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Serum gamma-glutamyltransferase (EC 2.3.2.2) showed microheterogeneity on electrofocusing, owing to variations in sialic acid content. We investigated the isoform patterns of papain-treated serum samples on agarose gels containing nonionic detergent and ampholytes in the low pH range. Serum from cases of cholestasis show seven bands with gamma-glutamyltransferase activity. These same bands were also found in liver tissue similarly treated, and they had pl 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 pl of 5.9. Increased gamma-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 during several weeks of abstinence was accompanied by a gradual decrease in gamma-glutamyltransferase sialyation and the appearance of more cathodal fractions.
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Lilja et al. (1983) studied this question.
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