Evaluation of Serum y-Glutamyltransferase by Electrofocusing, and Variations in lsoform Patterns

Serum y-glutamyltransferase (EC 2.3.2.2) showed microheterogeneity on electrofocusing, owing to variations in sialic acid content. We investigated the isoform patterns of papaintreated serum samples on agarose gels containing nonionic detergent and ampholytes in the low pH range. Serum from cases of cholestasis show seven bands with y-glutamyltransferase activity. These same bands were also found in liver tissue similarly treated, and they had p1 values ranging from 3.8 to 4.2. Papain-treated sera that also had been neuraminidase digested showed only a single band, still enzymatically active and with a p1of 5.9. Increased y-glutamyltransferase in serum as a result of alcohol abuse was combined with a abnormally high degree of sialylation of the enzyme, giving more anodal isoforms. The decline in the concentration of this enzyme dunng several weeks of abstinence was accompanied by a gradual decrease in y.glutamyltransferase sialylation and the appearance of more cathodal fractions.