ISOFORM-SPECIFIC BIOTRANSFORMATION OF GLYCERYL TRINITRATE BY RAT AORTIC GLUTATHIONE S-TRANSFERASES

The objective of this study was to purify and characterize rat aortic glutathione S-transferases (GSTs) and to assess their role in the biot ransformation of the nitrovasodilator, glyceryl trinitrate (GTN). Two class alpha GSTs (Ya and Yc) a class mu GST (Yb-2) and a class pi GST (Yp) were identified in rat aortic cytosol. Partial purification of th ree of these (Yb-2, Yc and Yp) was achieved by affinity chromatography with S-hexylglutathione agarose. Further purification by cation- and anion-ex change chromatography resulted in the purification of GST Yc and GST Yb-2/Yp to apparent homogeneity, a purification of 200- and 11 0-fold, respectively. Purified GST Yc and Yb-2/Yp mediated GTN biotran sformation with similar rates. GST activity and GTN biotransformation by rat aortic cytosol and affinity-purified GSTs were highly sensitive to inhibition by the class mu selective inhibitors Basilen Blue and b romosulfophthalein. Removal of GST Yb-2 from rat aortic cytosol by imm unoprecipitation resulted in marked inhibition of GST activity and GTN biotransformation. We conclude that the GSTs account for the major po rtion of GTN biotransformation in rat aortic cytosol, and that this is primarily attributable to the GST Yb-2 isoform.