Biosynthesis of rat renal gamma-glutamyl transpeptidase. Evidence for a common precursor of the two subunits.
Rat kidney gamma-glutamyl transpeptidase is an amphipathic heterodimer, anchored to the lumenal surface of brush-border membranes via the NH2-terminal portion of its heavy subunit. The Mr values of the two subunits of detergent-solubilized enzyme are approximately 51,000 (heavy) and 22,000 (light), respectively. Biosynthesis of transpeptidase was studied in renal slices incubated with L-[35S]methionine. Transpeptidase-related proteins were isolated by immunoprecipitation with anti-transpeptidase antibodies. The major species seen after relatively short pulse times is a 78,000-dalton protein. Immunological characterization, kinetic, and pulse-chase studies indicate that the Mr = 78,000 species is the precursor of the two subunits of the enzyme. Like the dimeric enzyme, the Mr = 78,000 species contains both the core and the peripheral sugar, fucose, on its oligosaccharide moieties. Since, only the labeled dimeric enzyme appears in the brush-border membranes, conversion of the Mr = 78,000 species to the two subunits presumably occurs after its arrival at the Golgi but before its transport to the brush-border surface.
D000818:Animals; D007672:Kidney Cortex / Q000201:enzymology*; D007700:Kinetics; D046911:Macromolecular Substances; D008297:Male; D008715:Methionine; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D013462:Sulfur Radioisotopes; D005723:gamma-Glutamyltransferase / Q000096:biosynthesis*
D046911:Macromolecular Substances; D013462:Sulfur Radioisotopes; D008715:Methionine; D005723:gamma-Glutamyltransferase