Characterization of human serum gamma-glutamyltranspeptidase

The contribution of proteolysis to leakage of gamma-glutamyltranspeptidase from the liver into the serum was examined by comparing the properties of human serum gamma-glutamyltranspeptidase with those of partially purified enzyme preparations solubilized from human liver with Triton X-100 and with papain. The Triton-solubilized enzyme was hydrophobic, whereas the papain-solubilized enzyme was hydrophilic. Serum gamma-glutamyltranspeptidase was found to be hydrophilic, since it could be extracted without addition of detergent after acetone treatment to remove bound cholate. The affinity of serum-gamma-glutamyltranspeptidase to concanavalin A-Sepharose was compared with those of the Triton-solubilized and papain-solubilized enzymes. All three enzymes were adsorbed to concanavalin A-Sepharose in 50 mmol/l imidazole buffer, pH 7.2. The serum enzyme and papain-solubilized enzyme were eluted with 100 mmol/l alpha-methylmannoside in 50 mmol/l imidazole buffer containing 1% Triton X-100. The molecular weights of the Triton-solubilized, papain-solubilized and serum-gamma-glutamyltranspeptidases were estimated as 98 000 +/- 2000, 90 000 +/- 2000 and 90 000 +/- 2000, respectively, by electrophoresis. These results show chemical similarities between the serum-gamma-glutamyltranspeptidase and papain-solubilized gamma-glutamyltranspeptidase.