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The high potential cytochrome b-559 of intact spinach chloroplasts was photooxidized by red light with a high quantum efficiency and by far-red light with a very low quantum efficiency, when electron flow from water to Photosystem II was inhibited by a carbonyl cyanide phenylhydrazone (FCCP or CCP). Dithiothreitol, which reacts with FCCP or CCCP, reversed the photooxidation of cytochrome b-559 and restored the capability of the chloroplasts to photoreduce CO2 showing that the FCCP/CCCP effects were reversible. The quantum efficiency of cytochrome b-559 photooxidation by red or far-red light in the presence of FCCP was increased by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone which blocks oxidation of reduced plastoquinone by Photosystem I. When the inhibition of water oxidation by FCCP or CCP was decreased by increased light intensities, previously photooxidized cytochrome b-559 was reduced. Red light was much more effective in photoreducing oxidized high potential cytochrome b-559 than far-red light. The red/far-red antagonism in the redox state of cytochrome b-559 is a consequence of the different sensitivity of the cytochrome to red and far-red light and does not indicate that the cytochrome is in the main path of electrons from water to NADP. Rather, cytochrome b-559 acts as a carrier of electrons in a cyclic path around Photosystem II. The redox state of the cytochrome was shifted to the oxidized side when electron transport from water became rate-limiting, while oxidation of water and reduction of plastoquinone resulted in its shifting to the reduced side.
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PMID:Photoreactions of Cytochrome b-559 and cyclic electron flow in photosystem II of intact chloroplasts. 44 98

The thylakoid membrane cytochrome b6-f complex (plastoquinol:oxidized-plastocyanin oxidoreductase, EC 1.10.99.1) catalyzes electron-transfer and proton-translocation reactions essential for oxygenic photosynthesis. We have isolated and determined the nucleotide sequences of the petC and petA genes encoding the Rieske Fe-S and cytochrome f polypeptides from the filamentous cyanobacterium Nostoc PCC 7906. These genes occur as single genomic copies, are tightly linked, and, as indicated by hybridization of gene-specific probes to Nostoc RNA, are cotranscribed as a 2.0-kilobase message. The Rieske Fe-S/cytochrome f gene pair thus represents an example of clustering and cotranscription in cyanobacteria of functionally related genes that, in photosynthetic eukaryotes, reside on separate nuclear and plastid genomes. These data are consistent with the progressive degeneration of the modern chloroplast genome from the ancestral, cyanobacterial-like genome of an endosymbiont. The Rieske Fe-S and the mature cytochrome f apoproteins are encoded by 537 and 867 nucleotides and have molecular masses of 19.2 and 31.2 kDa, respectively. They show 59% and 60% protein sequence identity, respectively, relative to spinach. Forty-four amino acids (4.7 kDa) resembling a prokaryotic signal sequence precede apocytochrome f. In contrast, the Rieske Fe-S protein appears to be translated without a presequence. The 183 bases separating the Rieske Fe-S and preapocytochrome f genes contain two families of 7- to 9-base tandem repeats, and some part of this sequence is highly reiterated in the genome. The C terminus of the Rieske Fe-S protein contains cysteine and histidine residues (probable ligands for the Fe2S2 center) in two peptides, Cys-Thr-His-Leu-Gly-Cys-Val and Cys-Pro-Cys-His-Gly-Ser, which have been conserved in spinach and in the five available Rieske Fe-S sequences from the mitochondrial-type cytochrome b-c1 complexes. Cytochrome f shows the heme binding residues Cys-Xaa-Xaa-Cys-His near its N terminus. Single, long hydrophobic stretches occur near the N and C termini, respectively, of the Rieske Fe-S and cytochrome f proteins and may form membrane-spanning helices.
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PMID:Primary structure of cotranscribed genes encoding the Rieske Fe-S and cytochrome f proteins of the cyanobacterium Nostoc PCC 7906. 284 48

