PGD2 formation in the vasculature: characteristics of rat tail vein prostaglandin endoperoxide-D isomerase.

Rat tail vein homogenates, microsome and high speed supernatant fractions were incubated with [1-(14) C]prostaglandin endoperoxide (PGH2) and products separated and identified by radio-thinlayer chromatography. PGI2 synthase was localized to the microsomal fraction, but exhibited low activity compared to rat tail arteries prepared in the same manner. PGH-D isomerase was identified in the cytosolic fraction of tail veins. The isomerase was maximally active in the presence of reduced glutathione at pH 7.5-8.0, exhibited a Km for PGH2 of 33 microM, and was inhibited sulfhydryl-directed reagents. The similarities of this enzyme to PGD synthase of the rat cerebral microvasculature are discussed.