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

Cyanobacterial thylakoids catalyze both photosynthetic and respiratory activities. In a photosystem I-less Synechocystis sp. PCC 6803 strain, electrons generated by photosystem II appear to be utilized by cytochrome oxidase. To identify the lumenal electron carriers (plastocyanin and/or cytochromes c553, c550, and possibly cM) that are involved in transfer of photosystem II-generated electrons to the terminal oxidase, deletion constructs for genes coding for these components were introduced into a photosystem I-less Synechocystis sp. PCC 6803 strain, and electron flow out of photosystem II was monitored in resulting strains through chlorophyll fluorescence yields. Loss of cytochrome c553 or plastocyanin, but not of cytochrome c550, decreased the rate of electron flow out of photosystem II. Surprisingly, cytochrome cM could not be deleted in a photosystem I-less background strain, and also a double-deletion mutant lacking both plastocyanin and cytochrome c553 could not be obtained. Cytochrome cM has some homology with the cytochrome c-binding regions of the cytochrome Caa3-type cytochrome oxidase from Bacillus spp. and Thermus thermophilus. We suggest that cytochrome cM is a component of cytochrome oxidase in cyanobacteria that serves as redox intermediate between soluble electron carriers and the cytochrome aa3 complex, and that either plastocyanin or cytochrome c553 can shuttle electrons from the cytochrome b6f complex to cytochrome cM.
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PMID:Lumenal proteins involved in respiratory electron transport in the cyanobacterium Synechocystis sp. PCC6803. 934 64

The genome of Synechocystis sp. PCC 6803 contains three sets of genes for terminal respiratory oxidases: the previously identified cytochrome aa3-type cytochrome c oxidase (CtaI), a second putative oxidase (CtaII) that we interpret to be a cytochrome bo-type quinol oxidase, and a putative cytochrome bd quinol oxidase (Cyd). Genes for the two putative oxidases were cloned, and deletion constructs were made. Strains that lack one, two, or all three of the oxidases were generated. Deletion of the respiratory oxidases had no effect on photoautotrophic or photomixotrophic growth. Strains that lack one oxidase respire at near-wild-type rates, whereas those that lack both CtaI and Cyd do not respire. Thus, CtaII does not play a significant role in cellular metabolism under the conditions tested. An expression construct containing cydAB from Synechocystis sp. PCC 6803 was able to restore aerobic growth in a strain of Escherichia coli that lacks the cytochrome bo oxidase and the cytochrome bd oxidase encoded by cydAB. These results show that the cydAB operon from Synechocystis sp. PCC 6803 encodes a functional quinol oxidase. Deletion of Cyd and/or CtaII in strains lacking photosystem I did not change the fluorescence decay kinetics after illumination, and therefore, these oxidases do not significantly utilize reducing equivalents in the thylakoid membrane. This, combined with our inability to delete CtaI from strains lacking photosystem I, suggests that CtaI is the major oxidase on the thylakoid membrane and that Cyd is localized mostly on the cytoplasmic membrane. Transcripts for ctaDI were detected under all growth conditions tested, while transcripts for cydA and ctaEII could only be detected in cells grown at low light intensity (5 microE m(-2) s(-1)).
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PMID:Quinol and cytochrome oxidases in the cyanobacterium Synechocystis sp. PCC 6803. 992 62

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

Non-photochemical redox changes of the plastoquinone pools in darkness were investigated in the cyanobacterium Synechocystis sp. PCC 6803 by monitoring changes in Chl fluorescence yield during light-to-dark transitions. The inhibitors rotenone and mercury with or without 1 mM succinate fully suppressed the post-illumination increase in Chl fluorescence in both NADPH dehydrogenase-defective (M55) and deltaCtaI cells. The latter cells lack subunit I of cytochrome aa3-type cytochrome c oxidase. These results strongly suggest that NADPH dehydrogenase plays the major role in electron donation in the non-photo-chemical reduction of plastoquinone. The rising phase of post-illumination Chl fluorescence in both wild type pretreated with KCN, and deltaCtaI cells, was significantly slowed by low light illumination. We detected comparable photochemical levels of both photosystem (PS) II and PSI during steady state illumination in wild type and deltaCtaI cells. From these results, we suggest that respiratory electron flow involved in the non-photochemical redox change of plastoquinone is not likely to occur in the light.
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PMID:NADPH dehydrogenase-mediated respiratory electron transport in thylakoid membranes of the cyanobacterium Synechocystis sp. PCC 6803 is inactive in the light. 1280 88