We have isolated and determined the nucleotide and derived protein sequences for the four genes, petCA and BD, which encode the cytochrome b6-f, electron-transfer complex of the filamentous cyanobacterium, Nostoc PCC 7906. The primary structure and cotranscription of the petCA genes encoding the Rieske-FeS (nuclear encoded in plants) and apocytochrome f proteins has been described previously (Kallas, T., Spiller, S., and Malkin, R. (1988) Proc. Natl. Acad. Sci. U.S.A., in press). The petBD genes (645 and 480 protein-coding nucleotides, respectively) for the apocytochrome b6 (24.3 kDa) and subunit-IV (17.5 kDa) proteins comprise a second operon located at least 12 kilobases (kb) from petCA. The Nostoc petBD genes are not closely linked to the psbB gene (encoding the 51-kDa photosystem II polypeptide) and do not contain introns as do the closely related chloroplast genes. DNA probes specific for each of the Nostoc cytochrome-complex genes hybridized to single bands in genomic DNA blots at intensities expected for single copy genes. These data suggest that a single set of cytochrome b6-f proteins function in the different types of membranes found in Nostoc vegetative and heterocyst cells. RNA blot hybridizations identified an 1.8-kb mRNA common to cytochrome b6 and subunit IV, and an intensely hybridizing 0.8-kb mRNA specific to the subunit IV gene probe. The role of the latter RNA is not clear but it may represent a transcript from the opposite strand. The deduced Rieske, apocytochrome f, apocytochrome b6, and subunit IV proteins exhibit 59, 58-63, 84-85, and 79-83% sequence identity with the proteins from chloroplast cytochrome b6-f complexes. The Nostoc proteins show lower but still significant sequences identity with the corresponding proteins of the mitochondrial-type b-c1 complexes. The four probable heme-liganding His residues, and the approximate spacings between them, have been conserved in all of the available cytochrome b6 and b sequences from divergent sources. The Nostoc apocytochrome b6 and subunit IV proteins, as well as the Rieske, appear to be translated and thus inserted into the membrane as mature forms without cleavable presequences. Hydropathy analyses revealed five potential membrane spans in cytochrome b6 and three in the subunit IV protein, consistent with the profiles observed for the chloroplast proteins and the related cytochrome b proteins of cytochrome b-c1 complexes.
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PMID:Characterization of two operons encoding the cytochrome b6-f complex of the cyanobacterium Nostoc PCC 7906. Highly conserved sequences but different gene organization than in chloroplasts. 284 67

The topography of the heme prosthetic group of cytochrome b-559 of the photosystem II reaction center was determined from measurement of the orientation of its alpha- and beta-polypeptides in thylakoid membranes of spinach chloroplasts and in osmotically disrupted cells of the cyanobacterium Synechocystis sp. PCC 6803. The accessibility to trypsin proteolysis of an epitope located near the solvent-exposed N-terminus of the beta-subunit was compared to that of the alpha-subunit, whose N- and C-termini had previously been localized from the trypsinolysis pattern to the stromal and lumenal sides of spinach thylakoid membranes, respectively [Tae et al. (1988) Biochemistry 27, 9075-9080; Vallon et al. (1989) Biochim. Biophys. Acta 975, 132-141]. The N-terminal epitope of the cyanobacterial beta-subunit was modified by introducing a tridecapeptide epitope, previously found to be immunoreactive, from the C-terminal region of the spinach chloroplast alpha-subunit. This epitope had no homology with the cyanobacterial alpha-subunit. The cells with the hybrid beta-subunit retained full photosynthetic activity. The intactness of membranes from osmotically shocked cyanobacteria was tested by trypsin inaccessibility to (a) the alpha-subunit C-terminus and (b) the manganese-stabilizing protein (MSP) of the oxygen-evolving complex that is on the lumenal side of the membrane. The loss after trypsinolysis of most of the beta-subunit immunoreactivity, under conditions where (i) the alpha-subunit was cleaved near the N-terminus in both spinach thylakoids and osmotically shocked cyanobacterial membranes and (ii) the MSP protein in cyanobacteria was not disrupted, implied that the orientation of the beta-subunit was parallel to that of the alpha-subunit in both kinds of membranes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Topography of the heme prosthetic group of cytochrome b-559 in the photosystem II reaction center. 806 Sep 75

