Purification and Characterization of Membrane-Bound Prostaglandin E Synthase from Bovine Hearts

Abstract

E series of prostaglandin (PG)s were first discovered in sheep seminal vesicles. PGE₂is widely distributed in various organs, and exhibits various biological activities such as smooth muscle dilatation/contraction, Na+ excretion, body temperature regulation, inhibition of gastric acid secretion, and inhibition of immune responses. PGE synthase (EC. 5. 3. 99. 3.) catalyzes the conversion of PGH₂to PGE₂. Although several groups have attempted to purify this enzyme for the last 20 years, the membrane-bound PGE synthase has not yet been purified to homogeneity from microsomes of any tissues. In 1997, we reported that PGE synthase activity is widely distributed in the microsomal fractions of rat organs (1). Most of the PGE synthase activities in these organs absolutely required glutathione (GSH). In contrast, the enzyme activity in the heart, spleen, and uterine microsomes required SH-reducing reagents including dithiothreitol (DTT), GSH, or ß-mercaptoethanol (β-Mer), but the requirement for its catalytic activity was not specific for GSH. We purified the GSH-independent PGE synthase from bovine heart to apparent homogeneity, and examined its molecular and catalytic properties (2).