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Query: UMLS:C1832526 (PCC)
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Isopentenyl diphosphate, the universal isoprenoid precursor, can be produced by two different biosynthetic routes: either via the acetate/mevalonate (MVA) pathway, or via the more recently identified MVA-independent glyceraldehyde phosphate/pyruvate pathway. These two pathways are easily differentiated by incorporation of [1-13C]glucose and analysis of the resulting labelling patterns found in the isoprenoids. This method was successfully applied to several unicellular algae raised under heterotrophic growth conditions and allowed for the identification of the pathways that were utilized for isoprenoid biosynthesis. All isoprenoids examined (sterols, phytol, carotenoids) of the green algae Chlorella fusca and Chlamydomonas reinhardtii were synthesized via the GAP/pyruvate pathway, as in another previously investigated green alga, Scenedesmus obliquus, which was also shown in this study to synthesize ubiquinone by the same MVA-independent route. In the red alga Cyanidium caldarium and in the Chrysophyte Ochromonas danica a clear dichotomy was observed: as in higher plants, sterols were formed via the MVA route, whereas chloroplast isoprenoids (phytol in Cy. caldarium and O. danica and beta-carotene in O. danica) were synthesized via the GAP/pyruvate route. In contrast, the Euglenophyte Euglena gracilis synthesized ergosterol, as well as phytol, via the acetate/MVA route. Similar feeding experiments were performed with the cyanobacterium Synechocystis PCC 6714 using [1-13C]- and [6-13C]-glucose. The two isoprenoids examined, phytol and beta-carotene, were shown to have the typical labelling pattern derived from the GAP/pyruvate route.
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PMID:Distribution of the mevalonate and glyceraldehyde phosphate/pyruvate pathways for isoprenoid biosynthesis in unicellular algae and the cyanobacterium Synechocystis PCC 6714. 965 79

The photoreduction of the oxidized and the semiquinone form of flavodoxin from Synechocystis sp. PCC 6803 by the photosystem I (PSI) of wild-type Chlamydomonas reinhardtii and the mutant strains Lys35Asp, Lys35Glu and Lys35Arg was analysed by flash-absorption spectroscopy to investigate the role of residue Lys35 of the PSI subunit PsaC in flavodoxin reduction. For PSI preparations from C. reinhardtii the reduction of oxidized flavodoxin was monoexponential and approached limiting electron transfer rates similar to those of cyanobacterial PSI from the wild-type and the Lys35Arg mutant. For PSI from the Lys35Glu mutant, however, a approximately 2.5-fold smaller value was determined. The photoreduction of flavodoxin semiquinone by PSI from C. reinhardtii lacked fast first-order kinetic components and, in contrast with PSI from cyanobacteria, displayed only a single concentration-dependent phase. From this phase, second-order rate constants were calculated for wild-type PSI and PSI from the Lys35Arg mutant which were comparable to those of PSI from cyanobacteria. For PSI from the Lys35Glu and the Lys35Asp mutants the derived second-order rate constants were 19 and 10 times smaller. Thus, the inversion of charge at position 35 of PsaC negatively affects the rate of electron transfer to both forms of flavodoxin, whereas PSI complexes that retain a positive charge at this position show wild-type kinetics. However, the positive charge at this position of PsaC is not essential for flavodoxin photoreduction as the number of flavodoxin molecules reduced per PSI was similar for all of the PSI complexes investigated. In addition, chemical cross-linking assays showed that the binary cross-linking product between flavodoxin and PsaC of PSI from wild-type C. reinhardtii was not formed with PSI complexes from the Lys13Asp and Lys35Glu mutants. This indicates that Lys35 of PsaC is probably essential for the chemical cross-link between PsaC and flavodoxin. Taken together, these experiments show that Lys35 of PsaC plays a strikingly similar role in the electron transfer from PSI to both ferredoxin and flavodoxin.
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PMID:Lys35 of PsaC is required for the efficient photoreduction of flavodoxin by photosystem I from Chlamydomonas reinhardtii. 1042 97

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

A putative hemoglobin (Hb) gene, related to those previously characterized in the green alga Chlamydomonas eugametos, the ciliated protozoan Paramecium caudatum, the cyanobacterium Nostoc commune and the bacterium Mycobacterium tuberculosis, was recently discovered in the complete genome sequence of the cyanobacterium Synechocystis PCC 6803. In this paper, we report the purification of Synechocystis Hb and describe some of its salient biochemical and spectroscopic properties. We show that the recombinant protein contains Fe-protoporphyrin IX and forms a very stable complex with oxygen. The oxygen dissociation rate measured, 0.011 s(-1), is among the smallest known and is four orders of magnitude smaller than the rate measured for N. commune Hb, which suggests functional differences between these Hbs. Optical and resonance Raman spectroscopic study of the structure of the heme pocket of Synechocystis Hb reveals that the heme is 6-coordinate and low-spin in both ferric and ferrous forms in the pH range 5.5-10.5. We present evidence that His46, predicted to occupy the helical position E10 based on amino-acid sequence comparison, is involved in the formation of the ferric and ferrous 6-coordinate low-spin structures. The analysis of the His46Ala mutant shows that the ferrous form is 5-coordinate and high-spin and the ferric form contains a 6-coordinate high-spin component in which the sixth ligand is most probably a water molecule. We conclude that the heme pocket of the wild type Synechocystis Hb has a unique structure that requires a histidine residue at the E10 position for the formation of its native structure.
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PMID:Structural investigations of the hemoglobin of the cyanobacterium Synechocystis PCC6803 reveal a unique distal heme pocket. 1090 11

