Redox reactions of myoglobin.
CONCLUSIONS
Failure to maintain myoglobin (Mb) in the reduced state causes the formation of metMb, ferryl Mb species, and cross-linked Mb. Dissociation of ferriprotoporphyrin IX from the globin and release of iron atoms can also occur as oxidized Mb accumulates. These modifications may contribute to various oxidative pathologies in muscle and muscle foods.


BACKGROUND
The mechanism of ferryl Mb-mediated oxidative damage to nearby structures has been partially elucidated. Dissociation of ferriprotoporphyrin IX from metMb occurs more readily at acidic pH values. The dissociated ferriprotoporphyrin IX (also called hemin) readily decomposes preformed lipid hydroperoxides to reactive oxygen species. Heme oxygenase as well as lipophilic free radicals can degrade the protoporphyrin IX moiety, which results in the formation of free iron.


RESULTS
The multiple pathways by which Mb can incur toxicity create difficulties in determining the major cause of oxidative damage in a particular system. Peroxides and low pH activate each of the oxidative Mb forms, ferriprotoporphyrin IX, and released iron. Determining the relative concentration of these species is technically difficult, but essential to a complete understanding of oxidative pathology in muscle tissue.


CONCLUSIONS
Improved methods to assess the different pathways of Mb toxicity are needed. Although significant advances have been made in the understanding of Mb interactions with other biomolecules, further investigation is needed to understand the physical and chemical nature of these interactions.
Meat Science and Muscle Biology Laboratory, Department of Animal Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA. mprichards@ansci.wisc.edu
Mark P
MP
Richards
D006427:Hemin / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000378:metabolism; D009211:Myoglobin / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010545:Peroxides / Q000378:metabolism; D011485:Protein Binding
D009211:Myoglobin; D010545:Peroxides; D006427:Hemin; D007501:Iron