[Kinetics of Fe2+-induced lipid peroxidation in liposomes in the presence of ascorbic acid. Concentrated effects of Fe2+ ions].

In order to study the kinetics of lipid peroxidation (LPO) at the stationary Fe2+ concentration the measurement of 2-thiobarbituric acid-reactive substances (TBARS) accumulation along with chemiluminescence (CL) in liposomes in the presence of ascorbic acid was used. It was shown that at 1 mM concentration of ascorbic acid the constant rate of LPO development occurred. In this system the direct determination of LPO rates at different Fe2+ concentrations were performed. The dependence of LPO rate on Fe2+ concentration was bell-shaped with a maximum at 50 microM. Probably, this value corresponds the "critical" ferrous ions concentration in a system. At 500 microM Fe2+ the LPO development was completely inhibited, but the addition of inorganic phosphate was found to start TBARS accumulation and CL development. The increase of phosphate concentration up to 500 microM produced the increase of LPO rate, however, at a higher phosphate concentrations LPO rate decreased. The biphasic effect of phosphate was completely similar to the decrease of Fe2+ concentration from the initial level (500 microM). It was proposed that the effect of phosphate is due to Fe2+ ion chelation in water solution leading to the remove some part of membrane-bound ferrous ions participating in LPO reactions, rather than changing of Fe2+ reactivity.