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17β-Hydroxysteroid oxidoreductase, the enzyme that catalyses the interconversion of oestradiol and oestrone, is known to be present in human breast tissue. However, it is not known whether one or more forms of the enzyme is present. Homogenates of breast adipose tissue and breast glandular tissue were fractionated and fractions assayed in the oxidative direction with NAD⁺ and NADP⁺ as coenzymes, and in the reductive direction with NADH and NADPH as coenzymes. Ultracentrifugation of homogenates showed that there was membrane-bound activity and soluble activity. The soluble activity was due to a number of forms of the enzyme with different molecular weights, three in breast adipose tissue and two in breast glandular tissue, as shown by fractionation with (NH₄)₂SO₄ followed by chromatography on Sephadex G-200. The forms of the enzyme isolated differed in their affinities for substrates and coenzymes and in the relative rates at which they catalysed the oxidative and reductive reactions. Preliminary experiments with breast tumours showed that they also contained membrane-bound activity and more than one soluble form of the enzyme.

This article has been cited by other articles:

				M. Bonenfant, C. H. Blomquist, P. R. Provost, R. Drolet, P. D’Ascoli, and Y. Tremblay Tissue- and Site-Specific Gene Expression of Type 2 17{beta}-Hydroxysteroid Dehydrogenase: In Situ Hybridization and Specific Enzymatic Activity Studies in Human Placental Endothelial Cells of the Arterial System J. Clin. Endocrinol. Metab., December 1, 2000; 85(12): 4841 - 4850. [Abstract] [Full Text]