ANTIOXIDANT ACTIVITY OF REDUCED MENADIONE IN SOLVENT SOLUTION AND IN MODEL MEMBRANES

The antioxidant activity of reduced menadione was investigated and com pared with that of alpha-tocopherol both in solvent solution and in la rge unilamellar vesicles by using azocompounds as free radical generat ors. The results show that: i) reduced menadione behaves as a chain-br eaking antioxidant; ii) its inhibition rate constant is similar to tha t of alpha-tocopherol in homogeneous solution, whereas it is 4 times l arger in egg yolk lecithin vesicles; iii) the stoichiometric factor is found lower than 1 in both systems, since a substantial portion of me nadiol is consumed by autoxidation and does not contribute to radical trapping; iv) when both alpha-tocopherol and menadiol are present in v esicles, reduced menadione can spare alpha-tocopherol. Data presented here suggest that the reduced form of vitamin K may protect, when pres ent, cellular membranes from free radical damage.