The catalytic site for photosynthetic water oxidation is embedded in a protein matrix consisting of nearly 30 different polypeptides. Residues from several of these polypeptides modulate the properties of the tetrameric Mn cluster and the redox-active tyrosine residue, Y(Z), that are located at the catalytic site. However, most or all of the residues that interact directly with Y(Z) and the Mn cluster appear to be contributed by the D1 polypeptide. This review summarizes our knowledge of the environments of Y(Z) and the Mn cluster as obtained from the introduction of site-directed, deletion, and other mutations into the photosystem II polypeptides of the cyanobacterium Synechocystis sp. PCC 6803 and the green alga Chlamydomonas reinhardtii.
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PMID:Amino acid residues that modulate the properties of tyrosine Y(Z) and the manganese cluster in the water oxidizing complex of photosystem II. 1111 32

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

Light-induced Fourier transform infrared (FTIR) difference spectroscopy has been used to study the photo-oxidation of the primary electron donor (P700) in PS I particles from Chlamydomonas reinhardtii and Synechocystis sp. PCC 6803. To aid in the interpretation of the spectra, PS I particles from a site-directed mutant of C. reinhardtii, in which the axial histidine ligand (HisA676) was changed to serine, were also studied. A high-frequency (3300-2600 cm(-1)) electronic transition is observed for all PS I particles, demonstrating that P700 is dimeric. The electronic band is, however, species-dependent, indicating some differences in the electronic structure of P700 and/or P700(+) in C. reinhardtii and Synechocystis sp. 6803. For PS I particles from C. reinhardtii, substitution of HisA676 with serine has little effect on the ester carbonyl modes of the chlorophylls of P700. However, the keto carbonyl modes are considerably altered. Comparison of (P700(+) - P700) FTIR difference spectra obtained using PS I particles from the wild type (WT) and the HS(A676) mutant of C. reinhardtii indicates that the mutation primarily exerts its influence on the P700 ground state. The 13(1) keto carbonyls of the chlorophylls of P700 of the wild type absorb at similar frequencies, which has previously made these transitions difficult to resolve. However, for the HS(A676) mutant, the 13(1) keto carbonyl of chlorophyll a or chlorophyll a' of P700 on PsaB or PsaA absorbs at 1703.4 or 1694.2 cm(-1), respectively, allowing their unambiguous resolution. Upon P700(+) formation, in both PS I particles from C. reinhardtii, the higher-frequency carbonyl band upshifts by approximately 14 cm(-1) while the lower frequency carbonyl downshifts by approximately 10 cm(-1). The similarity in the spectra for WT PS I particles from C. reinhardtii and Synechocystis sp. 6803 indicates that a similar interpretation is probably valid for PS I particles from both species. The mutant results allow for an interpretation of the behavior of the 13(1) keto carbonyls of P700 that is different from previous work [Breton, J., Nabedryk, E., and Leibl, W. (1999) Biochemistry 38, 11585-11592], in which it was suggested that 13(1) keto carbonyls of P700 absorb at 1697 and 1639 cm(-1), and upshift by 21 cm(-1) upon cation formation. The interpretation of the spectra reported here is more in line with recent results from ENDOR spectroscopy and high-resolution crystallography.
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PMID:Primary donor photo-oxidation in photosystem I: a re-evaluation of (P700(+) - P700) Fourier transform infrared difference spectra. 1166 31

A 4.4-kb HindIII fragment, encoding an unusual rubredoxin (denoted RubA), a homolog of the Synechocystis sp. PCC 6803 gene slr2034 and Arabidopsis thaliana HCF136, and the psbEFLJ operon, was cloned from the cyanobacterium Synechococcus sp. PCC 7002. Inactivation of the slr2034 homolog produced a mutant with no detectable phenotype and wild-type photosystem (PS) II levels. Inactivation of the rubA gene of Synechococcus sp. PCC 7002 produced a mutant unable to grow photoautotrophically. RubA and PS I electron transport activity were completely absent in the mutant, although PS II activity was approximately 80% of the wild-type level. RubA contains a domain of approximately 50 amino acids with very high similarity to the rubredoxins of anaerobic bacteria and archaea, but it also contains a region of about 50 amino acids that is predicted to form a flexible hinge and a transmembrane alpha-helix at its C terminus. Overproduction of the water-soluble rubredoxin domain in Escherichia coli led to a product with the absorption and EPR spectra of typical rubredoxins. RubA was present in thylakoid but not plasma membranes of cyanobacteria and in chloroplast thylakoids isolated from spinach and Chlamydomonas reinhardtii. Fractionation studies suggest that RubA might transiently associate with PS I monomers, but no evidence for an association with PS I trimers or PS II was observed. PS I levels were significantly lower than in the wild type ( approximately 40%), but trimeric PS I complexes could be isolated from the rubA mutant. These PS I complexes completely lacked the stromal subunits PsaC, PsaD, and PsaE but contained all membrane-intrinsic subunits. The three missing proteins could be detected immunologically in whole cells, but their levels were greatly reduced, and degradation products were also detected. Our results indicate that RubA plays a specific role in the biogenesis of PS I.
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PMID:Assembly of photosystem I. I. Inactivation of the rubA gene encoding a membrane-associated rubredoxin in the cyanobacterium Synechococcus sp. PCC 7002 causes a loss of photosystem I activity. 1191 73

