MICROSOMAL FORMATION OF S-NITROSOGLUTATHIONE FROM ORGANIC NITRITES - POSSIBLE ROLE OF MEMBRANE-BOUND GLUTATHIONE TRANSFERASE

The formation of S-nitrosoglutathione (GSNO) from amyl nitrite and n-b utyl nitrite was studied in rat liver microsomes, employing N-ethylmal eimide (MalNEt) as an activator and indomethacin as an inhibitor of mi crosomal glutathione S-transferase (GST). Rates were compared with GST activity measured with 1-chloro-2,4-dinitrobenzene (CDNB) as a substr ate. MalNEt stimulated GST activity and the formation of GSNO from amy l nitrite and n-butyl nitrite about 10-fold. Increasing concentrations of indomethacin inhibited both reactions in parallel. N-Acetyl-L-cyst eine but not L-cysteine could substitute for GSH. It is concluded that rat liver microsomal GST catalyses the formation of GSNO from amyl ni trite and n-butyl nitrite. The activity of the MalNEt-stimulated micro somal GST is calculated to be about 17 units/mg of enzyme with the alk yl nitrites and about 16 units/mg of enzyme with CDNB as a substrate, assuming that 3% of microsomal protein is GST. These rates are compara ble with those obtained for cytosolic GSTs. Thus microsomal GST may pl ay a significant role in the metabolism of alkyl nitrites in biologica l membranes.