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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cytochrome c(6) donates electrons to photosystem I (PS I) in Synechococcus sp. PCC 7002. In this work, we provide evidence for rapid electron transfer (t(1/2) = 3 micros) from cytochrome c(6) to PS I in this cyanobacterium in vivo, indicating prefixation of the reduced donor protein to the photosystem. We have investigated the cytochrome c(6)-PS I interaction by laser flash-induced spectroscopy of intact and broken cells and by redox titrations of membrane and supernatant fractions. Redox studies revealed the expected membrane-bound cytochrome f, b(6), and b(559) species and two soluble cytochromes with alpha-band absorption peaks of 551 and 553 nm and midpoint potentials of -100 and 370 mV, respectively. The characteristics and the symmetrical alpha-band spectrum of the latter correspond to typical cyanobacterial cytochrome c(6) proteins. Rapid oxidation of cytochrome c(6) by PS I in vivo results in a unique, asymmetric oxidation spectrum, which differs significantly from the spectra obtained for cytochrome c(6) in solution. The basis for the unusual cytochrome c(6) spectrum and possible mechanisms of cytochrome c(6) fixation to PS I are discussed. The occurrence of rapid electron transfer to PS I in cyanobacteria suggests that this mechanism evolved before the endosymbiotic origin of chloroplasts. Its selective advantage may lie in protection against photo-oxidative damage as shown for Chlamydomonas.
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PMID:Rapid electron transfer to photosystem I and unusual spectral features of cytochrome c(6) in Synechococcus sp. PCC 7002 in vivo. 1152 99

Synechocystis sp. PCC 6803 contains three respiratory terminal oxidases (RTOs): cytochrome c oxidase (Cox), quinol oxidase (Cyd), and alternate RTO (ARTO). Mutants lacking combinations of the RTOs were used to characterize these key enzymes of respiration. Pentachlorophenol and 2-heptyl-4-hydroxy-quinoline-N-oxide inhibited Cyd completely, but had little effect on electron transport to the other RTOs. KCN inhibited all three RTOs but the in vivo K(I) for Cox and Cyd was quite different (7 vs. 27 microM), as was their affinity for oxygen (K(M) 1.0 vs. 0.35 microM). ARTO has a very low respiratory activity. However, when uptake of 3-O-methylglucose, an active H+ co-transport, was used to monitor energization of the cytoplasmic membrane, ARTO was similarly effective as the other RTOs. As removal of the gene for cytochrome c(553) had the same effects as removal of ARTO genes, we propose that the ARTO might be a second Cox. The possible functions, localization and regulation of the RTOs are discussed.
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PMID:Characterization of three bioenergetically active respiratory terminal oxidases in the cyanobacterium Synechocystis sp. strain PCC 6803. 1158 51

A bacterial two-hybrid assay revealed interaction between a protein now designated bacterial Atx1 and amino-terminal domains of copper-transporting ATPases CtaA (cellular import) and PacS (thylakoid import) but not the related zinc (ZiaA) or cobalt (CoaT) transporters from the same organism (Synechocystis PCC 6803). The specificity of metallochaperone interactions coincides with metal specificity. After reconstitution in a N(2) atmosphere, bacterial Atx1 bound 1 mol of copper mol(-1), and apoPacS(N) acquired copper from copper-Atx1. Copper was displaced from Atx1 by p-(hydroxymercuri)phenylsulfonate, indicative of thiol ligands, and two cysteine residues were obligatory for two-hybrid interaction with PacS(N). This organism contains compartments (thylakoids) where the copper proteins plastocyanin and cytochrome oxidase reside. In copper super-supplemented mutants, photooxidation of cytochrome c(6) was greater in Deltaatx1DeltactaA than in DeltactaA, showing that Atx1 contributes to efficient switching from iron in cytochrome c(6) to copper in plastocyanin for photosynthetic electron transport. Cytochrome oxidase activity was also less in membranes purified from low [copper]-grown Deltaatx1 or DeltapacS, compared with wild-type, but the double mutant Deltaatx1DeltapacS was non-additive, consistent with Atx1 acting via PacS. Conversely, activity in Deltaatx1DeltactaA was less than in either respective single mutant, revealing that Atx1 can function without the major copper importer and consistent with a role in recycling endogenous copper.
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PMID:A copper metallochaperone for photosynthesis and respiration reveals metal-specific targets, interaction with an importer, and alternative sites for copper acquisition. 1173 76

