There is little information on the catalytic activity of Mb0
2 for unsaturated lipid oxidation. The catalytic function of Mb0
2 was compared with that of metMb for linoleate oxidation in aqueous dispersion at 5°C for one hr and pH 6.3. Oxidation of linoleate was estimated by determining the oxygen dissolved in the reaction mixture using an oxygen electrode.
Mb0
2 at a concentration of 5 or 10 μM had a catalytic effect similar to that of metMb in the early stage of the reaction, but became less effective than metMb in the later part of the reaction. NaN
3 inhibited the oxidation catalyzed by metMb but not that by Mb0
2. At 0.2 μM of catalyst, MbO
2 gave the same rate of linoleate oxidation as metMb and heat denatured Mb. NaN
3 had a little inhibitory effect on these catalyzed oxidations. The oxidations of linoleate catalyzed by both Mb0
2 and metMb at concentrations of 7 μM were inhibited more or less by the addition of BSA, ascorbic acid, cysteine, glutathion, and ribose but not by the addition of the following substances: glucose, nicotinic acid, nicotinamide, histidine, lysine, methionine, trimethylamine, and trimethylamine oxide.
From these results, it is postulated that MbO
2 has a catalytic function on unsaturated lipid oxidation comparable to that of metMb, especially at a lower concentration ratio of Mb to unsaturated lipid.
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