Immunological characterization of gamma-glutamyltransferases in human serum

The immunological properties of gamma-glutamyltransferases (gamma-GTs) from human serum, liver and tonsil were studied by using a monospecific antibody to human kidney gamma-GT for the purpose of elucidating their isozymic relationships. gamma-GTs partially purified from liver and tonsil were indistinguishable in this respect from kidney gamma-GT. gamma-GT in sera from patients with hepato-biliary diseases, on the other hand, was heterogeneous in molecular size as revealed by sucrose density gradient centrifugation 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 gamma-GT was reduced and the enzyme now reacted with the antibody as strongly as kidney gamma-GT. gamma-GT from bromelain-treated sera also exhibited a single immunoprecipitin line smoothly fusible with that from kidney gamma-GT; the enzyme-antibody complex still exhibited gamma-GT activity. The major form of gamma-GT partially purified from papain-treated sera, even though indistinguishable from kidney gamma-GT immunologically and in molecular size, exhibited a mobility on polyacrylamide gel electrophoresis which was higher than that of kidney gamma-GT but similar to that of liver gamma-GT. It is suggested that gamma-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 gamma-GT.