title: Comparison of the association and orientation of gamma-glutamyltranspeptidase in lecithin vesicles and in native membranes.
abstract: gamma-Glutamyltranspeptidase purified following solubilization with Triton X-100 can associate with single-layered [14C]lecithin vesicles. Enzyme activity and radiolabeled vesicles were shown to co-migrate during Sepharose 4B chromatography and isopycnic sucrose gradient centrifugation. The enzyme-vesicle complex exhibits a density corresponding to that of a single enzyme molecule bound to a single vesicle, gamma-Glutamyltranspeptidase purified following a solubilization with papain does not bind to vesicles. In addition, papain treatment of vesicles containing the Triton-purified transpeptidase results in the release of 95% of the transpeptidase activity without release of internally trapped [3H]sucrose. The released transpeptidase is chromatographically identical to the papain-purified transpeptidase. gamma-Glutamyltranspeptidase activity associated with both native membranes and with lecithin vesicles exhibits a temperature-induced transition in its energy of activation. In contrast, the proteolytic- and detergent-solubilized forms of the enzyme exhibit a single energy of activation over the entire temperature range. These results suggest that gamma-glutamyltranspeptidase binding to vesicles is due to a papain sensitive sequence of amino acids and that the enzyme.vesicle complex closely approximates the interaction and orientation of gamma-glutamyltranspeptidase with brush border membranes.
mesh_terms: D000818:Animals; D004789:Enzyme Activation; D007668:Kidney / Q000201:enzymology; D008567:Membranes, Artificial; D008861:Microsomes / Q000201:enzymology; D008871:Microvilli / Q000201:enzymology; D010206:Papain; D010713:Phosphatidylcholines; D011092:Polyethylene Glycols; D051381:Rats; D013816:Thermodynamics; D005723:gamma-Glutamyltransferase / Q000378:metabolism
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D011092:Polyethylene Glycols; D005723:gamma-Glutamyltransferase; D010206:Papain