Respiratory proteins from the extremely thermophilic aerobic bacterium, Thermus thermophilus. Purification procedures for cytochromes c552, c555,549, and c1aa3 and chemical evidence for a single subunit cytochrome aa3.

We have developed a chemically defined, minimal growth medium for Thermus thermophilus which is suitable for nutritional studies, isotopic enrichment, and genetic manipulation of the organism. Reliable procedures are described for the large scale purification of cytochrome c552 from the periplasm and for cytochrome c555,549 and cytochrome c1 aa3 from the plasma membrane. In contrast to a previous report (Fee, J. A., Choc, M. G., Findling, K. L., Lorence, R., and Yoshida, T. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 147-151) which suggested a molecular weight near 200,000, the cytochrome c1aa3 complex was shown by protein and amino acid analyses to have Mr approximately 93,000. Sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis and reversed phase high performance liquid chromatography, combined with amino acid analyses, revealed the presence of only two proteins in a 1:1 ratio: C-protein has Mr approximately 33,000, binds heme C, and is thought to correspond to cytochrome c1. A-protein has Mr approximately 55,000 and is thought to bind the four redox components (2 heme A and 2 Cu) of cytochrome aa3.

Purification and characterization of the Rieske iron-sulfur protein from Thermus thermophilus. Evidence for a [2Fe-2S] cluster having non-cysteine ligands.

We have purified the Rieske iron-sulfur protein from Thermus thermophilus. Chemical analyses show that the protein contains iron, labile sulfide, and cysteine in equimolar concentrations, four of each for Mr approximately 20,000. The oxidized and reduced form of the protein have been characterized by optical, EPR, CD, magnetic CD and Mössbauer spectroscopies. Our data suggest the presence of a unique iron-sulfur center. Mössbauer studies of the oxidized and reduced protein demonstrate unambiguously that the protein contains clusters with [2Fe-2S] cores. The iron analyses and the Mössbauer data, taken together, suggest that the protein has two [2Fe-2S] clusters. This is supported by the observation that two electrons are required for complete reduction of the protein and that the g = 1.94-type signal of the reduced protein has a spin concentration of one spin (S = 1/2) per 2Fe. Within the excellent resolution of the Mössbauer and EPR data, the two clusters are identical. Our results thus suggest that each [2Fe-2S] cluster is coordinated by at most two cysteine residues. The Mössbauer spectra of the reduced protein were analyzed with an S = 1/2 spin Hamiltonian. The hyperfine parameters obtained are very similar to those reported for putidaredoxin. The main difference is that the Rieske protein exhibits an increased isomer shift at the Fe2+ site, suggesting that non-cysteine ligands are coordinated to the site that becomes reduced to Fe2+ upon reduction. A comparison of our data with those reported for various NADH-dependent dioxygenases suggest that these enzymes contain a Rieske-type [2Fe-2S] center.

Mössbauer study of a bacterial cytochrome oxidase: cytochrome c1aa3 from Thermus thermophilus.

Cytochrome c1aa3 from Thermus thermophilus has optical and EPR properties similar to bovine cytochrome c oxidase. We have studied 87Fe-enriched samples with Mössbauer spectroscopy in the fully oxidized and fully reduced states and in the oxidized state complexed with cyanide. The cytochromes a and c1 yielded spectra quite similar to those reported for the cytochromes c and b5; in the oxidized state the spectra reflect noninteracting, low spin ferric hemes, whereas the a- and c1-sites of the reduced enzyme are typical of low spin ferrous hemochromes. The spectra of the reduced enzyme show that reduced cytochrome a3 is high spin ferrous, with Mössbauer parameters quite similar to those of deoxymyoglobin. Upon addition of cyanide to the oxidized enzyme, the a3-site exhibits in the absence of an applied magnetic field and at temperatures down to 1.3 K a quadrupole doublet with parameters typical of low spin ferric heme-CN complexes. The low temperature spectra taken in applied magnetic fields show that the electronic ground state of the a3-CN complex has integer electronic spin, suggesting ferromagnetic coupling of the low spin ferric heme (S = 1/2) to Cu2+ (S = 1/2) to yield as S = 1 ground state. We have examined the oxidized enzyme from two different preparations. Both had good activity and identical optical and EPR spectra. The Mössbauer spectra, however, revealed that the a3-site had a substantially different electronic structure in the two preparations. Neither configuration had properties in accord with the widely accepted spin-coupling model proposed for the bovine enzyme.

Properties of a copper-containing cytochrome c1aa3 complex: a terminal oxidase of the extreme thermophile Thermus thermophilus HB8.

From the plasma membrane of Thermus thermophilus HB8 we have partially purified a detergent-solubilized complex of cytochromes a and c1 that actively catalyzes the transfer of electrons from ascorbate via a redox dye to oxygen. The complex is composed of two types of polypeptides, with molecular weights of approximately 55,000 and 33,000. Quantitative analysis revealed the presence of heme a, heme c, and copper in a ratio of 2:1:2, with the heme a being present at 10 +/- 1.3 nmol/mg of protein. The heme c was shown to be associated with the molecular weight 33,000 peptide and is suggested to be of the c1 type. The optical and electron paramagnetic resonance properties of this complex were found to be similar to those of eukaryotic cytochrome oxidase, suggesting the following arrangement of chromophores: a magnetically isolated cytochrome c1 and an oxygen-reducing functional unit consisting of two heme a groups and two copper ions associated with one or more larger peptides.