Differences in the antioxidant mechanism of carnosine in the presence of copper and iron

Carnosine is a beta-alanylhistidine dipeptide found in skeletal muscle. Carnosine (1.0-25 mM) is capable of inhibiting copper- and iron-catalyzed oxidation of phosphatidylcholine liposomes as measured by thiobarbituric acid reactive substances (TBARS) and lipid peroxides. The ability of 5 mM carnosine to inhibit the formation of TBARS and lipid peroxides was 2.5- and 8.8-fold higher, respectively, for copper- than iron-catalyzed lipid oxidation. Carnosine (0.05-10.0 mM) is capable of inhibiting copper-catalyzed oxidation of ascorbic acid but was ineffective at preventing iron-catalyzed ascorbate oxidation. Carnosine inhibits iron-dependent microsomal lipid oxidation but does not inhibit the oxidation of NADPH by the enzyme system. 1H NMR spectra of carnosine show peak broadening in the presence of copper but not iron. These data suggest that carnosine forms a complex with copper which decreases its catalytic activity; however, carnosine does not form a complex with iron