Metabolism of glycyrrhetic acid by rat liver microsomes: glycyrrhetinate dehydrogenase.
Glycyrrhetic acid, derived from a main component of liquorice, was converted to 3-ketoglycyrrhetic acid reversibly by rat liver homogenates in the presence of NADPH or NADP+. Glycyrrhetic acid-oxidizing and 3-ketoglycyrrhetic acid-reducing activities were localized in microsomes among the subcellular fractions of rat liver. Glycyrrhetic acid-oxidizing activity and 3-ketoglycyrrhetic acid-reducing activities showed pH optima at 6.3 and 8.5, respectively, and required NADP+ or NAD+ and NADPH or NADH, respectively, indicating that these activities were due to glycyrrhetinate dehydrogenase. The dehydrogenase was not solubilized from the membranes by the treatment with 1 M NaCl or sonication, indicating that the enzyme is a membrane component. The dehydrogenase was solubilized with detergents such as Emalgen 913, Triton X-100 and sodium cholate, and then separated from 3 beta-hydroxysteroid dehydrogenase (5 beta-androstan-3 beta-ol-17-one-oxidizing activity) by butyl-Toyopearl 650 M column chromatography. Partially purified enzyme catalyzed the reversible reaction between glycyrrhetic acid and 3-ketoglycyrrhetic acid, but was inactive toward 3-epiglycyrrhetic acid and other steroids having the 3 beta-hydroxyl group. The enzyme required NADP+ and NADPH for the highest activities of oxidation and reduction, respectively, and NAD+ and NADH for considerable activities, similar to the results with microsomes. From these results the enzyme is defined as glycyrrhetinate dehydrogenase, being quite different from 3 beta-hydroxysteroid dehydrogenase of Ruminococcus sp. from human intestine, which is active for both glycyrrhetic acid and steroids having the 3 beta-hydroxyl group.
Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Japan.
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D015096:3-Hydroxysteroid Dehydrogenases / Q000302:isolation & purification; D000429:Alcohol Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002855:Chromatography, Thin Layer; D006034:Glycyrrhetinic Acid / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
D015096:3-Hydroxysteroid Dehydrogenases; D000429:Alcohol Oxidoreductases; C056636:3-alpha-hydroxyglycyrrhetinate dehydrogenase; D006034:Glycyrrhetinic Acid