Myoglobin reactions

Aside from the classical examples of hemoglobin and myoglobin, reaction of ferrous heme iron with O2 in hemeperoxidases has been reported for myeloperoxidase [60], horseradish peroxidase C [62], bovine liver catalase [68], lignin peroxidase [46], and lactoperoxidase [61]. With the exception of lactoperoxidase, the binding of O2 is irreversible and CIII engages in one or more of the decay pathways described below. 

Although cytochrome 65 could be a physiological partner of ferritin, neither of the cytochromes c are possible physiological partners, and the myoglobin reaction is so slow, because of the intrinsic reactivity of myoglobin, that this is unlikely to be a significant reaction in vivo. 

Recent studies on the analogous myoglobin reactions have suggested that a highly resonance-stabilized radical that is trapped via the C-3 position on the indole ring (108, 110), can be formed on the... 

Theorell [4], and hemocyanin. The rate of the oxygen-myoglobin reaction of 2 X lOVrosec was accurately determined, a reaction as fast as any which has been studied by flow-mixing methods. This line of work came to an end with Millikan s untimely death in a climbing accident, and his apparatus has never been replicated, although it was preserved for many years in Roughton s laboratory. 

Fig. 12.16. Myoglobin reactions (Mb myoglobin, MMb+ metmyoglobin, Mb02 oxymyoglobin, MbNO nitrosylmyoglobin, MMb+NO nitrosylmetmyo-globin)...

The myoglobin reactions relevant to meat color are presented schematically in Fig. 12.16. 

Elber R and Karplus M 1987 A method for determining reaction paths in large molecules application to myoglobin Chem. Phys. Lett. 139 375... 

Elber R and M Karplus 1987. A Method for Determining Reaction Paths in Large Molecules Application to Myoglobin. Chemical Physics Letters 139 375-380. 

The abihty of iron to exist in two stable oxidation states, ie, the ferrous, Fe ", and ferric, Fe ", states in aqueous solutions, is important to the role of iron as a biocatalyst (79) (see Iron compounds). Although the cytochromes of the electron-transport chain contain porphyrins like hemoglobin and myoglobin, the iron ions therein are involved in oxidation—reduction reactions (78). Catalase is a tetramer containing four atoms of iron peroxidase is a monomer having one atom of iron. The iron in these enzymes also undergoes oxidation and reduction (80). 

Steady-state equation. Given what was said about the reduction of Mn(myoglobin)+ by dithionite ions2 [Eq. (6-3)] in Section 6.2, construct a reaction scheme. How is k of Eq. (6-4) related to the constants of your proposal ... 

Cytochrome c is a heme containing protein which occurs in muscle at lower concentrations than does myoglobin. It was demonstrated some time ago (18) that oxidized cytochrome c reacts with gaseous nitrite oxide to produce a nltrosyl compound. Recent work (19, 20, 21) has examined the reactions of cytochrome c with nitrite and the contribution of the product formed to cured meat color in considerably more detail. The general conclusion is that even at the pH normally encountered in meat, the reaction can take place in the presence of ascorbic acid but probably does not affect meat color because of the unstable nature of the reaction product and the low concentration. 

Bolton, J. L. Le Blanc, J. C. Y. Siu, K. W. M. Reaction of quinone methides with proteins analysis of myoglobin adduct formation by electrospray mass spectrometry. Biol. Mass... 

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