Measurement of human serum immunoreactive gamma-glutamyl transpeptidase in patients with malignant tumors using enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay for human immunoreactive gamma-glutamyl transpeptidase (gamma-GTP) was developed. This assay was found to be simple, reproducible, and sensitive to 10 ng of the enzyme. Serum immunoreactive gamma-GTP content was significantly elevated in patients with various malignant tumors including liver cell cancer, lung cancer, gastric cancer, esophageal cancer, and colorectal cancer. On the other hand, in sera of patients with nonneoplastic diseases, the immunoreactive gamma-GTP content was not significantly elevated. No correlation was found between the serum levels of gamma-GTP determined by enzymatic assay and enzyme-linked immunosorbent assay, which indicates that, due to the presence of endogenous inhibitors and/or activators in sera, the enzyme activity may not reflect the true amount of enzyme protein. The measurement of immunoreactive gamma-GTP protein in sera appears to be useful for the detection and monitoring of certain malignant tumors.