The prostaglandin synthetase system of bovine vesicular gland microsomes was solubilized and separated into Fractions I and II. The former fraction catalyzed the conversion of 8,11,14-eicosatrienoic acid to prostaglandin H1 (9 alpha, 11alpha-epidioxy-15(S)-hydroxy-13-trans-prostenoic acid). This compound was isomerized to prostaglandin E1 (11alpha, 15(S)-dihydroxy-9-keto-13-trans-prostenoic aci...