The nature of γ-glutamyltransf erase and other hepatocyte plasma membrane enzymes in human bile

Abstract High molecular mass γ-glutamyltransferase in human bile is converted by physiological concentrations of the bile salts glycocholate and glycochenodeoxycholate to a form with a molecular mass estimated by gel chromatography to be 165000. A molecule of intermediate molecular mass estimated to be 330000 is obtained following treatment with the non-ionic detergent Triton X-100. When human bile is centrifuged at 150000 × g , between 25–73% of γ-glutamyltransferase activity is recovered in the supernatant. This proportion is increased following prior addition of bile salts to the bile. Analogous results are obtained for the high molecular mass enzymes alkaline phosphatase and leucine aminopeptidase, present in human bile, and also considered to originate from the hepatocyte plasma membrane. From these results it is suggested that these high molecular mass enzymes found in bile may, in part at least, represent artefacts following aggregation of the enzymes in aqueous media containing no bile salts.