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

Cytochrome c-552 (soluble 'cytochrome f') from the unicellular cyanobacterium Synechococcus PCC 6312 (ATCC 27167) was purified and the primary structure determined. The proposed sequence consists of one polypeptide chain of 87 residues. The sequence was determined by a combination of chemical and enzymatic cleavage, manual and automatic sequencing and mass spectroscopy. This is the first amino acid sequence of this cytochrome from a unicellular cyanobacterium to be determined in a study of the variation in primary structure between phylogenetically distant cyanobacteria. The sequence is compared to the primary structures of the cytochrome from filamentous cyanobacteria and from eukaryotic algae. The significance of these sequence comparisons to the current hypotheses concerning the origin of eukaryotic cells and their chloroplasts is discussed.
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PMID:Purification and primary structure of cytochrome c-552 from the cyanobacterium, Synechococcus PCC 6312. 22 36

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 effect of copper on the levels of plastocyanin (PC) and cytochrome c553 (cyt-c)-specific transcripts from Anabaena sp. PCC 7937 was investigated. The addition of copper resulted in a marked increase in PC mRNA levels, and a decrease in cyt c mRNA levels. Thus the functional exchange between PC and cyt c seems to be regulated at the mRNA level. The copper-dependent increase in PC and decrease in cyt c mRNA levels was abolished when chloramphenicol was added to the cells. This suggests that de novo synthesis of at least one trans-acting element is required to regulate PC and cyt c mRNA levels. Both PC and cyt c mRNA stability was found to be unaltered under varying Cu2+ regimes. This leads to the conclusion that expression of both genes is regulated at the level of initiation of transcription.
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PMID:Transcriptional regulation of the plastocyanin and cytochrome c553 genes from the cyanobacterium Anabaena species PCC 7937. 132 Jul 27

The genes encoding the photosynthetic cytochrome b6 (petB) and subunit 4 (petD) have been cloned and sequenced from the unicellular, photoheterotrophic, transformable cyanobacterium Synechococcus sp. PCC 7002, formerly designated Agmenellum quadruplicatum. The gene arrangement was found to be similar to that reported in the cyanobacterium Nostoc PCC 7906. The DNA and derived protein sequences were compared to chloroplast and the other cyanobacterial sequences. By pulsed-field electrophoresis, the petBD operon and the petCA operon, encoding the Rieske iron-sulfur protein and cytochrome f, were found to be located on separate, unlinked, Not I-digested DNA fragments. The petBD operon was found on the third largest Not I fragment (NC-325) while the petCA operon was found on the second largest Not I fragment (NB-370). These results suggest the two operons are not in proximity. The 1.35 kb transcript was shown to be light-regulated. Transcripts from cells grown under constant illumination showed a decrease in petB transcript levels to undetectable levels within 2 h after the cells were placed in the dark. Upon reillumination, transcript levels rose to three-fold over that seen initially under constant illumination.
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PMID:Cloning and sequencing of the petBD operon from the cyanobacterium Synechococcus sp. PCC 7002. 142 Nov 51

The enzyme superoxide dismutase is ubiquitous in aerobic organisms where it plays a major role in alleviating oxygen-radical toxicity. An insertion mutation introduced into the iron superoxide dismutase locus (designated sodB) of the cyanobacterium Synechococcus sp. PCC 7942 created a mutant strain devoid of detectable iron superoxide dismutase activity. Both wild-type and mutant strains exhibited similar photosynthetic activity and viability when grown with 17 mumol.m-2.s-1 illumination in liquid culture supplemented with 3% carbon dioxide. In contrast, the sodB mutant exhibited significantly greater damage to its photosynthetic system than the wild-type strain when grown under increased oxygen tension or with methyl viologen. Although damage occurs at both photosystems I and II, it is primarily localized at photosystem I in the sodB mutant. Growth in 100% molecular oxygen for 24 hr decreased photoacoustically measured energy storage in 3-(3,4-dichlorophenyl)-1,1-dimethylurea and abolished the fluorescence state 2 to state 1 transition in the sodB mutant, indicating interruption of cyclic electron flow around photosystem I. Analysis of the flash-induced absorption transient at 705 nm indicated that the interruption of cyclic electron flow occurred in the return part of the cycle, between the two [4 Fe-4 S] centers of photosystem I, FA and FB, and cytochrome f. Even though the sodB mutant was more sensitive to damage by active oxygen than wild-type cells, both strains were equally sensitive to the photoinhibition of photosystem II caused by exposure to strong light.
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PMID:Characterization of damage to photosystems I and II in a cyanobacterium lacking detectable iron superoxide dismutase activity. 152 84

