Properties of estradiol 2-hydroxylase and 2-hydroxy-3-deoxyestradiol 3-hydroxylase in rat liver.

Abstract

The properties of enzyme systems involved in the formation of catechol estrogen from estradiol and 2-hydroxy-3-deoxyestradiol in rat liver microsomes have been investigated. Molecular oxygen dissolved in the incubation medium was enough for the occurrence of 2- and 3-hydroxylations. The presence of carbon monoxide suppressed the formation of catechol estrogen from the two substrates where the CO/O2 ratios needed for 50% inhibition of the bioconversion were 12.0 and 14.1, respectively. The inhibitory effect was reversed almost completely by illumination with white light. Pretreatment with phenobarbital and 3-methylcholanthrene did not exert any significant change in the activities of 2- and 3-hydroxylases, but increased the content of cytochrome P-450 or P-448 in liver microsomes. The storage of microsomal preparation in the frozen state resulted in a marked decrease in the hydroxylase activities. These results strongly imply that a similar cytochrome P-450 system would be operative in the formation of catechol estrogen from estradiol and 2-hydroxy-3-deoxyestradiol in rat liver microsomes.