ON A COENZYMATIC FUNCTION OF ESTRADIOL-17β

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Abstract
Purified estradiol-17[beta]-hydroxy-steroid dehydrogenase was isolated from human placenta and in the presence of stoichiometric quantities of estradiol-17[beta], the enzyme reduces DPN, TPN, APDPN, pyridinealdehyde-DPN, but not desamino-DPN. In the presence of stoichiometric amounts of pyridine nucleotides and catalytic concentrations of steroid hormones, the enzyme promotes a reversible hydrogen transfer between the pyridine nucleotides. During this process the hormone is alternately oxidized and reduced indicating that it acts in the manner of a hydrogen carrier or coenzyme. Evidence is presented for the identity of the protein catalyzing dehydrogenase and transhydrogenase functions. Detailed measurements of the binding constants of the enzyme for the naturally occurring pyridine nucleotides and several synthetic analogs are given. The authors feel that many of the biochemical consequences of steroid hormones may be related to their action as coenzymes of transhydrogenation and the implications of this hypothesis are discussed in detail.