Covalent modification of four isolated alkanninderivatives (alkannin, acetylalkannin, β, β-dimethylacrylalkannin and β- acetoxyisovalerylalkannin, respectively) on rabbit muscle latate dehydrogenase (LDHase) and yeast Alcohol Dehydrogenase (ADHase) has been studied. The quinone concentration curves show that the two enzymes are inhibited to different extents by the four alkannin derivatives. Assays of free amino groups and thiol groups in the enzymes indicate that the catalytic activities of LDHase and ADHase are mainly inhibited by covalent reaction of alkannin derivatives with thiol groups in enzymes. These results could be useful for investigating the biological mechanism of alkannin derivatives' cytotoxicity.

Key words: LITHOSPERMUM ERYTHRORRHIZON, NAPHTHQUINONE P, DEHYDROGENASE, MODIFICATION, DEHYDROGENASE, CYTOTOXICITY, COVALENT BONDS, NUCLEOPHILIC REAGENTS