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Inhibition of rat steroid 5 alpha-reductase (isozyme 1) by suramin
M F Taylor1, A K Bhattacharyya, D C Collins
1Department of Biochemistry, College of Medicine, University of Kentucky, Lexington, USA.
Abstract:
In this study, we show the inhibition of rat steroid 5 alpha-reductase (isozyme 1) by suramin. The enzyme activity decreased in a dose-dependent manner as suramin concentrations increased with the calculated drug dose required for 50% inhibition (at 5 microM testosterone and 200 microM NADPH) being 13 microM. Suramin showed non-competitive inhibition of 5 alpha-reductase with respect to testosterone (KT1 = 2.4 microM) and competitive inhibition with respect to NADPH (KiNADPH = 220 nM). Furthermore, suramin and NADP+, but not NAD+, protected 5 alpha-reductase from labeling by 2-azido-NADP+, a photoactive probe which has recently been used to identify the NADPH binding domain of 5 alpha-reductase. These results suggest that suramin inhibits rat steroid 5 alpha-reductase (isozyme 1) at the level of NADPH binding to the enzyme.