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 [ 35 S]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.