Gamma-glutamyltranspeptidase isoenzyme forms and lipoproteins in normal and pathological sera

The molecular nature of serum (from normal subjects and from patients affected by various hepatobiliary diseases) gamma-glutamyltranspeptidase (GGT) isoenzymes has been studied by selective lipoprotein precipitation. Some fractions co-precipitate with LDL + VLDL (pre-beta-, beta-, beta/gamma-, gamma-, and dep-GGT fractions) or with HDL (partial precipitation of alpha 1-GGT in cirrhosis). Alpha 1-GGT + alpha 2-GGT in normal subjects, and Alb-GGT did not precipitate with either of the precipitation treatments. Total GGT and its isoenzymes were stable at 4 degrees C and at -20 degrees C for at least 20 days, with the exception of Alb-GGT which at -20 degrees C decreased by 20%. The percentage of GGT associated with LDL + VLDL appeared to be a possible marker to discriminate liver tumors from cirrhosis. A cut-off value of 20 U/L of this marker yielded a diagnostic sensitivity of 87% and a diagnostic specificity of 85%.