Photoinduced electron transfer within supramolecular hemoprotein co-assemblies and heterodimers containing Fe and Zn porphyrins

Electron transfer (ET) events occurring within metalloprotein complexes are among the most important classes of reactions in biological systems. This report describes a photoinduced electron transfer between Zn porphyrin and Fe porphyrin within a supramolecular cytochrome b(562) (Cyt b(562)) co-assembly or heterodimer with a well-defined rigid structure formed by a metalloporphyrin-heme pocket interaction and a hydrogen-bond network at the protein interface. The photoinduced charge separation (CS: k(CS) = 320-600 s(-1)) and subsequent charge recombination (CR: k(CR) = 580-930 s(-1)) were observed in both the Cyt b(562) co-assembly and the heterodimer. In contrast, interestingly, no ET events were observed in a system comprised of a flexible and structurally-undefined co-assembly and heterodimers which lack the key hydrogen-bond interaction at the protein interface. Moreover, analysis of the kinetic constants of CS and CR of the heterodimer using the Marcus equation suggests that a single-step ET reaction occurs in the system. These findings provide strong support that the rigid hemoprotein-assembling system containing an appropriate hydrogen-bond network at the protein interface is essential for monitoring the ET reaction.