Metabolism of oestriol in vitro. Cofactor requirements for the formation of 2-hydroxyoestriol and 2-methoxyoestriol

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Abstract
The quantitative production of 2-hydroxyestriol and 2-methoxyestriol has been studied with rat-liver preparations. The 2-hydroxylase requires either a reduced diphosphopyridine nucleotide or reduced triphosphopyridine nucleotide-producing system and possibly a folic acid derivative. Adenosine triphosphate has a stimulating effect. The 2-hydroxylase is localized in the microsomal fraction. The 2-hydroxylase activity is absent in homogenates of kidney, ovary and uterus. There is no sex difference in the rat-liver activity. The O-methylating system requires magnesium ions, adenosine triphosphate and L-methionine. Evidence is presented that the o-methylase may be the same enzyme as that studied by Axelrod and Tomchick (1958). Preliminary evidence suggests that estrone, 17[alpha]-ethynylestradiol-17[beta], stilbestrol and possibly estradiol-17[beta] can be methoxylated in the position ortho to an existing phenolic group. 16-Oxo-estradiol-17[beta] and another unknown compound have been detected as minor metabolites of estriol. The estriol-16-hydroxy dehydrogenase is localized in the 1050OO g supernatant fraction. The relationship of reduced pyridine nucleotide, folic acid and adenosine triphosphate to hydroxylation reactions has been discussed.