Association of gamma-glutamyltransferase with plasma lipoprotein and lipid-protein complex in cholestasis.

Distribution of plasma gamma-glutamyltransferase (GGT) activity among lipoproteins was studied by ultracentrifugation and polyacrylamide gradient gel electrophoresis of plasma from 2 normal controls, 7 patients with intrahepatic cholestasis, and 5 patients with biliary obstruction. Half the total plasma activity was associated with lipoproteins, and more than 90 per cent of the residue activity with macromolecular lipid-protein complex. Healthy subjects had the highest GGT activity in HDL, intermediate activity in LDL, and the lowest in VLDL. In cholestasis, GGT activity increased mainly by the following two mechanisms: 1) the appearance of cholestatic lipoproteins carrying GGT, such as lipoprotein X or Slow-Migrating HDL, or increase in concentration of lipid-protein complex with GGT activity and 2) increase in GGT activity per unit weight of HDL.