Purification and Properties of Bovine Liver γ-Glutamyltransferase

Abstract

γ-Glutamyltransferase [EC 2. 3. 2. 2] (γ-GTP) was purified to a homogeneous state from bovine liver. It had an apparent molecular weight of about 110, 000, as judged by polyacrylamide gel electrophoresis, and consisted of two non-identical glycopeptides with molecular weights of 68, 000 and 27, 000. The amino acid composition of the bovine liver enzyme was similar to those of other γ-GTPs. The enzyme contained large amounts of neutral sugars, amino sugars and sialic acid, although the sialic acid content varied in different preparations. The Michaelis constant of the enzyme was estimated to be 0.8mM for γ-L-glutamyl-p-nitroanilide in the presence of glycylglycine and 1.25mM in the absence of glycylglycine. Glutathione competitively inhibited the release of p-nitroaniline from γ-L-glutamyl-p-nitroanilide with a K₁ value of 0.3mM. The specific activities of the enzyme for γ-L-glutamyl-p-nitroanilide in the presence of glycylglycine (pH 8.6) and for gluta-thione, a natural substrate (pH 7.4), were comparable to those reported for γ-GTPs from other mammalian sources. The bovine liver enzyme showed the same γ-glutamyl group acceptor specificity as other γ-GTPs from normal mammalian tissues. The phosphate-independent glutaminase activity of the enzyme was much lower than that of the rat kidney enzyme both in the presence and absence of maleate.