S-Nitrosoglutathione as a substrate for γ-glutamyl transpeptidase

Abstract

S-Nitrosoglutathione (GSNO) has been used as a nitric oxide (•NO) donor compound and has also been postulated to be involved in the transport of •NO in vivo. In this study we have examined the possibility that GSNO is a substrate for γ-glutamyl transpeptidase (γ-GT), an enzyme that hydrolyses the γ-glutamyl moiety of glutathione to give glutamate and cysteinylglycine. γ-GT accelerated the decomposition of GSNO, forming S-nitrosocysteinylglycine (CG-SNO) by a mechanism inhibitable by the γ-GT inhibitors acivicin and S-methylglutathione. The Km of γ-GT for GSNO was found to be 28 μM. In the presence of contaminating transition metal ions, γ-GT accelerated the release of •NO from GSNO, as CG-SNO is more susceptible to transition metal ion-dependent decomposition than GSNO. However, in the presence of the transition metal ion chelator diethylenetriaminepentaacetic acid, neither GSNO nor CG-SNO decomposed to generate •NO. Neither S-methylglutathione nor acivicin affected the vasodilatory response to GSNO in an isolated perfused rat heart. However, rat kidney homogenate stimulated the decomposition of GSNO by an acivicin-inhibitable mechanism. It is likely therefore that γ-GT is involved in the decomposition of GSNO in the kidney but not in the heart.