ACTIVATION OF HYDROGEN TRANSFER BETWEEN PYRIDINE NUCLEOTIDES BY STEROID HORMONES

Abstract

Soluble enzyme preparations of human placenta promote the transfer of hydrogen from TPNH to DPN in the presence of minute amounts of certain steroid hormones. The same enzyme preparations also catalyze the oxidation of these steroids by both forms of pyridine nucleotide. Evidence is presented for the identity of a placental hydroxysteroid dehydrogenase with the transhydrogenase activity. It is proposed that the metabolic function of hydroxysteroid dehydrogenases with dual pyridine nucleotide specificity is to act as pyridine nucleotide transhydrogenases. Properties of some hydroxysteroid dehydrogenases which favor transhydrogenation are: their high affinity and specificity for particular steroids; their ability to react with both DPN and TPN; and, the suitable equilibria between steroid alcohols and ketones which obtain at physiological hydrogen ion concentrations.