The extent of delocalization of the positive charge in the oxidized dimer of chlorophyll (Chl) constituting P700, the primary electron donor of photosystem I (PSI), has been investigated by analyzing the perturbation upon P700(+) formation of infrared (IR) vibrational modes of the two His axial ligands of the two P700 Chl molecules. Fourier transform IR (FTIR) difference spectra of the photooxidation of P700 in PSI core complexes isolated from Synechocystis sp. PCC 6803 isotopically labeled either globally with (15)N or more specifically with (13)C on all the His residues reveal isotopic shifts of a differential signal at 1102/1108 cm(-)(1). This signal is assigned to a downshift upon P700(+) formation of the predominantly C(5)-Ntau imidazole stretching mode of His residue(s). The amplitude of this signal is reduced by approximately half in FTIR spectra of Synechocystis mutants in which His PsaB 651, the axial ligand to one of the two Chl molecules in P700, is replaced by Cys, Gln, or Leu. These observations provide further evidence that the positive charge in P700(+) is essentially delocalized over the two Chl molecules, in agreement with a previous FTIR study in which the frequency of the vibrational modes of the 9-keto and 10a-ester C=O groups of the two Chl's in P700, P700(+), and (3)P700 were firmly established for the first time [Breton, J., et al. (1999) Biochemistry 38, 11585-11592]. Only limited perturbations of the amplitude and frequency of the 9-keto and 10a-ester C=O bands of the P700 Chl are elicited by the mutations. On the basis of comparable mutational studies of the primary electron donor in purple bacteria, these perturbations are attributed to small molecular rearrangements of the Chl macrocycle and substituents caused by the repositioning of the P700 dimer in the new protein cavity generated by the mutations. It is proposed that the perturbation of the FTIR spectra upon mutation of a His axial ligand of the P700 Chl recently reported in Chlamydomonas reinhardtii [Hastings, G., et al. (2001) Biochemistry 40, 12943-12949] can be explained by the same effect without the need for a new assignment of the C=O bands of P700. The distribution of charge/spin in P700(+) and (3)P700 determined by FTIR spectroscopy is discussed in relation with the contrasting interpretations derived from recent magnetic resonance experiments.
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PMID:The two histidine axial ligands of the primary electron donor chlorophylls (P700) in photosystem I are similarly perturbed upon P700+ formation. 1222 Jan 85

A universal structural feature of chlorophyll molecules is the isocyclic ring. This ring is formed by the action of the enzyme Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase, which catalyzes a complex reaction in which Mg-protoporphyrin IX monomethyl ester is converted to divinyl protochlorophyllide (also called Mg-2,4-divinylpheoporphyrin a5), with the participation of NADPH and O2. Cyclase activity was demonstrated in lysed Chlamydomonas reinhardtii chloroplasts and extracts of Synechocystis sp. PCC 6803. The yield of the reaction product was increased by the addition of catalase and ascorbate or isoascorbate to the incubation mixture. These compounds may act by preventing degradation of the tetrapyrroles by reactive oxygen species. Cyclase activity from C. reinhardtii was not inhibited by the flavoprotein inhibitor quinacrine or by the hemoprotein inhibitors CO, KCN, or NaN3. In contrast, cyclase activity in extracts of C. reinhardtii and Synechocystis sp. PCC 6803 was inhibited by chelators of Fe, suggesting that nonheme Fe is involved in the reaction. Cyclase in lysed C. reinhardtii chloroplasts was associated with the membranes, and attempts to further fractionate or solubilize the activity were unsuccessful. In contrast, cyclase in Synechocystis sp. PCC 6803 extracts could be separated into soluble and membrane components, both of which were required for reconstitution of activity. The membrane component retained activity after it was solubilized by the detergent n-octyl-[beta]-D-glucopyranoside in the presence of glycerol and Mg2+. The solubilized membrane component was purified further by dye-affinity and ion-exchange chromatography.
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PMID:The Chlorophyll Biosynthetic Enzyme Mg-Protoporphyrin IX Monomethyl Ester (Oxidative) Cyclase (Characterization and Partial Purification from Chlamydomonas reinhardtii and Synechocystis sp. PCC 6803). 1222 78

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