Isolation of γ-glutamyltransferase from human liver, and comparison with the enzyme from human kidney

Abstract

The authors isolated γ-glutamyltransferase [(γ-glutamyl)-peptide: amino acid γ-glutamyltransferase, EC 2.3.2.2] from human liver and compared some of its properties with the same enzyme prepared from human kidney. The enzymes from these two sources are very similar with respect to initial velocity kinetic constants, pH optima of the transpeptidation and autotransfer reactions, heat stability, competitvie inhibition by glutathione of the colorimetric assay in which γ-glutamyl-4-nitroanilide is substrate, stability of catalytic activity to trypsinization, and relative rates of transfer of the γ-glutamyl moiety from γ-glutamyl-4-nitroanilide and L-[glycine-2-3H] glutathione to some amino acids and small peptides. The kidney enzyme is inhibited more by the γ-glutamyl acceptor substrate, glycylglycine, as reflected in a sevenfold lower value for the inhibition constant K(i)(A). Major differences were observed in the lectin-binding properties of liver γ-glutamyltransferase compared to the kidney enzyme. Lectin-binding property differences are retained for the trypsinized form of the liver and kidney enzymes, although the degree of precipitation was less for certain lectins as compared to the untreated enzyme. Lectin-binding properties were reversed by carbohydrates specific for each lectin. The authors adapted the histochemical staining technique of Rutenberg et al. [J. Histochem. Cytochem. 17, 517 (1969)] to the detection of γ-glutamyltransferase activity in acrylamide gels; diffusion artifacts are minimized and the color produced is stable for several days. Untreated and trypsinized forms of the liver enzyme both migrated faster in acrylamide gels (as single bands) than did the corresponding forms of the kidney enzyme.