Formation of 6β-hydroperoxyprogesterone in rat liver microsomes

Abstract

To verify the concept that molecular oxygen can be enzymically introduced as such into the steroid nucleus, radioactive progesterone and also 5-pregnene-3,20-dione were incubated with microsomal preparations of rat liver. In both cases, a significant amount of radioactive 6β-hydroperoxyprogesterone was isolated, together with 6β-hydroxyprogesterone and 6-oxoprogesterone. Addition of p-hydroxymercuribenzoate or mercurichloride significantly inhibited the formation of the hydroperoxide, whereas potassium cyanide and carbon monoxide were only partially inhibitory. Addition of 6β-hydroperoxyprogesterone to cytochrome P-450 containing fractions of hepatic microsomes induced a Type 1 difference spectrum characterized by an absorption maximum at 392 nm. a minimum at 420 nm, and an isosbestic point at 407 nm. At 4°C. its apparent dissociation constant was found to be in the same order of magnitude as that of 6β-hydroxyprogestcrone, namely 1.33 μM. A new pathway in rat liver for the formation of both 6β -hydroxyprcgesterone and 6-oxoprogesterone via the 6β-hydroperoxide as a common precursor, is proposed.