Reactivity of metmyoglobin towards phospholipid hydroperoxides

Ferrylmyoglobin, the high oxidation state of myoglobin analogous to compound II of peroxidases, promotes the peroxidation of palmitoyl-linoleyl-phosphatidylcholine (PLPC) large unilamellar vesicles. This was associated with oxygen consumption and a slow conversion of ferrylmyoglobin to metmyoglobin. The time course of oxygen consumption was characterized by the occurrence of a lag phase, which could be overcome by the addition of sodium deoxycholate to the reaction mixture. The rate of conversion of ferrylmyoglobin to metmyoglobin was slower than that of oxygen consumption, and there was not stoichiometric correlation between both events. These findings suggest that the observed oxygen consumption linked to lipid peroxidation is supported by a peroxidatic activity encompassed by the ferrylmyoglobin<==>metmyoglobin transition as well as free radical propagation reactions. Incubation of metmyoglobin with PLPC vesicles containing 3% hydroperoxide resulted in oxygen consumption, the time course of which was devoid of the lag phase observed with hydroperoxide-free unilamellar lipid vesicles. The incubation of metmyoglobin with peroxide-containing PLPC vesicles or with equimolar amounts of lipid hydroperoxide was not associated with Soret or visible absorption spectral changes of metmyoglobin, which could be ascribed to its conversion to ferrylmyoglobin. Treatment of the metmyoglobin/lipid hydroperoxide mixtures with Na2S did not lead to the formation of the sulfheme protein derivative, which can be considered as a fingerprint for the occurrence of ferrylmyoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)