Membrane-Associated C-Type Cytochromes of Rhodobacter Capsulatus Involved in Photosynthesis and Respiration
Purple nonsulfur facultative phototrophs, e.g. Rhodobacterspecies (Rhodobacter capsulatusand Rhodobacter sphaeroides) provide excellent model systems for studying the structure, function, regulation and biogenesis of cytochrome (cyt) complexes involved in photosynthesis (Ps) and respiration (Res). In these species Ps electron transport pathway is cyclic. It involves the photochemical reaction center (RC) and the ubihydroquinone: cyt coxidoreductase (also called the cyt bc 1 complex) connected to each other by c-type cyts and the ubihydroquinone (UQ) pool (Figure 1). On the other hand, the Res pathways are often branched at the UQ pool and contain several terminal oxidases thought to work at different oxygen tensions. R. capsulatushas a quinol oxidase (Qox) and a cyt coxidase (Cox) of cbb 3 -typewhile R. sphaeroidesalso has an additional cyt coxidase of aa 3-ty?e (Figure 1). These electron transport components are involved in production of energy which is essential for cell survival. They are responsible for translocation of protons across the cellular membrane to produce a proton gradient which is then used for ATP synthesis. Because of their crucial importance for life they are often multiplicated with overlapping roles, so that the absence of any one of them, although restrictive under some growth modes, is rarely lethal for the organism. Most of the energy transduction complexes contain c-type cyts which are attached to the cytoplasmic membrane with their co-valently bound heme groups facing the periplasm.
KeywordsTyrosine Respiration Carboxyl Proline Photosynthesis
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