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Identification of initiating agents in myoglobin-induced lipid peroxidation
E S Newman1, C A Rice-Evans, M J Davies
1Department of Biochemistry, St Thomas' Hospital-UMDS, London, U.K.
Abstract:
Reaction of metmyoglobin with peroxides is known to involve the formation, possibly via a porphyrin radical-cation, of a ferryl (iron(IV)-oxo) species and a protein radical; there is a little information available as to which of these species initiates the damage which is observed on incubating membrane fractions with such mixtures. It is shown in this study that the initial protein radical, which is a tyrosine phenoxyl radical centered at position 103 in the protein, does not react rapidly with erythrocyte membranes. However a tyrosine peroxyl radical, formed by addition of oxygen to this species, does react rapidly, and it is concluded that this radical, together with the ferryl species, is an important initiating species in myoglobin-induced lipid peroxidation.
Insights
Metmyoglobin reacts with peroxides to form damaging ferryl and protein radicals. A tyrosine peroxyl radical, derived from the initial protein radical, rapidly initiates lipid peroxidation in erythrocyte membranes.
Area of Science:
- Biochemistry
- Oxidative Stress
- Protein Chemistry
Background:
- Metmyoglobin reactions with peroxides can generate reactive species.
- The exact mechanism of myoglobin-induced membrane damage is not fully understood.
- Identifying the initiating species is crucial for understanding oxidative damage.
Purpose of the Study:
- To determine which reactive species initiate myoglobin-induced lipid peroxidation in erythrocyte membranes.
- To elucidate the role of protein radicals in oxidative damage.
Main Methods:
- Incubation of membrane fractions with metmyoglobin and peroxides.
- Characterization of reactive intermediates, including protein radicals.
- Assessing the reactivity of different radical species with erythrocyte membranes.
Main Results:
- The initial protein radical (tyrosine phenoxyl radical at position 103) showed slow reactivity with membranes.
- A subsequent tyrosine peroxyl radical, formed by oxygen addition, reacted rapidly with membranes.
- Both the ferryl species and the tyrosine peroxyl radical were identified as key initiating species.
Conclusions:
- The tyrosine peroxyl radical, not the initial protein radical, is a primary initiator of myoglobin-induced lipid peroxidation.
- Ferryl species and tyrosine peroxyl radicals are critical in initiating membrane damage.
- Understanding these mechanisms is vital for addressing oxidative stress-related conditions.