A cytochrome cc'-like haemoprotein isolated from Azotobacter vinelandii

Spectroscopic characterization of nitrosylheme in nitric oxide complexes of ferric and ferrous cytochrome c' from photosynthetic bacteria

Reactions of ferric and ferrous cytochromes c' from four photosynthetic bacteria (Rhodobacter capsulatus ATCC 11166, Rhodopseudomonas palustris ATCC 17001, Rhodospirillum rubrum ATCC 11170, and Chromatium vinosum ATCC 17899) with nitric oxide have been investigated by electronic absorption and electron paramagnetic resonance spectroscopies. The heme iron(III) of these ferric cytochromes c' has been recently reported to be in a quantum mechanically admixed (S = 5/2, 3/2) state [Fujii, S., Yoshimura, T., Kamada, H., Yamaguchi, K., Suzuki, S., Shidara, S. and Takakuwa, S. (1995) Biochim. Biophys. Acta 1251, 161-169]. The affinity of ferric cytochromes c' for NO among these bacterial species (C. vinosum > Rps. palustris approximately Rb. capsulatus >> R. rubrum) was apparently related to the S = 3/2 content in the or der. In the reaction of ferrous cytochrome c' with NO, six- and five-coordinated nitrosylhemes, which represent species with and without a ligand at the axial position trans to nitrosyl group, have been formed. The content of six-coordinated nitrosylheme in NO-ferrous cytochrome c' has been determined to be Rb. capsulatus approximately Rps. palustris > C. vinosum < R rubrum, suggesting that a stability of iron-to-histidine bond decreases with this order. The NO reactions of ferric and ferrous cytochromes c' from photosynthetic bacteria have been compared with those of cytochromes c' from denitrifying bacteria.

Electron paramagnetic resonance studies of ferric cytochrome c' from photosynthetic bacteria

Electronic ground nature of ferric cytochromes c' isolated from five photosynthetic bacteria. Chromatium vinosum ATCC 17899, Rhodobacter capsulatus ATCC 11166, Rhodopseudomonas palustris ATCC 17001, Rhodospirillum molischianum ATCC 14031, and Rhodospirillum rubrum ATCC 11170 has been investigated by electron paramagnetic resonance (EPR) spectroscopy. EPR spectra indicate that the electronic ground state of five ferric cytochromes c' is a quantum mechanical admixed-spin state of a high spin (S = 5/2) and an intermediate spin (S = 3/2) at pH 7.2 and is high-spin state at pH 11.0. At physiological pH, however, the content of an intermediate spin state differs with the bacterial source of the protein: approximately 50%, Chromatium vinosum; approximately 40%, Rhodobacter capsulatus and Rhodopseudomonas palustris; approximately 10%, Rhodospirillum molischianum and Rhodospirillum rubrum. Computer simulation of the spectra supports this diversity of the contribution of an intermediate spin state. Model studies of the ferric porphyrin complexes suggest that the correlation between content of an intermediate spin state and heme iron displacement from the mean heme plane. Therefore, the variation of the content of an intermediate spin state observed in the present study reflects the subtle difference in the degree of heme iron displacement among the proteins.

Cytochrome c' of Paracoccus denitrificans

Cytochrome c' was identified in periplasmic extracts of the Paracoccus denitrificans strains LMD 22.21 and LMD 52.44. The cytochrome c' was purified from the latter using the device of sequential molecular exclusion chromatography in the dimeric and monomeric states. Although showing the overall spectroscopic features of the cytochrome c' family, the Paracoccus cytochrome c' is unusual in having a red-shifted oxidised Soret band at 407 nm. Also unusual is the midpoint potential of 202 mV, well above the known cytochrome c' range. The amino-acid composition of Pa. denitrificans cytochrome c' showed the high alanine and low proline content characteristic of the group and reflecting the predominantly alpha-helical character of the protein. Comparison of the amino-acid compositions suggests some similarity to the cytochromes c' of Chromatium vinosum and halotolerant Paracoccus.

