propeptide and heterodimer appear in the brush border membrane fraction between 20-30 min postinjection and accumulate for 1 h and 4h, respectively. Subsequently, the propeptide disappears with a half-life of 1 h while the heterodimer is relatively stable. These results confirm our previous proposal for two distinct subcellular sites for transpeptidase propeptide cleavage (Capraro, M.A. and Hughey, R.P. (1983) FEBS Lett. 157, 139-143).