γ-Glutamyl transpeptidase: What does the organization and expression of a multipromoter gene tell us about its functions?

γ-Glutamyl transpeptidase is a key enzyme in glutathione (GSH) salvage, metabolism of endogenous mediators such as leukotrienes and prostaglandins, detoxification of xenobiotics including environmentally important compounds and carcinogens, and cellular processes dependent on the oxidation/reduction of glutathione. The enzyme is widely distributed, and these functions often occur in separate tissues and in response to different stimuli. Evidence indicates that γ-glutamyl transpeptidase plays a direct role in some hepatic and renal responses to injury. In the mouse γ-glutamyl transpeptidase is a single copy gene expressed from at least seven promoters, and many of the transcribed γ-glutamyl transpeptidase RNAs are restricted in their expression. Studies that combine analyses of cellular processes with a knowledge of gene structure and expression hold promise for unravelling how these two different levels of function are integrated.