Zearalenone reductase from rat liver.

Zearalenone is known to be reduced by rat liver preparations to a more active estrogenic metabolite, alpha-zearalenol. To elucidate the enzymatic feature of zearalenone reductase, we worked out a simple assay procedure for this enzyme using [3H]-zearalenone and thin layer chromatography (TLC). The NAD(P)H-dependent zearalenone reductase localized in the microsomes was most active at pH 4-4.5, while the reductase localized in the cytosol was active at neutral pH. The former enzyme reduced zearalenone only to alpha-zearalenol and the latter reduced both alpha-zearalenol and beta-zearalenol. The microsomal enzyme was solubilized with Triton X-100 and purified by DEAE-Sephadex, hydroxyapatite and Sepharose 4B column chromatographies. The partially purified enzyme showed the following properties. a) The molecular weight of the enzyme was estimated to be about 230,000 by Sepharose 4B chromatography. b) The apparent Km value of the enzyme was 1.0 X 10(-5) M for zearalenone at an NADPH concentration of 1 mM. c) The enzyme activity was inhibited by a high concentration of KCl but not by 1 mM Co2+, Mn2+, Zn2+, EDTA, or 20 mM N-ethylmaleimide.