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

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 b₅₆₂ (Cyt b₅₆₂) 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 b₅₆₂ 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.