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

Affiliation

Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan; Frontier Research Base for Global Young Researchers, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan; PRESTO, Japan Science and Technology Agency (JST), Kawaguchi 332-0012, Japan. Electronic address: [Email]

Abstract

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.

Keywords

Cytochrome b(562),Hemoprotein assembly,Hydrogen bond network,Marcus theory,Photoinduced electron transfer,

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