Hemoproteins stability

Stability of Oxycomplex. The oxycomplex of various peroxidases and other hemoproteins shows dramatic difference in stability, or the rate of... 

Infrared spectroscopy is one of the most powerful tools for functional studies of hemoproteins reactive to external hgands with infared absorptions in the triple bond region (1900-2200 cm ) where the background level due to absorptions of proteins and water molecules is quite low as described above. However, recent improvement in the sensitivity and stability of the FTIR apparatus with an MCT detector has enabled infrared spectroscopic examination of the protein moiety also. In fact, one of the most sensitive methods for monitoring the dissociation of a COOH group is infrared spectroscopy. 

In this context, the control of O2 affinity by the distal environment of the heme group in hemoproteins can be probed by comparison of wild-type compounds with mutants which do not contain distal histidine [105]. Replacement of distal histidine by glycine results in a 10-fold decrease in O2 affinity. Within the hemoproteins themselves, the lack of distal histidine in aplysia myoblobin compared to horse myoglobin increases the dissociation rate constant by a factor of six, whereas the association rate constants are identical for both systems. The data are again consistent with the stabilization of bound O2 via hydrogen-bonding in horse myoglobin. 

Substituents in the porphyrin ring systems may confer stability and selectivity toward oxidation these attributes are fundamental to the development of efficient model systems mimicking hemoprotein activities. Metalloporphyrins are very vulnerable to destructive oxidation of the porphyrin ligand under strongly oxidizing conditions. Thus, Groves et al. 

Gerothanassis, I. R, Momenteau, M., Loock, B. (1989). Hydrogen-bond stabilization of dioxygen, conformation excitation, and autoxidation mechanism in hemoprotein models as revealed by 0 NMR spectroscopy, J. Am. Chem. Soc., Ill 7006. 

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