Isolation and characterization of cytochrome C1 from photosynthetic bacterium Rhodopseudomonas sphaeroides R-26

Characterization of purified cytochrome c1 from Rhodobacter sphaeroides R-26

Cytochrome c1 from a photosynthetic bacterium Rhodobacter sphaeroides R-26 has been purified to homogeneity. The purified protein contains 30 nmol heme per mg protein, has an isoelectric point of 5.7, and is soluble in aqueous solution in the absence of detergents. The apparent molecular weight of this protein is about 150,000, determined by Bio Gel A-0.5 m column chromatography; a minimum molecular weight of 30,000 is obtained by sodium dodecylsulfate polyacrylamide gel electrophoresis. The absorption spectrum of this cytochrome is similar to that of mammalian cytochrome c1, but the amino acid composition and circular dichroism spectral characteristics are different. The heme moiety of cytochrome c1 is more exposed than is that of mammalian cytochrome c1, but less exposed than that of cytochrome c2. Ferricytochrome c1 undergoes photoreduction upon illumination with light under anaerobic conditions. Such photoreduction is completely abolished when p-chloromercuriphenylsulfonate is added to ferricytochrome c1, suggesting that the sulfhydryl groups of cytochrome c1 are the electron donors for photoreduction. Purified cytochrome c1 contains 3 +/- 0.1 mol of the p-chloromercuriphenylsulfonate titratable sulfhydryl groups per mol of protein. In contrast to mammalian cytochrome c1, the bacterial protein does not form a stable complex with cytochrome c2 or with mammalian cytochrome c at low ionic strength. Electron transfer between bacterial ferrocytochrome c1 and bacterial ferricytochrome c2, and between bacterial ferrocytochrome c1 and mammalian ferricytochrome c proceeds rapidly with equilibrium constants of 49 and 3.5, respectively. The midpoint potential of purified cytochrome c1 is calculated to be 228 mV, which is identical to that of mammalian cytochrome c1.

The EPR spectra of the cytochrome b-c1 complex of Rhodopseudomonas sphaeroides

The purified cytochrome b-c1 complex of Rhodopseudomonas sphaeroides has two b cytochromes distinguishable by optical, thermodynamic and electron paramagnetic resonance criteria (gz values are approximately equal to 3.75 and approximately equal to 3.4). EPR features typical of a Rieske iron sulfur cluster (g values of 2.03 1.90 and 1.81) and a c1 type cytochrome (g approximately equal to 3.4) were also observed. The b and c1 cytochromes were individually purified from the complex. The cytochrome c1 retained its native EPR spectrum. The b cytochrome lost over 90% of the intensity from the 'b566 type' heme site (g approximately equal to 3.75), while the 'b561 type' heme site (g approximately equal to 3.4) retained its native EPR spectrum.

Soluble cytochrome composition of the purple phototrophic bacterium, Rhodopseudomonas sphaeroides ATCC 17023

A detailed study of the soluble cytochrome composition of Rhodopseudomonas sphaeroides (ATCC 17023) indicates that there are five c-type cytochromes and one b-type cytochrome present. The molecular weights, heme contents, amino acid compositions, isoelectric points, and oxidation-reduction potentials were determined and the proteins were compared with those from other bacterial sources. Cytochromes c2 and c' have previously been well characterized. Cytochrome c-551.5 is a diheme protein which has a very low redox potential, similar to certain purple bacterial and algal cytochromes. Cytochrome c-554 is an oligomer, which is spectrally similar to the low-spin isozyme of cytochrome c' found in other purple bacteria (e.g., Rhodopseudomonas palustris cytochrome c-556). An unusual high-spin c-type heme protein has also been isolated. It is spectrally distinguishable from cytochrome c' and binds a variety of heme ligands including oxygen. A large molecular-weight cytochrome b-558 is also present which appears related to a similar protein from Rhodospirillum rubrum, and the bacterioferritin from Escherichia coli. None of the soluble proteins appear to be related to the abundant membrane-bound c-type cytochrome in Rps. sphaeroides which has a larger subunit molecular weight similar to mitochondrial cytochrome c1 and chloroplast cytochrome f.

The major soluble cytochromes of the obligately aerobic sulfur bacterium, Thiobacillus neapolitanus

Four cytochromes were isolated from soluble extracts of the aerobic sulfur bacterium, Thiobacillus neapolitanus. The two most abundant proteins were purified to homogeneity and thoroughly characterized. Cytochrome c-554 (547) is a monomeric, small molecular weight protein which is unusual in having two well-resolved alpha peaks in UV-visible absorption spectra. The redox potential is 208 mV. Native cytochrome c-549 is oligomeric, but has a subunit size of about 26,000. The yield of this protein could be improved dramatically by washing membranes with 30% ammonium sulfate, but the material solubilized by this method had a larger native molecular weight than that in the initial 0.1 M Tris-Cl extract and behaved differently on chromatography. The properties of cytochrome c-549 including subunit size and UV-visible absorption spectra are similar to mitochondrial cytochrome c1 and chloroplast cytochrome f, which suggests that it may be a modified form of the predominant membrane cytochrome. Based on cytochrome content, it is suggested that T. neapolitanus is not closely related to other thiobacilli.

Purification and properties of cytochrome b from photosynthetic bacterium Rhodopseudomonas sphaeroides R-26

Cytochrome b of R. sphaeroides R-26 has been purified from the isolated cytochrome b-c1 complex to homogeneity. The purification procedure involves Triton X-100 and urea solubilization, calcium phosphate column chromatography at different pH values, and ammonium sulfate fractionation. The purified protein contains 23 nmol heme per mg protein and has an apparent molecular weight of 43,000, as determined by sodium dodecylsulfate polyacrylamide gel electrophoresis. The spectral characteristics of purified cytochrome b are similar to those of cytochrome b in the active cytochrome b-c1 complex but with a lower absorbance. The amino acid composition has been determined and compared with cytochrome b purified from other sources.