Synthesis and Physical Characterization of Novel Heme-Based Model Systems for Photoinitiated Electron Transfer. 1. Complexation of a RuProHis Bifunctional Peptide and Microperoxidase-11

Abstract

This paper describes the synthesis and initial physical characterization of a new type of model system for the investigation of photoinitiated electron transfer (ET) in proteins and polypeptides. This system is based upon a derivative of a heme-containing digestion product of cytochrome c, microperoxidase-11 (MP-11). The vacant axial position of the five-coordinate heme of MP-11 is coordinated to the terminal histidine of a dipeptide having a photoactive ruthenium tris(bipyridine) moiety at its other end (RuProHis). Photoexcitation of the ruthenium group results in rapid (kET > 10 7 s -1 ), reversible ET to the ferric heme. The equilibrium properties of MP-11 and the MP-11/Ru(peptide) complex were characterized with optical absorption, luminescence, and resonance Raman (RR) spectroscopies. Molecular modeling was also employed to examine the structure and energetics of the equilibrium species. Clear evidence for reversible photoinduced ET was observed in time-resolved luminescence and transient resonance Raman studies of the MP-11/RuProHis samples.