The membrane-bound C type cytochromes and the interaction between the downhill and uphill electron transfer pathways in the acidophilic chemolitotrophic ferrous ion-oxidizing bacterium Thiobacillus ferrooxidans

摘要

T. ferrooxidans contains three membrane bound cytochrome c with apparent molecular masses of 46,30 and 23 kDa. No significant homologies to other cytochromes were detected in data banks for the monohemic 46 kDa cytochrome (C_x) which we found to be an integral membrane protein. The 23 kDa cytochrome c has been purified and characterized: it is a c_4 type cytochrome firmly attached to the membrane. The 30 kDa cytochrome has been previously suggested to be of the C_1 type. The bc_1 and cytochrome oxidase complexes have been partially purified. Characterization of the oxidase complex clearly showed, for the first time, that this oxidase was of the aa_3 type despite the α peak of its reduced form at 597 nm. In other respects, the results of purification have shown the existence of a strong interaction between this oxidase and cytochrome c_x. Based on these results, a model is presented which suggests a positioning of the c type cytochromes in order to connect the uphill and downhill electron transfer pathways. 'Present address: Department of Medicine and Cancer Center, University of California, San Diego, La Jolla, CA 92093-0688.