Interaction of horse cytochrome c with the photosynthetic reaction center of Rhodospirillum rubrum.
Mitochondrial cytochrome c (horse), which is a very efficient electron donor to bacterial photosynthetic reaction centers in vitro, binds to the reaction center of Rhodospirillum rubrum with an approximate dissociation constant of 0.3-0.5 microM at pH 8.2 and low ionic strength. The binding site for the reaction center is on the frontside of cytochrome c which is the side with the exposed heme edge, as revealed by differential chemical acetylation of lysines of free and reaction-center-bound cytochrome c. In contrast, bacterial cytochrome c2 was found previously to bind to the detergent-solubilized reaction center through its backside, i.e., the side opposite to the heme cleft [Rieder, R., Wiemken, V., Bachofen, R., and Bosshard, H. R. (1985). Biochem. Biophys. Res. Commun. 128, 120-126]. Binding of mitochondrial cytochrome c but not of mitochondrial cytochrome c2 is strongly inhibited by low concentrations of poly-L-lysine. The results are difficult to reconcile with the existence of an electron transfer site on the backside of cytochrome c2.
D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D006736:Horses; D007700:Kinetics; D045322:Photosynthetic Reaction Center Complex Proteins; D011485:Protein Binding; D012247:Rhodospirillum rubrum / Q000378:metabolism*
D001426:Bacterial Proteins; D003574:Cytochrome c Group; D045322:Photosynthetic Reaction Center Complex Proteins