Two operons have been cloned from Anabaena sp. strain PCC 7120 DNA, each of which encodes the three core subunits of distinct mitochondrial-type cytochrome c oxidases. The two operons are only 72 to 85% similar to one another at the nucleotide level in the most conserved subunit. One of these, coxBACII, is induced >20-fold in the middle to late stages of heterocyst differentiation. Analysis of green fluorescent protein reporters indicates that this operon is expressed specifically in proheterocysts and heterocysts. The other operon, coxBACI, is induced only 2.5-fold following nitrogen step-down and is expressed in all cells. Surprisingly, a disruption mutant of coxAII, the gene encoding subunit I of the heterocyst-specific oxidase, grows normally in the absence of combined nitrogen. It is likely that coxBACI and/or two other putative terminal oxidases present in the Anabaena sp. strain PCC 7120 genome are able to compensate for the loss of the heterocyst-specific oxidase in providing ATP for nitrogen fixation and maintaining a low oxygen level in heterocysts.
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PMID:Newly identified cytochrome c oxidase operon in the nitrogen-fixing cyanobacterium Anabaena sp. strain PCC 7120 specifically induced in heterocysts. 1194 64

The oxygen-evolving machinery of photosystem II in cyanobacteria is associated with three extrinsic proteins: the manganese-stabilizing protein, cytochrome c(550), and PsbU. To elucidate the effect of the presence of these extrinsic proteins on the stabilization of the oxygen-evolving machinery against high-temperature stress, we inactivated the genes for these proteins individually in Synechocystis sp. PCC 6803 by targeted mutagenesis. The thermal stability of the oxygen-evolving machinery decreased in all mutated cells but the extent of the susceptibility to heat inactivation varied between the photosystems lacking the different extrinsic proteins. Cells that lacked either the manganese-stabilizing protein or cytochrome c(550) were unable to enhance the thermal stability of the oxygen-evolving machinery and, moreover, failed to increase cellular thermotolerance when grown at moderately high temperatures. Our findings indicate that the three extrinsic proteins stabilize the oxygen-evolving machinery independently against high-temperature stress and that the thermal stability of the machinery influences cellular thermotolerance.
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PMID:Protection of the oxygen-evolving machinery by the extrinsic proteins of photosystem II is essential for development of cellular thermotolerance in Synechocystis sp. PCC 6803. 1219 96

During oxygenic photosynthesis, cytochrome c(6) shuttles electrons between the membrane-bound complexes cytochrome bf and photosystem I. Complex formation between Phormidium laminosum cytochrome f and cytochrome c(6) from both Anabaena sp. PCC 7119 and Synechococcus elongatus has been investigated by nuclear magnetic resonance spectroscopy. Chemical-shift perturbation analysis reveals a binding site on Anabaena cytochrome c(6), which consists of a predominantly hydrophobic patch surrounding the heme substituent, methyl 5. This region of the protein was implicated previously in the formation of the reactive complex with photosytem I. In contrast to the results obtained for Anabaena cytochrome c(6), there is no evidence for specific complex formation with the acidic cytochrome c(6) from Synechococcus. This remarkable variability between analogous cytochromes c(6) supports the idea that different organisms utilize distinct mechanisms of photosynthetic intermolecular electron transfer.
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PMID:The interactions of cyanobacterial cytochrome c6 and cytochrome f, characterized by NMR. 1235 67

