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 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: kCS = 320–600 s−1) and subsequent charge recombination (CR: kCR = 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. Photoinduced electron transfer was observed in artificial cytochrome b562 co-assemblies and heterodimers containing Fe and Zn porphyrins as cofactors. The kinetic constants of the electron transfer are strongly dependent on the hydrogen-bond interactions occurring at the protein interfaces. A kinetics analysis using Marcus theory supports the single-step electron transfer. [Display omitted] •Cytochrome b562 co-assemblies/heterodimers with Fe and Zn porphyrins were prepared.•Photoinduced electron transfer was monitored in the co-assemblies and heterodimers.•The kinetics of the electron transfer strongly depends on the hydrogen bond network.•The position of cofactors in the heterodimer affects the electron transfer kinetics.•Marcus equation suggests a single-step electron transfer in the present systems.