Two distinct aromatase-active protein complexes are solubilized by use of deoxycholate and separated by diethylaminoethyl-cellulose chromatography from lyophilized powder of 900 X g precipitate fraction of human term placenta. Aromatase activity to produce estriol, the major estrogen of human pregnancy, was designated to be aromatase I activity and measured by estriol formation from 16α-hydroxytestosterone. Aromatase II activity was the designation for that which produces estrone plus estradiol and was measured by androstenedione aromatization. Aromatases II and I are eluted with 0.25 m and 0.5 m Tris buffer, respectively, from diethylaminoethyl-cellulose column in an Mr 2 million soluble complex. Each has a minimum active Mr 135,000 subunit, which is isolated by Bio-Gel filtration in the presence of detergents, and consists of a reduced nicotinamide adenine dinucleotide phosphate:cytochrome P-450 reductase (Mr 83,000) and a cytochrome P-450 (Mr 52,000). Aromatase II was found to be the major aromatase, containing approximately five times more aromatase activity, reduced nicotinamide adenine dinucleotide phosphate:cytochrome c reductase activity, cytochrome P-450, and protein than did aromatase I. Antibodies raised in rabbits against aromatase II and its reductase suppressed aromatase II activity of breast cancer tissues, as well as of adult male lung tissue, placental microsomes, and solubilized aromatase. The breast carcinoma specimens responded to the antibodies in different degrees, but there was no response to antibodies against rat liver cytochrome P-450. The results indicate similar antigenic structures for breast cancer and placental aromatase but not for rat liver cytochrome P-450.

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Presented at the Conference “Aromatase: New Perspectives for Breast Cancer,” December 6 to 9, 1981, Key Biscayne, Fla. Preliminary accounts on isolation of 2 placental aromatases have been presented at the 60th Annual Meeting of the Endocrine Society, June 1978, Miami, Fla., and the Fourth International Symposium on Microsomes and Drug Oxidations, July 1979, Ann Arbor, ich. This research was supported in part by USPHS Grants HD-04945 and RR-05716 and the James H. Cummings Foundation, Inc.

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