Processing of the propeptide form of rat renal γ-glutamyltranspeptidase

The biosynthesis of rat renal γ-glutamyltranspeptidase (EC 2.3.2.2) was studied by sodium dodecyl sulfate gel electrophoresis and fluorography of specific immunoprecipitates obtained at varying times' postinjection with [ 35S]methionine. At 20 min postinjection 3 endo-β- N-acetylglucosaminidase H-sensitive bands were observed representing the propeptide ( M r 75 000) large subunit ( M r 49 500) and small subunit ( M r 29 000) of transpeptidase. The alterations in M r are consistent with removal of 6 N-linked coreoligosaccharides from the propeptide; 4 from the large subunit and 2 from the small subunit. All 3 bands became more diffuse and less endoglycosidase H-sensitive by 40 min and completely resistant by 60 min postinjection. At 20 h postinjection no propeptide remained. Thus, the primary propeptide cleavage reaction occurs prior to the loss of endoglycosidase H sensitivity while about 30% of the propeptide is processed along with the heterodimer and cleaved at a later time.