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Thermochromism of heme adducts of Glycera hemoglobin and some other monomeric heme proteins
Journal article   Peer reviewed

Thermochromism of heme adducts of Glycera hemoglobin and some other monomeric heme proteins

Joseph J. Stephanos and Anthony W. Addison
Journal of inorganic biochemistry, v 39(4), pp 351-369
1990
DOI: https://doi.org/10.1016/0162-0134(90)80033-T
PMID: 2167947
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Abstract

Mb, myoglobin Hb m, G. dibranchiata monomeric (light) hemoglobin HMTG, methylthioglycolate, HS.CH 2.CO.OCH 3 LMCT, ligand-to-metal charge-transfer ESR, electron spin (paramagnetic) resonance Cyt-P450, cytochrome P-450 Cytc, Cytochrome- c Hb m(III), Hb m in the met state, in the absence of exogenous ligand G, Gauss (1 G = 10 −4 Tesla) Hb A, hemoglobin-A
The thermally induced difference spectra of myoglobin (Mb) and Glycera dibranchiata hemoglobin (Hb m) derivatives and of cytochrome- c were recorded between 4° and 30°C in the 390–750 nm range. Thermodynamic parameters were estimated and upper and lower temperature limiting spectra were deduced for the various heme protein derivatives' equilibria. The effective iron d-electron population divides the hemes broadly into two different groups of behavior type. In the first group, Hb m(III)N 3, Hb m(III), Mb(III)(H 2O), and Cytc(III) show equilibria between two spin states. The weakest coupling between the heme and the globin occurs among the second group, for Hb m(II)CO and Mb(II)CO, which in the higher temperature limit undergoes averaging of the carbonyl tilt, while an axially elongated geometry is probably accessed for Hb m(II)NO and Mb(II) NO. Examples of the less common situation of increased absorption intensity and/or low-spin states at higher temperature were found in both groups. In the case of the methyl thioglycolate low-spin adducts of Hb m (III), an acid/base equilibrium involviong thioglycolate deprotonation occurs. Apparent enthalpy-entropy compensation is exhibited by all these heme derivatives, and it is suggested that the ΔH° and ΔS° values relate to the intimacy of coupling between the heme structure and the solvent-dependent microconformation of the globin.

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Web of Science research areas
Biochemistry & Molecular Biology
Chemistry, Inorganic & Nuclear
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