Ferric myoglobin

Compared with Molsidomine, both SIN-1 and SIN-1A are reported to induce similar, but more rapid hypotensive action [95, 96]. SIN-1A, after undergoing oxidation in the presence of oxygen or, in vivo, possibly by redox-active enzymes such as cytochrome C [97, 98] or by reaction with ferric myoglobin formed during reperfusion injury [99], releases NO through an intermediate radical cation. 

If this interpretation is correct, then the rate of spin state transitions in these systems will depend on the reorganization energy requirements. Two examples will be described. Ferric myoglobin undergoes a... 

SCHEME 4.2 Formation of nonequilibrium hexacoordinated ferrous myoglobin (2) as a result of cryoreduction of ferric myoglobin (1). Annealing of (2) above 180K results in protein relaxation to the pentacoordinated high-spin ferrous form (3). 

The proposed mechanism of NO release is shown in Scheme 1. Molsidomine (31) is converted to SIN-1 (32) by the action of liver esterases. SIN-1 (32) undergoes oxidation in the presence of oxygen or, in vivo, possibly by redox enzyme such as cytochrome c or by ferric myoglobin to release NO through a radical cation. 

Haem electronic structure in deoxy myoglobin Acid-alkaline transition in ferric myoglobin Oxy and carbonmonoxy myoglobins F relaxation mechanism... 

Whether lipid oxidation in muscle foods is catalysed by the iron redox cycle or by formation of the ferryl ions is not clear. However, ferrous ions react with lipid hydroperoxides much faster than with hydrogen peroxide. As shown above, if the reaction of metmyoglobin with hydroperoxides produces ferryl radicals capable of initiating lipid oxidation, it is necessary to prevent the formation of metmyoglobin or methemoglobin. At acidic pH, ferric myoglobin can initiate lipid oxidation in the presence of lipid hydroperoxides. 

Figure 12 The reaction between the cyanide complex of ferric myoglobin (horse heart) and sodium dithionite. A subset of the total number of spectra collected is shown. An initial increase in absorbance is seen at 435 nm and in the visible region, spectra displayed every 20 ms, followed by a slower decrease, only the final spectrum (thicker line) is shown for clarity.

Dose et al. have directly measured the kinetics of the interconversion between the two spin states of ferric myoglobin hydroxide using the laser-stimulated Raman temperature-jump technique. For an idealized Fe haem centre of Oh symmetry, the spin-equilibrium is between a low-spin r(A =i) state and a high-spin A(S= ) state ... 

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