Reduction potentials hemoglobin

The most important and universal type of chemical equilibria to which a heme protein is subjected in natural environments is pH equilibria, involving the protein aminoacid residues and the ionizable groups of the porphyrin, the propionate side chains. Beside the effects on the overall protein structure, which are outside the scope of this review, the major consequences of proton equilibria may be the changes of the heme reduction potential (electron affinity), called the redox-Bohr effect (see Sect. 3.2), by analogy to the pH effect on the oxygen affinity of hemoglobin (Bohr effect). 

Oxidation-reduction potentials are expressed in volts relative to the standard hydrogen electrode at 0 volts, and represent the tendency of a compound to lose electrons (oxidation) or gain electrons (reduction). Various enzyme systems in respiration reactions (e.g., the cytochromes) utilizing ascorbic acid, hemoglobin, as well as reactions in the Krebs cycle (succinic and fumaric acids) involve electron transfers. Drugs can affect all these systems, and the consequences must be taken into account. 

The kinetics of the reduction of hemoglobin by Fe(III) and Cu(II) complexes indicate the presence of both simple outer-sphere and site-specific electron transfer mechanisms. With the Fe(III) chelate oxidants the pathway is dependent on the reduction potential and the stability of the Hb complex, while for Cu(II) oxidations the outer-sphere process occurs at the a subunits, with the site-specific mechanism involving metal binding at the Cys p-93 residue. 

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