Studies with Myoglobin Variants Indicate that Released Hemin Is the Primary Promoter of Lipid Oxidation in Washed Fish Muscle

Abstract

Variants of sperm whale myoglobin (Mb) were used to assess the mechanism of heme protein-mediated lipid oxidation in washed cod muscle. A myoglobin variant with high hemin affinity (V68T) was an exceptionally poor promoter of lipid oxidation, while a Mb variant with low hemin affinity (H97A) was a potent promoter of lipid oxidation. V68T releases hemin slowly due to the ability of threonine to hydrogen bond with coordinated water and the distal histidine within the heme crevice. H97A rapidly releases hemin because the relatively small alanine residue creates a channel for water to easily enter the heme crevice which weakens the covalent linkage of hemin to the proximal histidine. A variant sensitive to heme degradation (L29F/H64Q) was a weaker promoter of lipid oxidation compared to wild-type Mb. This suggests that degrading the heme ring and releasing iron decreased the ability of Mb to promote lipid oxidation. Free radicals resulting from hemin-mediated decomposition of lipid hydroperoxides have the capacity to propagate lipid oxidation and degrade hemin catalyst. This may explain why heme proteins behave as reactants rather than "catalysts" of lipid oxidation in washed cod. Collectively these studies strongly suggest that released hemin is the critical entity that drives heme protein-mediated lipid oxidation in washed fish muscle.

Redox Reactions of Myoglobin

“…Decreasing hemin affinity of met(III)Mb by site-directed mutagenesis [His(FG3) 97 Ala] increased lipid oxidation in washed muscle fibers at pH 5.7, whereas increasing hemin affinity [Val(E11) 68 Thr] decreased lipid oxidation (22). The relatively small and apolar alanine substitution at FG3 negates the electrostatic or hydrogen bonding interaction of His97 with the heme-7-propionate (Fig.…”

“…The ability of iron released from Mb to facilitate oxidative reactions compared to other oxidative forms of Mb (e.g., ferryl Mb) and dissociated ferriprotoporphyrin IX should be further investigated. Interestingly, a Mb mutant more susceptible to protoporphyrin IX degradation and iron release (H64Q/ L29F) promoted lipid oxidation in washed muscle less effectively compared to wild-type Mb at pH 5.7 (22). The exceptional ability of H64Q/L29F to remove H 2 O 2 produced by autoxidation should also inhibit lipid oxidation (1).…”

Apoglobin Stability Is the Major Factor Governing both Cell-free and in Vivo Expression of Holomyoglobin

“…In the absence of GdnHCl, unfolding leads to aggregation of the unfolded globin states (UH, U), making the process irreversible. Any released free hemin is highly toxic in vivo where it partitions into membranes and promotes lipid oxidation and generation of reactive oxygen species (7)(8)(9)(10).…”

Eff ects of natural antioxidants on colour stability, lipid oxidation and metmyoglobin reducing activity in raw beef patties

“…The reason behind such positive correlation may be that lipid oxidation produces peroxide material and free radicals which promote the pigment oxidation, resulting in meat discoloration (Cheng et al, 2007). On the other hand, pigment oxidation produces iron ion and promotes lipid oxidation (Grunwald and Richards, 2006). But not all studies that have measured lipid oxidation and myolobin oxidation in meat have produced results demonstrating that the two processes are linked (Faustman et al, 2010).…”