STUDIES ON THE STRUCTURE OF GAMMA-GLUTAMYL-TRANSPEPTIDASE .1. CORRELATION BETWEEN SIALYLATION AND ISOZYMIC FORMS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 87  (4) , 1243-1248
Abstract
Papain solubilized .gamma.-glutamyltranspeptidase was purified by DEAE-cellulose column chromatography. Four fractions were obtained as single proteins, each with a single isoelectric point, and 5th and 6th fractions were obtained as mixtures of several components. The molecular weights of the subunits of each form and their amino acid compositions and carboxyl-terminals were identical. The isoelectric points of the 4 purified enzymes and the main bands of the 5th fraction were pH 8.3, 8.0, 7.5, 6.7 and 6.0, respectively. The 6th fraction gave 5 bands with isoelectric points of pH 5.6, 5.3, 5.1, 4.6 and 4.4. An asialo-form of the enzyme, obtained by treatment with neuraminidase, had an isoelectric point of pH 8.6. A linear relationship was found between the isoelectric points of the enzymes and their contents of sialic acid, indicating that the heterogeneity of papain-solubilized .gamma.-glutamyltranspeptidase is mostly due to differences in the extents of sialylation of the enzymes. Distribution of the activity in rat kidney was 29% in a poorly sialylated fraction (isoelectric point (Ip) 8.3 to 6.7), 24% in a moderately sialylated fraction (Ip 6.6 to 6.0) and 45% in a highly sialylated fraction (Ip 5.6 to 4.4).

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