In the absence of exogenous donors, turnover of 10 molar equivalents of H(2)O(2) by wild-type recombinant cytochrome c peroxidase [CCP(MI)] and its W191F mutant at pH 7.0 occurs by oxidation of endogenous donors on the polypeptide. No O(2) evolution was observed with either enzyme on reaction with 10 molar equivalents of H(2)O(2), eliminating catalase-like activity, but O(2) evolution was observed when 100 molar equivalents of H(2)O(2) were added to the enzymes. Protein dimers were observed by SDS-PAGE following H(2)O(2) turnover by the peroxidases, and dimeric forms of CCP(MI) and CCP(W191) were isolated by gel-permeation chromatography. LC-ESI-MS analysis of the tryptic digests of the dimers revealed the previously reported T(6)-T(6) crosslink and a new crosslink between T(6)-T(26), but no T(26)-T(26) crosslink. The crosslinked tryptic peptides contain the exposed tyrosine residues Tyr36, Tyr39 and Tyr42 (T(6)), and Tyr229 and Tyr236 (T(26)). Addition of a spin trap, 2-methyl-2-nitrosopropane (MNP), to the CCP(MI)/H(2)O(2) reaction resulted in MNP labeling of peptides T(6), T(21) (which contains Tyr153) and T(26). MNP labeling of Tyr236 was found by sequencing peptide T(26). MNP labeling did not compete with dimerization of H(2)O(2)-oxidized CCP(W191F), suggesting that dityrosine formation in this mutant is very rapid owing to the high reactivity of radicals formed on T(6). H(2)O(2)-dependent formation of CCP-cytochrome c heterodimers was observed for both CCP(MI) and W191F in the presence of ferricytochrome c, the oxidized form of CCP's donor substrate. Interestingly, no H(2)O(2)-dependent cytochrome crosslinking to the W51F mutant was observed, even though this mutant underwent extensive homocrosslinking. The translocation of oxidizing equivalents from the heme to the surface residues of CCP is discussed in terms of an antioxidant role for CCP.
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PMID:Different pathways of radical translocation in yeast cytochrome c peroxidase and its W191F mutant on reaction with H(2)O(2) suggest an antioxidant role. 1258 60

N2 fixation is an O2-sensitive process and some filamentous diazotrophic cyanobacteria that grow performing oxygenic photosynthesis confine their N2 fixation machinery to heterocysts, specialized cells that maintain a reducing environment adequate for N2 fixation. Respiration is thought to contribute to the diazotrophic metabolism of heterocysts and the genome of the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 bears three gene clusters putatively encoding cytochrome c oxidases. Transcript analysis of these cox gene clusters through RNA/DNA hybridization identified two cox operons, cox2 and cox3, that are induced after nitrogen step-down in an NtcA- and HetR-dependent manner and appear to be expressed specifically in heterocysts. In contrast, cox1 was expressed only in vegetative cells. Expression of cox2 and cox3 occurred at an intermediate stage (about 9 h) during the process of heterocyst development following nitrogen step-down. Inactivation of genes in the two inducible cox operons, but not separately in either of them, strongly reduced nitrogenase activity and prevented diazotrophic growth in aerobic conditions. These results show that the nitrogen-regulated cytochrome c oxidase-type respiratory terminal oxidases Cox2 and Cox3 are essential for heterocyst function in Anabaena sp. PCC 7120.
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PMID:Cytochrome c oxidase genes required for nitrogenase activity and diazotrophic growth in Anabaena sp. PCC 7120. 1260 31

Nitrotyrosine is widely recognized as a surrogate marker of up-regulated inducible NO synthase expression at sites of inflammation. However, the potential immunogenicity of autologous proteins containing nitrotyrosine has not previously been investigated. Herein, we used the I-E(K)-restricted T cell epitope of pigeon/moth cytochrome c (PCC/MCC(88-103)) to assess the ability of T cells to recognize ligands containing nitrotyrosine. Substitution of the single tyrosine (Y97) in PCC/MCC(88-103) with nitrotyrosine abrogates recognition by the MCC(88-103)-specific T cell hybridoma 2B4. CBA (H2(K)) mice immunized with MCC(88-103) or nitrated MCC(88-103) peptides produce T cell responses that are mutually exclusive. Transgenic mice that constitutively express PCC under the control of an MHC class I promoter are tolerant toward immunization with MCC(88-103), but exhibited a robust immune response against nitrated MCC(88-103). Analysis of T cell hybridomas specific for nitrated-MCC(88-103) indicated that subtle differences in TCR VDJ gene usage are sufficient to allow nitrotyrosine-specific T cells to escape the processes of central tolerance.
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PMID:Cutting edge: MHC class II-restricted peptides containing the inflammation-associated marker 3-nitrotyrosine evade central tolerance and elicit a robust cell-mediated immune response. 1284 13

This work presents an improved stopped-flow protocol for the simultaneous measurement of thermodynamic and kinetic protein stability data from a single experiment, along with a formalism for the global analysis of the data. The method was applied to the comparison of the stabilities of cytochrome c(6) from Anabaena sp. PCC 7119 and one of its mutants (D72K). Compared to the wild type the mutant was found to have a significantly reduced thermodynamic (deltadeltaG(U0)=2.7 kJ mol(-1)) and kinetic stability, as well as a more pronounced shift in transition state structure upon destabilization.
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PMID:Analysis of the stability of cytochrome c(6) with an improved stopped-flow protocol. 1451 73


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