ISOLATION AND CHARACTERIZATION OF HYDROXYMETHYLGLUTARYL COENZYME-A REDUCTASE INHIBITORS FROM FERMENTED SOYBEAN EXTRACTS

The present study was carried out to isolate and identify the 3-hydrox y-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase)-inhibiting agents in the lipids of fermented soybeans, Tempeh, since oral feedin g of an alcohol extract of Tempeh to hypercholesterolemic rabbits redu ced their level of serum cholesterol. Fermented soybeans were extracte d with hexane:ethanol, and the extract was separated into different fr actions by silica gel column chromatography. One fraction obtained, SF 1, inhibited the rat liver microsomal enzyme 94% at a dose of 0.625 mu g lipid/mu l of incubation contents; 0.17 mu g/mu l lead to 50% inhib ition. Analysis of SF1 by gas chromatography/mass-spectrometry and fas t-atom-bombardment (FAB)/mass-spectrometry revealed the presence of pa lmitic, stearic, oleic, linolenic, arachidic, and behenic acids. Oleic acid inhibited HMG-CoA reductase 94% at a dose of 0.625 mu g/mu l of incubation contents, and 0.055 mu g/mu l inhibited 50% of the enzyme a ctivity. Enzyme kinetics showed the inhibition was of a mixed type. Li nolenic acid, 0.625 mu g/mu l of incubation contents, inhibited the en zyme 100%; and 0.085 mu g/mu l lead to 50% inhibition. The inhibition was competitive. The other fatty acids were less inhibitory (1-18%). M ethyl esters of oleic acid and linolenic acid maximally inhibited the enzyme 20 and 15%, respectively.