gamma-Glutamyl transpeptidase of rat liver and hepatoma tissues: an enzyme immunoassay and immunostaining studies.

A sensitive enzyme immunoassay method for rat gamma-glutamyl transpeptidase was developed that was able to quantitate between 5 to 500 ng of the enzyme. The enzyme contents of fetal liver, adult liver, hyperplastic nodules, and various tissues including hepatoma were determined. Normal rat liver contained very little enzyme, while fetal liver and hepatoma tissue contained high levels. The gamma-glutamyl transpeptidase content of the liver was assayed during the process of 3'-methyl 4-dimethyl-aminoazobenzene-induced hepatocarcinogenesis. The content was increased at an early stage, then decreased, and again increased at the stage when hepatoma developed. The change of the enzyme content determined by an enzyme immunoassay was highly consistent with that determined by enzymatic assay. This indicates that the increased activity of the enzyme as previously reported was accompanied by an increased immunoreactive enzyme protein. Immunohistochemical studies on the hyperplastic nodule revealed the presence of gamma-glutamyl transpeptidase in the hepatocyte membrane.