Variations in gamma-glutamyl transpeptidase glycosylation and kinetic parameters in cultured liver cells.
In rat hepatocytes; the tumorigenic rat liver cell line ARL-16; and the human hepatoma line, Hep G2, 50% of the total gamma-glutamyl transpeptidase (GGT) activity was bound by a Concanavalin-A Sepharose 4B column, calling for alpha-methylmannoside elution (Peak I). Non-binding GGT was distributed between a rapidly eluting Peak II and a slightly retained Peak III. The Km for gamma-glutamyl-p-nitroanalide for either hydrolysis or transpeptidation, or glutathione (GSH) transpeptidation did not vary with peak number or cell type. The GSH hydrolysis Km was essentially constant in Peak I and II GGT. Peak III GGT exhibited a lower Km for GSH hydrolysis with Hep G2 Peak III GGT being the lowest. Peak III GGT increased to 50% of the GGT activity in Hep G2 cells cultured with GSH as the sole cysteine source.
Meredith
M J
MJ
Department of Biochemistry, School of Dentistry, Oregon Health Sciences University, Portland 97201.
D000818:Animals; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D002478:Cells, Cultured; D003208:Concanavalin A / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008113:Liver Neoplasms / Q000201:enzymology*; D051381:Rats; D014407:Tumor Cells, Cultured; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D003208:Concanavalin A; D005723:gamma-Glutamyltransferase; D005978:Glutathione; D003545:Cysteine