Cytochrome b-559 is an integral component of photosystem II complexes from both plants and cyanobacteria. However, the number of cytochrome b-559 associated with the photosystem II reaction center has been the subject of controversy. Some studies have concluded that there is one heme equivalent of cytochrome b-559 per reaction center, some studies have found two, and some studies have reported intermediate values. Most of the previous experiments have used only one method to quantitate the antenna size of the preparation. In this study, we compare the cytochrome b-559 content in a cyanobacterial and a plant photosystem II preparation. The plant preparation is derived from spinach, and previous work has shown that it has an antenna size of approximately 100 chlorophylls [MacDonald, G. M., & Barry, B. A. (1992) Biochemistry 31, 9848-9856]. The cyanobacterial preparation is from Synechocystis sp. PCC 6803, and previous work has shown that it has an antenna size of approximately 60 chlorophylls [Noren, G. H., Boerner, R. J., & Barry, B. A. (1991) Biochemistry 30, 3943-3950]. Both preparations are isolated through the use of ion-exchange chromatography, and both preparations are monodisperse in the same nonionic detergent. In our comparative study, we quantitate antenna size by three different methods. Our work shows that, depending on the method used to estimate antenna size, the oxygen-evolving spinach photosystem II preparation contains 0.82-1.0 cytochrome b-559 per reaction center, while the oxygen-evolving cyanobacterial preparation contains 1.5-2.1 cytochrome b-559 per reaction center.
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PMID:Comparison of cytochrome b-559 content in photosystem II complexes from spinach and Synechocystis species PCC 6803. 815 57

Photosystem I and II core complexes were resolved in a single step from the thylakoid membrane of Synechocystis sp. PCC 6803 by using a mild solubilization procedure in dodecyl beta-D-maltoside and Deriphat/PAGE. For each photosystem, two green bands were obtained containing oligomeric and monomeric forms of the core complexes of either photosystem. The oligomers are likely to be trimers in the case of photosystem I and dimers for photosystem II. The absorption spectra, polypeptide and pigment composition of green bands corresponding to either photosystem I or photosystem II were identical for monomeric and oligomeric forms. The cytochrome b-559 content of photosystem II was evaluated to be one cytochrome b-559/reaction centre both in the monomeric and dimeric forms. Two new 15-kDa and 22-kDa carotenoid-binding protein were isolated and their polypeptides purified to homogeneity.
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PMID:Pigment-protein complexes from the photosynthetic membrane of the cyanobacterium Synechocystis sp. PCC 6803. 853 89

Cytochrome c maturation involves heme transport and covalent attachment of heme to the apoprotein. The 5' end of the ccsB gene, which is involved in the maturation process and resembles the ccs1 gene from Chlamydomonas reinhardtii, was replaced by a chloramphenicol resistance cartridge in the cyanobacterium Synechocystis sp. PCC 6803. The resulting Delta(M1-A24) mutant lacking the first 24 ccsB codons grew only under anaerobic conditions. The mutant retained about 20% of the wild-type amount of processed cytochrome f with heme attached, apparently assembled in a functional cytochrome b(6)f complex. Moreover, the mutant accumulated unprocessed apocytochrome f in its membrane fraction. A pseudorevertant was isolated that regained the ability to grow under aerobic conditions. The locus of the second-site mutation was mapped to ccsB, and the mutation resulted in the formation of a new potential start codon in the intergenic region, between the chloramphenicol resistance marker and ccsB, in frame with the remaining part of ccsB. In this pseudorevertant the amount of holocyt f increased, whereas that of unprocessed apocytochrome f decreased. We suggest that the original deletion mutant Delta(M1-A24) expresses an N-terminally truncated version of the protein. The stable accumulation of unprocessed apocytochrome f in membranes of the Delta(M1-A24) mutant may be explained by its association with truncated and only partially functional CcsB protein resulting in protection from degradation. Our attempt to delete the first 244 codons of ccsB in Synechocystis sp. PCC 6803 was not successful, suggesting that this would lead to a lack of functional cytochrome b(6)f complex. The results suggest that the CcsB protein is an apocytochrome chaperone, which together with CcsA may constitute part of cytochrome c lyase.
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PMID:Accumulation of pre-apocytochrome f in a Synechocystis sp. PCC 6803 mutant impaired in cytochrome c maturation. 1054 82

