Metabolism of prostaglandins E, A, and C in serum

Three prostaglandin-metabolizing enzymes were detected in human serum. One enzyme was a dehydrase that converted prostaglandin E to prostaglandin A, the second was a prostaglandin A isomerase that converted prostaglandin A to prostaglandin C and the third was a prostaglandin C isomerase that converted prostaglandin C to prostaglandin B. All three were inactivated by sulfhydryl blocking agents. In human serum, only prostaglandin C isomerase had high activity, whereas the two other enzymes had very low activity. In rabbit serum both isomerases were very active, but dehydrase activity could not be detected. Prostaglandin C isomerase activity was also found in crystallized human serum albumin and rabbit serum albumin.