Mechanisms of lipid peroxide formation in tissues Role of metals and haematin proteins in the catalysis of the oxidation of unsaturated fatty acids

Abstract

Oxidation of unsaturated fatty acids such as linoleic acid and linolenic acid is catalysed by metals at 37° in the pH range 4.5–7.5 with the formation of peroxides. Co 2+ and Mn 2+ are very active catalysts whilst Cu 2+, Fe 3+ and Fe 2+ are weakly active. The catalytic activity of Fe 3+ can be strongly stimulated by addition of ascorbic acid or cysteine but both these substances delay oxidation catalysed by Co 2+ or by haematin proteins. The pH optimum for oxidation catalysed by Fe 3+ plus ascorbic acid is 5.5, for Co 2+ catalysis it is 6.5 but haemoglobin-catalysed oxidation is unaffected by pH over the range 4.5 to 8.0. o-Phenanthroline and 8-hydroxyquinoline powerfully inhibit Co 2+-catalysed oxidation but powerfully stimulate Fe 3+-catalysed oxidation. Co 2+-catalysed oxidation is unaffected by most amino acids but is strongly inhibited by histidine, by serum albumin and by some other proteins. It is considered that, in vivo, lipid peroxide formation is likely to be a result of oxidation of unsaturated lipids. catalysed by Fe 3+ and a reducing agent such as ascorbic acid or by heamatin proteins.