We investigated the role of the redox state of the photosynthetic and respiratory electron transport chains on the regulation of psbA expression in Synechocystis PCC 6803. Different means to modify the redox state of the electron carriers were used: (a) dark to oxidize the whole electron transport chain; (b) a shift from dark to light to induce its reduction; (c) the chemical interruption of the electron flow at different points to change the redox state of specific electron carriers; and (d) the presence of glucose to maintain a high reducing power in darkness. We show that changes in the redox state of the intersystem electron transport chain induce modifications of psbA transcript production and psbA mRNA stability. Reduction of the intersystem electron carriers activates psbA transcription and destabilizes the mRNA, while their oxidation induces a decrease in transcription and a stabilization of the transcript. Furthermore, our data suggest that the redox state of one of the electron carriers between the plastoquinone pool and photosystem I influences not only the expression of the psbA gene, but also that of other two photosynthetic genes, psaE and cpcBA. As a working hypothesis, we propose that the occupancy of the Q(0) site in the cytochrome b(6)/f complex may be involved in this regulation.
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PMID:Redox control of psbA gene expression in the cyanobacterium Synechocystis PCC 6803. Involvement of the cytochrome b(6)/f complex. 1067 43

The genes encoding cytochrome f (petA), cytochrome b(6) (petB), the Rieske FeS-protein (petC), and subunit IV (petD) of the cytochrome b(6)f complex from the thermophilic cyanobacterium Synechococcus elongatus were cloned and sequenced. Similar to other cyanobacteria, the structural genes are arranged in two short, single-copy operons, petC/petA and petB/petD, respectively. In addition, five open reading frames with homology to known orfs from the cyanobacterium Synechocystis PCC 6803 were identified in the immediate vicinity of these two operons.
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PMID:Sequence of the two operons encoding the four core subunits of the cytochrome b(6)f complex from the thermophilic Cyanobacterium synechococcus elongatus. 1076 Jun 4

Relative to ferredoxin:NADP(+) reductase (FNR) from chloroplasts, the comparable enzyme in cyanobacteria contains an additional 9 kDa domain at its amino-terminus. The domain is homologous to the phycocyanin associated linker polypeptide CpcD of the light harvesting phycobilisome antennae. The phenotypic consequences of the genetic removal of this domain from the petH gene, which encodes FNR, have been studied in Synechocystis PCC 6803. The in frame deletion of 75 residues at the amino-terminus, rendered chloroplast length FNR enzyme with normal functionality in linear photosynthetic electron transfer. Salt shock correlated with increased abundance of petH mRNA in the wild-type and mutant alike. The truncation stopped salt stress-inducible increase of Photosystem I-dependent cyclic electron flow. Both photoacoustic determination of the storage of energy from Photosystem I specific far-red light, and the re-reduction kinetics of P700(+), suggest lack of function of the truncated FNR in the plastoquinone-cytochrome b(6)f complex reductase step of the PS I-dependent cyclic electron transfer chain. Independent gold-immunodecoration studies and analysis of FNR distribution through activity staining after native polyacrylamide gelelectrophoresis showed that association of FNR with the thylakoid membranes of Synechocystis PCC 6803 requires the presence of the extended amino-terminal domain of the enzyme. The truncated DeltapetH gene was also transformed into a NAD(P)H dehydrogenase (NDH1) deficient mutant of Synechocystis PCC 6803 (strain M55) (T. Ogawa, Proc. Natl. Acad. Sci. USA 88 (1991) 4275-4279). Phenotypic characterisation of the double mutant supported our conclusion that both the NAD(P)H dehydrogenase complex and FNR contribute independently to the quinone cytochrome b(6)f reductase step in PS I-dependent cyclic electron transfer. The distribution, binding properties and function of FNR in the model cyanobacterium Synechocystis PCC 6803 will be discussed.
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PMID:Salt shock-inducible photosystem I cyclic electron transfer in Synechocystis PCC6803 relies on binding of ferredoxin:NADP(+) reductase to the thylakoid membranes via its CpcD phycobilisome-linker homologous N-terminal domain. 1077 58

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