부산대학교 도서관

The 4-hydroxy metabolite of 17[Beta]-estradiol ([E.sub.2]) has been implicated in the carcinogenicity of this hormone. Previous studies showed that aryl hydrocarbon-receptor agonists induced a cytochrome P450 that catalyzed the 4-hydroxylation of [E.sub.2]. This activity was associated with human P450 1B1. To determine the relationship of the human P450 1B1 gene product and [E.sub.2] 4-hydroxylation, the protein was expressed in Saccharomyces cerevisiae. Microsomes from the transformed yeast catalyzed the 4- and 2-hydroxylation of [E.sub.2] with [K.sub.m] values of 0.71 and 0.78 [[micro]molar] and turnover numbers of 1.39 and 0.27 nmol product [min.sup.-1[[center dot]nmol [P450.sup.-1], respectively. Treatment of MCF-7 human breast cancer cells with the aryl hydrocarbon-receptor ligand indolo[3,2-b]carbazole resulted in a concentration-dependent increase in P450 1B1 and P450 1A1 mRNA levels, and caused increased rates of 2-, 4-, 6[Alpha]-, and 15[Alpha]-hydroxylation of [E.sub.2]. At an [E.sub.2] concentration of 10 nM, the increased rates of 2- and 4-hydroxylation were approximately equal, emphasizing the significance of the low [K.sub.m] P450 1B1-component of [E.sub.2] metabolism. These studies demonstrate that human P450 1B1 is a catalytically efficient [E.sub.2] 4-hydroxylase that is likely to participate in endocrine regulation and the toxicity of estrogens.