Hemoproteins structural differences

Fig. 3 illustrates schematically the structures of some well characterized hemoproteins. In the cytochrome series the desired range of redox potentials is achieved by variations in the axial ligands, contributed by the porphyrin moiety, as well as by substitutions around the periphery of the tetrapyrrole nucleus with groups of differing electron-attracting ability. 

A comparison of porphyrin and pincer activity rationalized through reactivity index Porphyrin and pincer complexes are both important categories of compounds in biological and catalytic systems. Structure, spectroscopy, and reactivity properties of porphyrin pincers are systematically studied for selection of divalent metal ions. It is reported that the porphyrin pincers are structurally and spectroscopically different from their precursors and are more reactive in electrophilic and nucleophilic reactions. These results are implicative in chemical modification of hemoproteins and understanding the chemical reactivity in heme-containing and other biologically important complexes and cofactors [45]. 

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