The simultaneous hydrolysis of glutathione and glutamine by rat kidney gamma-glutamyltransferase.

The simultaneous hydrolysis of L-glutamine and glutathione by rat kidney gamma-glutamyltransferase has been studied. At concentrations of the two substrates giving rates approximating to Vmax, it is shown that glutamine hydrolysis predominates. Under saturating conditions for both substrates, 65% of the glutamic acid produced is derived from glutamine. Using [14C]glutamine it is also shown that at physiological plasma concentrations of glutamine (in excess of 400 microM) and glutathione (20 microM) glutamine hydrolysis is the predominating reaction. We therefore suggest that both glutamine and glutathione are important in vivo donors for gamma-glutamyltransferase.