The specific aim of the proposed research is to characterize the structural and electronic properties of the active pigments in energy transducing proteins. The bacterial photosynthetic reaction center (RC) has been chosen for study because this class of proteins represents a prototypical model system for investigating the properties that facilitate fast electron transfer over distances on the order of the width of the biological membrane. In addition, the RC is the only integral membrane protein for which the macromolecular arrangement of the active pigments in the protein matrix is known. The principal investigative tool that will be used is resonance Raman (RR) spectroscopy. The first objective is to characterize the UV-vis-excitation (ca. 350-700 nm) RR spectra of the bacterochlorphyll (BChl) and bacteriopheophytin (BPh) pigments is RCs from Rb. sphaeroides, Rb. capsulatus and Rps. viridis wild-type. The goal of these studies is to examine the individual BChl and BPh molecules with as much selectivity as possible in order to assess the structural similarities and/or differences between the various pigments in RCs from a given species and between RCs from different species. The second objective is to characterize the UV- vis-excitation RR spectra of a number of genetically modified RCs from Rb. capsulatus. These studies will focus on systems in which genetic modifications have been made in the amino acid residues in the vicinity of the primary electron donor and acceptor and also the accessory BChls. These studies will be conducted in parallel with those on the wild-type systems in order to assess the structural consequences of the various site- specific mutations. The third objective is to probe the red-most, Qy absorptions (ca. 750-1000 nm) of the BChls and BPhs by using RR techniques. The red-most band of the primary donor (ca. 850-1000 nm) will be the focal point of the near-infrared (NIR) RR studies. The goal of these studies is to characterize the vibrational and electronic properties of the lowest- energy electronic states. The fourth objective is to obtain NIR-excitation RR spectra of RCs in which genetical modifications have been made in the vicinity of the photophysically active pigments. The goal of these studies is to determine how modifications in specific amino acids influence the vibrational and electronic properties of the electron-donating excited state of RCs.
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