Demonstration of a thyrotropin-responsive prostaglandin E2-9-ketoreductase in bovine thyroid.

1. Prostaglandin E2-9-ketoreductase activity was demonstrated in bovine thyroid homogenates. 2. The enzyme requires reduced pyridine nucleotide and dialysis prior to assay for optimal activity. 3. The products of the reaction, NADP and prostaglandin F2alpha, inhibit enzyme activity. 4. Sigmoidal kinetics are observed when substrate concentration is plotted against enzyme velocity, indicative of an allosteric enzyme. 5. Thyrotropin increases enzyme activity in bovine thyroid slices. This increase is both hormone- and tissue-specific.