Cytochrome interaction with redox partners

Purdy M. M. Koo L. S. Ortiz de Montellano P. R. Klinman J. P. Steady-state kinetic investigation of cytochrome P450cam interaction with redox partners and reaction with molecular oxygen. Biochemistry 2004, 43, 271-281. 

The involvement of the lysine residues has been explored. Thus, trifluoroacetylation of lysine residues 13, 55 and 99 has been carried out,662 but only modification of residue 13 affects the reaction with cytochrome oxidase. Modification of lysine residues 13, 25, 27, 72 and 79 decreased the reaction rate of cytochrome c with cytochrome bs. It is possible that the lysine groups in unmodified cytochrome c interact with the carboxylate groups in cytochrome b5 (Asp-48, Glu-43, Glu-44 and Asp-60) and one of the heme propionate groups.663 In general, such studies support the proposal that these lysine groups represent binding sites for redox partners of cytochrome c. 

Many of the reactions of the plastocyanins and azurins with other redox proteins follow Marcus behaviour.946 These reactions all show a single mechanism of electron transfer, with no kinetic selectivity and no specific interactions between the proteins. The notable exception to this behaviour is cytochrome / (c552), where a specific interaction occurs,934 appropriate for its natural redox partner. Equation (48) represents a probable sequence of electron carriers, although it is difficult to extrapolate conclusions to the membrane-bound proteins. 

Domains on cytochrome c for interaction with physiological redox partners. The heme edge is represented by the shaded rectangle. The number of circles around a given Lys residue is proportional to the percentage of the observed inhibition in redox assays when the corresponding CDNP-modified cytochrome c is used. 

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