The COOH-terminal domain of the 80-residue cytochrome b559 alpha-subunit (psbE gene product) in Synechocystis sp. PCC 6803 was sequentially truncated in order to determine the minimum polypeptide length needed for function and assembly. A stop codon was introduced into the Arg-50, Arg-59, or Tyr-69 codons of the psbE gene, generating mutants truncated by 31, 22, and 12 residues, respectively. Removal of 12 residues caused a decrease of 20% in PSII function. Truncation of 22 or 31 residues caused a large decrease (60-85%) in the photoautotrophic growth rate, the rate of O2 evolution, and the amplitude of the 77 K 696-nm fluorescence, and a concomitant increase in the constant yield fraction (F0/Fmax) of the chlorophyll fluorescence. The level of residual activity in the Arg50-stop mutant was 10-20% of the wild type, which was reflected in a similar low level of immunochemically detected D2 polypeptide. Quantitation of the PSII reaction center stoichiometry of the Arg50-stop mutant by analysis of [14C]DCMU binding also showed a 5-fold decrease (1:910 Chl in wild type and 1:5480 Chl in R50) in the PSII reaction center concentration. However, the KD value for DCMU in the residual 15% of the complexes to which it bound was approximately equal to that (25 nM) of the wild type. Northern blot analysis showed no decrease in the b559 psbE mRNA level. Chemical difference spectral analysis of heme content indicated that the level of native cytochrome b559 heme in the Arg50-stop mutant (1:640 Chl) was 80% that of wild type (1:510 Chl).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Truncation of the COOH-terminal domain of the psbE gene product in Synechocystis sp. PCC 6803: requirements for photosystem II assembly and function. 156 53

The reaction center core of photosystem II, a multiprotein membrane bound complex, is composed of a heterodimer of two proteins, D1 and D2. A random mutagenesis technique was used to isolate a photosystem II deficient mutant, CP6t16, of the unicellular cyanobacterium, Synechocystis sp. PCC 6803. Nucleotide sequence analysis showed that the primary lesion in CP6t16 is an ochre mutation introducing a translational stop codon in the psbE gene, encoding the alpha-subunit of cytochrome b559, an integral component of the PSII complex. Analysis of the protein composition of CP6t16 thylakoid membranes isolated in the presence of serine protease inhibitors revealed that, in the absence of cytochrome b559, the D2 protein is also absent. However, the D1 protein is stably incorporated in these membranes, suggesting that the synthesis and integration of D1 are independent of those of D2 and cytochrome b559.
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PMID:The D1 protein of the photosystem II reaction-centre complex accumulates in the absence of D2: analysis of a mutant of the cyanobacterium Synechocystis sp. PCC 6803 lacking cytochrome b559. 160 69

Methods are described for the simultaneous isolation of ferredoxin-NADP+ reductase, ferredoxin and flavodoxin from large quantities of the cyanobacterium Anabaena PCC 7119 allowing the use of a single batch of cells. The ultraviolet-visible spectra and the extinction coefficients of ferredoxin-NADP+ reductase and ferredoxin were determined. The purification procedure also yields enriched fractions of phycobiliproteins and cytochrome c553.
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PMID:Purification of ferredoxin-NADP+ reductase, flavodoxin and ferredoxin from a single batch of the cyanobacterium Anabaena PCC 7119. 166 99

Flavodoxin from the nitrogen-fixing cyanobacteria Anabaena PCC 7119 forms an electron-transfer complex with ferredoxin--NADP+ reductase (FNR) from the same organism. The complex is mainly governed by electrostatic interactions between side-chain amino groups of the reductase and carboxyl residues of flavodoxin. In order to localize the binding site on flavodoxin, chemical modification of its carboxyl groups has been carried out. Treatment of flavodoxin with a water-soluble carbodiimide, N-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), in the presence of a nucleophile, glycine ethyl ester, caused a time-dependent modification of the protein that is responsible for the loss of its ability to participate as electron carrier in the photoreduction of NADP+ by chloroplast membranes, and also in NADPH--cytochrome-c reductase activity, by about 85%. Nevertheless, the ability of flavodoxin to receive electrons from the reducing side of photosystem I was much less affected. The inhibition was enhanced at low pH, suggesting that carboxylic acid groups were the target of chemical modification. Treated flavodoxin failed to form covalent complexes with FNR and the dissociation constant for the non-covalent complex with FNR was fourfold higher. After tryptic digestion of a sample of flavodoxin modified by EDC in the presence of [1-14C]glycine ethyl ester, two major radioactive peptides were isolated. The first protein fragment contained three carboxylic residues (Asp123, Asp126 and Asp129), corresponding to the region where long-chain flavodoxins show an insert compared to short-chain flavodoxins. The second peptide corresponded to a similar region, either in the amino acid sequence or in the three-dimensional structure of the protein and also containing three carboxyl groups (Asp144, Glu145 and Asp146). Four of these carboxyl groups (Asp123, Asp126, Asp144 and Asp146) are highly conserved in all long-chain flavodoxins, suggesting that they could play an essential role in substrate recognition.
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PMID:Identification of specific carboxyl groups on Anabaena PCC 7119 flavodoxin which are involved in the interaction with ferredoxin-NADP+ reductase. 173 24

In cyanobacteria, the water-soluble cytochrome c-553 functions as a mobile carrier of electrons between the membrane-bound cytochrome b6-f complex and P-700 reaction centers of Photosystem I. The structural gene for cytochrome c-553 (designated cytA) of the cyanobacterium Synechococcus sp. PCC 7942 was cloned, and the deduced amino acid sequence was shown to be similar to known cyanobacterial cytochrome c-553 proteins. A deletion mutant was constructed that had no detectable cytochrome c-553 based on spectral analyses and tetramethylbenzidine-hydrogen peroxide staining of proteins resolved by polyacrylamide gel electrophoresis. The mutant strain was not impaired in overall photosynthetic activity. However, this mutant exhibited a decreased efficiency of cytochrome f oxidation. These results indicate that cytochrome c-553 is not an absolute requirement for reducing Photosystem I reaction centers in Synechococcus sp. PCC 7942.
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PMID:Cytochrome c-553 is not required for photosynthetic activity in the cyanobacterium Synechococcus. 196 57


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