Co-oxidation of salicylate and cholesterol during the oxidation of metmyoglobin by H 2O 2

Abstract

The reaction between metmyoglobin and H 2O 2 proceeds with oxidation of the hemoprotein iron to a higher valence state and consumption of the peroxide. This reaction is further associated with (a) O 2 evolution; (b) hydroxylation of the aromatic compound salicylate to yield a set of dihydroxybenzoic acid derivatives (analyzed by HPLC with electrochemical detection); (c) autoxidation of cholesterol with formation of 3β-hydroxy-5-α-cholest-6-ene-5-hydroperoxide; and (d) formation of electronically excited states detected by low-level chemiluminescence. The heterolytic scission of the O-O bond of hydroperoxides by metmyoglobin causes the formation of an oxidizing equivalent capable of promoting peroxidation of linoleate and arachidonate (as indicated by the parallel formation of thiobarbituric acid-reactive material and an enhancement of chemiluminescence intensity). The identity of the oxidizing equivalent(s) is discussed in terms of the formation of a relatively stable higher state of oxidation of heme Fe (Fe IV-OH or Fe VO) as well as on possible intermediate species derived during the decomposition of H 2O 2 by metmyoglobin, such as HO and 1O 2. These species might be involved either simultaneously or sequentially in the peroxidation of fatty acids as well as in the tissue damage associated with the formation of H 2O 2 in ischemic-reperfusion States.