Immunological Characterization of γ-Glutamyltransferases in Human Serum1

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Abstract
The immunological properties of γ-glutamyltransferases (γ-GTs) from human serum, liver and tonsil were studied by using a monospecific antibody to human kidney γ-GT for the purpose of elucidating their isozymic relationships. γ-GTs partially purified from liver and tonsil were indistinguishable in this respect from kidney γ-GT. γ-GT in sera from patients with hepato-biliary diseases, on the other hand, was heterogeneous in molecular size as revealed by sucrose density gradient centrifu-gation and Sephadex G-150 gel filtration, and was inhibited and precipitated by the above antibody relatively poorly as compared with the kidney enzyme. When these sera were treated with bromelain, however, the molecular size of γ-GT was reduced and the enzyme now reacted with the antibody as strongly as kidney γ-GT. γ-GT from bromelain-treated sera also exhibited a single immunoprecipitin line smoothly fusible with that from kidney γ-GT; the enzyme-antibody complex still exhibited γ-GT activity. The major form of γ-GT partially purified from papain-treated sera, even though indistinguishable from kidney γ-GT immunologically and in molecular size, exhibited a mobility on polyacrylamide gel electrophoresis which was higher than that of kidney γ-GT but similar to that of liver γ-GT. It is suggested that γ-GT in human sera is heterogeneous in molecular size and electric charge but is composed of common peptide chains, probably identical to those of kidney γ-GT.