The Bc(1) Complex of Rhodobacter Sphaeroides and Its Integration Into the Photosynthetic Chain

Abstract

165 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1998.In this thesis, the effects of two inhibitors, funiculosin and zinc, on the bc\sb1 complex of Rhodobacter sphaeroides, and the role of isocyt c\sb2 in the photosynthetic chain were studied. Also the organization of the photosynthetic electron transfer chain of Rb. sphaeroides and the role of PufX were investigated. In Rb. sphaeroides, a bulky Val residue at position 209 in the bc\sb1 complex has been shown to provide the resistance to funiculosin. The mutation of Val209 to the smaller Ala allows funiculosin binding at the Q\sb0-site, and the additional change of Ile213 to Leu potentiates this effect. The effects of funiculosin on the Q\sb0-site of the bc\sb1 complex in the mutant strains suggest that changes in structural packing close to the Q\rm\sb{i}-site exert a relatively long-range secondary effect. Zinc inhibits the bc\sb1, complex of Rb. sphaeroids by binding a single inhibition site at the Q\sb0-site. But, when the bc\sb1, complex is embedded in the membrane, it is shielded from the inhibitory effect of zinc by the presence phospholipids in membranes, which interact with zinc ions, and compete effectively until the binding site are saturated. Isocyt c\sb2 has been shown to replace cyt c\sb2, and allow the system to undergo rapid electron transfer with kinetics similar to wild type in spite of its low concentration in cells and chromatophores, suggesting rapid diffusion of isocyt c\sb2,between several chains. Structural models of PufX suggest that it forms a dimer, providing a gate in LH1. The kinetic data also suggest two permeation pathways of quinone through the LH1; one using PufX and another less efficient pathway that depends on disorder in the LH1 palisade. Two models for the organization of photosynthetic electron transfer chain in Rb. sphaeroides, supercomplex model and heterogeneity model were examined with wild type and overproducer strains of Rb. sphaeroides. No fixed stoichiometry of photosynthetic components, and the dependence of the equilibrium constants on the light intensity and the type of inhibitors were explained more simply with the heterogeneity model rather than supercomplex model. The heterogeneity model was also consistent with the data suggesting a role for PufX.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD