THE MODE OF ACTION OF ALLICIN - TRAPPING OF RADICALS AND INTERACTION WITH THIOL-CONTAINING PROTEINS

Allicin (thio-2-propene-1-sulfinic acid S-allyl ester) is the main bio logically active component of garlic clove extracts. Its biological ac tivity was attributed to either antioxidant activity or thiol disulfid e exchange. Antioxidant properties of both allicin and its precursor, alliin (+ S-allyl-L-cysteine sulfoxide), were investigated in the Fent on oxygen-radical generating system [H2O2-Fe(II)]. Using the spin trap ping technique and ESR, it was found that both compounds possessed sig nificant antioxidant activity. The reaction between allicin and L-cyst eine was studied by H-1 and C-13-NMR, and a S-thiolation product, S-al lylmercaptocysteine, was identified. Allicin irreversibly inhibited SH -protease papain, NADP(+)-dependent alcohol dehydrogenase from Thermoa naerobium brockii (TBAD), and the NAD(+)-dependent alcohol dehydrogena se from horse liver (HLAD). All the three enzymes could be reactivated with thiol containing compounds. Papain could be reactivated with glu tathione, TBAD with dithiothreitol or 2-mercaptoethanol (2-ME) but not by glutathione, while HLAD could be reactivated only with 2-ME. This study demonstrates that in addition to its antioxidant activity, the m ajor biological effect of allicin should be attributed to its rapid re action with thiol containing proteins. (C) 1998 Elsevier Science B.V.