Spectral properties of nitric oxide complex of cytochrome c' from Rhodopseudomonas capsulata B100

The spectral properties for NO complexes of ferric and ferrous cytochrome c' from photosynthetic bacterium Rhodopseudomonas capsulata B100 are reported. The electronic absorption, MCD, and EPR spectra have been compared with those of the NO complexes of the other cytochromes c' and horse heart cytochrome c. The NO-ferrous cytochrome c' would be a mixture of NO complexes with six- and five-coordinate nitrosylheme, suggesting that the heme-iron to histidine bond in the ferrous cytochrome c' is more stable than that from chemoheterotrophic bacteria. The reaction product of ferric cytochrome c' with NO exhibited the spectra similar to NO-ferric derivatives of the other hemoproteins, which indicates the formation of NO-ferric cytochrome c'.

Amino acid sequences of bacterial cytochromes c' and c-556

The cytochrome c' are electron transport proteins widely distributed in photosynthetic and aerobic bacteria. We report the amino acid sequences of the proteins from 12 different bacterial species, and we show by sequences that the cytochromes c-556 from 2 different bacteria are structurally related to the cytochromes c'. Unlike the mitochondrial cytochromes c, the heme binding site in the cytochromes c' and c-556 is near the COOH terminus. The cytochromes c-556 probably have a methionine sixth heme ligand located near the NH2 terminus, whereas the cytochromes c' may be pentacoordinate. Quantitative comparison of cytochrome c' and c-556 sequences indicates a relatively low 28% average identity.

Respiratory properties of cytochrome-c-deficient mutants of Azotobacter vinelandii

Cytochrome-c-deficient mutants of Azotobacter vinelandii have been isolated following mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. These mutants grow well under nitrogen-fixing conditions and studies of the physiology and energy conservation efficiency show no apparent differences from those of the parent strain. Under oxygen-limited growth conditions, the growth rate of the cytochrome-c-deficient mutant was slightly slower (approx. 15%) than that of the parent strain. Cytochromes of the c-type are required for the oxidation of artificial electron donors such as reduced N,N,N',N'-tetramethyl-p-phenylenediamine [Ph(NMe2)2]. This study could not demonstrate a physiological role for the c-type cytochromes which supports the idea that the minor Ph(NMe2)2-oxidizing pathway of the electron transport chain may be independent of the major pathway terminated by cytochrome d.

Cytochromes c-556 from three genetic races of Agrobacterium. Purification and comparison of their properties

1. The soluble cytochromes c-556 from three strains of Agrobacterium tumefaciens, B6, II Chrys and Apple 185 have been purified to homogeneity. The strains are representative members of the three main genetic races of Agrobacterium. The purity of the final preparations was established by electrophoresis with an without sodium dodecyl sulphate, by analytical isoelectric focusing and ultracentrifugation, and by N-terminal analysis. 2. Properties of these cytochromes were compared wih those of cytochrome c-556 from A. tumefaciens, strain B2a, a member of the same genetic race as strain B6. The four cytochromes are monohaem proteins with molecular weights of about 12300 (determined by four different methods). The isoelectric points of those from strains B6 and B2a are identical at pH 5.5, but they differ from the cytochromes of the other genetic races: cytochrome c-556 from strain Apple 185 is more acidic (ph 5.2) and that from strain II Chrys more basic (pH 6.2). The cytochromes from strains b6 and B2a have very similar but not identical amino acid compositions; both of them differ more from Apple 185 than from II Chrys c-556. 3. Comparison of the tryptic, chymotryptic and thermolytic fingerprints of cytochrome c-556 from strains B2a and II Chrys reveals strong homology between the primary structures of these cytochromes. Therefore and because of the sequence identity of the first eight residues, the cytochromes c-556 from strains II Chrys, B6 and B2a are most likely C-terminal haem-bound, of the same type as the cytochrome c' from photosynthetic bacteria.

The oxidation-reduction potentials of cytochrome o + c4 and cytochrome o purified from Azotobacter vinelandii

Oxidation-reduction titrations of Azotobacter vinelandii cytochrome o + c4 and cytochrome o were performed with simultaneous potential and absorbance measurements under anaerobic conditions. Cytochrome c4 has a midpoint potential (Em, 7.4) of 260mV and purified cytochrome o has an Em, 7.4 of -18mV. Little change in the midpoint potential of cytochrome o was observed when titrated in the pH range 6.2--9.8.