Synthesis of 6-keto-PGF1alpha by ram seminal vesicle microsomes

At low substrate/enzyme ratios, and in the absence of reduced glutathione (GSH), the major prostaglandin (PG) biosynthesised by the ram seminal vesicle cyclo-oxygenase from arachidonic acid was 6-keto-PGF1alpha. The addition of nanomolar amounts of reduced GSH suppressed biosynthesis of this product and stimulated the formation of PGE2; 1-epinephrine enhanced the conversion of the substrate but had no effect on the type of product formed. 15-Hydroperoxy arachidonic acid selectively inhibited formation of 6-keto-PGF1alpha (IC50 100 muM) but blocked synthesis of all cyclo-oxygenase products at concentrations greater than 1 mM. At substrate concentrations of muM or greater, synthesis of 6-keto-PGF1alpha was inhibited and PGE2 and PGF2alpha were the main products formed.