gamma-Glutamyltranspeptidase: a tumour cell marker with a pharmacological function.

The distribution of gamma-glutamyltranspeptidase activity (gamma GT) in adult, foetal, and neoplastic tissues in rats and humans is reviewed. The normal adult kidney, pancreas, and jejunum are high in this activity. Around the time of birth, gamma GT activity increases transiently in the liver, colon, and skin; many tumours of these organs often have elevated activity as well. Although this activity in tumour tissue may reflect a general expression of onco-foetal genes, subpopulations of cells having abnormally high gamma GT may have a selective growth advantage over their normal counterparts. We explore this latter possibility by considering the pharmacological function this enzyme may play. gamma GT may facilitate the detoxification of electrophiles by glutathione conjugation, so that cells can survive in an otherwise toxic environment. This growth advantage may be particularly important to the development of liver tumours in rats during chemical carcinogenesis.