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

The cyanobacterium Chlorogloeopsis PCC 6912 was found to synthesize and accumulate two putative UV sunscreen compounds of the mycosporine (mycosporine-like amino acid; MAA) type: mycosporine-glycine and shinorine. These MAAs were not constitutively present in the cells; their synthesis could be induced specifically either by exposure to UVB radiation (280-320 nm) or by osmotic stress, but not by other stress factors such as heat or cold shock, nutrient limitation, or photooxidative stress. A significant synergistic enhancement of MAA synthesis was observed when both stress factors were applied in combination. Although osmotic stress could induce MAA synthesis, comparison of the intracellular contents of MAAs with those of sugar osmolytes (glucose and trehalose) indicated that MAAs play no significant role in attaining osmotic homeostasis. UVB strongly enhanced the accumulation of shinorine, whereas osmotic stress had a more pronounced effect on mycosporine-glycine. This differential effect on the steady-state contents of each MAA could be explained either by differential regulation of biosynthesis or by differential loss rates of MAAs (leakage) under each condition. A preferential leakage of mycosporine-glycine from the cells after a hypoosmotic shock was detected. The results are interpreted in terms of an adaptive necessity for a combined regulatory control responding to both UV and external osmotic conditions in organisms that accumulate water-soluble sunscreens intracellularly.
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PMID:Ultraviolet and osmotic stresses induce and regulate the synthesis of mycosporines in the cyanobacterium chlorogloeopsis PCC 6912 1052 34

The feasibility of biologically removing nitrate from groundwater was tested by using cyanobacterial cultures in batch mode under laboratory conditions. Results demonstrated that nitrate-contaminated groundwater, when supplemented with phosphate and some trace elements, can be used as growth medium supporting vigorous growth of several strains of cyanobacteria. As cyanobacteria grew, nitrate was removed from the water. Of three species tested, Synechococcus sp. strain PCC 7942 displayed the highest nitrate uptake rate, but all species showed rapid removal of nitrate from groundwater. The nitrate uptake rate increased proportionally with increasing light intensity up to 100 micromol of photons m(-2) s(-1), which parallels photosynthetic activity. The nitrate uptake rate was affected by inoculum size (i.e., cell density), fixed-nitrogen level in the cells in the inoculum, and aeration rate, with vigorously aerated, nitrate-sufficient cells in mid-logarithmic phase having the highest long-term nitrate uptake rate. Average nitrate uptake rates up to 0.05 mM NO(3-) h(-1) could be achieved at a culture optical density at 730 nm of 0.5 to 1. 0 over a 2-day culture period. This result compares favorably with those reported for nitrate removal by other cyanobacteria and algae, and therefore effective nitrate removal from groundwater using this organism could be anticipated on large-scale operations.
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PMID:Removal of nitrate from groundwater by cyanobacteria: quantitative assessment of factors influencing nitrate uptake. 1061 14

The three-dimensional crystal structure of the Glu301Ala site-directed mutant of ferredoxin-NADP+ reductase from Anabaena PCC 7119 has been determined at 1.8A resolution by x-ray diffraction. The overall folding of the Glu301Ala FNR mutant shows no significant differences with respect to that of the wild-type enzyme. However, interesting conformational changes are detected in the side chain of another glutamate residue, Glu139, which now points towards the FAD cofactor in the active center cavity. The new conformation of the Glu139 side chain is stabilized by a network of five hydrogen bonds to several water molecules, which seem to hold the carboxylate side chain in a rather fixed position. This interacting network connects the Glu139 side chain to the Ser80 side chain through a series of three water molecules. These observations are discussed in terms of the reactivity of Glu301Ala ferredoxin-NADP+ reductase towards its substrates, and the role of Glu301 in the catalysis is re-examined. Moreover, a structural explanation of the different reoxidation properties of this mutant is given on the basis of the reported structure by modeling the hypothetical flavin C(4a)-hydroperoxide intermediate. The model shows that the distal oxygen of the peroxide anion could be in an appropriate situation to act as the proton donor in the reoxidation process.
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PMID:Structural basis of the catalytic role of Glu301 in Anabaena PCC 7119 ferredoxin-NADP+ reductase revealed by x-ray crystallography. 1065 Oct 39

This study compared the marginal microleakage of Class V cavities restored with Dyract-AP and F2000. Forty Class V cavity preparations were performed on extracted human teeth. As a negative control, twenty teeth were used without Class V preparations. The apical foramina of the teeth were sealed with a layer of varnish and amalgam restorations. Class V cavity preparations with occlusal margins in enamel, and gingival margins in cementum or dentin that measured approximately three millimeters in width (gingival-occlusal) and length (mesial-distal), were prepared on the buccal surface of the teeth. Samples were divided randomly into 2 groups of 15, and restored per manufacturer's instructions using experimental primer/conditioner (PCC, D/C) and Single Bond Adhesive (3M). All restorations were polished with an abrasive finishing kit. After storage in 37 degrees C water for 24 hours, all specimens were thermocycled between 5 degrees C and 55 degrees C for 500 cycles with a 30-second dwell time, followed by immersion in 0.2% basic fucsine for 24 hours. Teeth were then embedded in cold cure acrylic resin, sectioned longitudinally, and the dye penetration at the enamel and cementum margins were scored at 30x magnification. Evaluations were rated from 0 to 3 (0 = no leakage; 1 = dye penetration up to one-half of the preparation depth; 2 = dye penetration more than one-half preparation depth, but less than the axial wall; 3 = dye penetration along the axial wall). Both F-2000 and Dyract-AP indicated no leakage in the enamel margins. Dyract-AP showed no leakage at either the enamel or dentin margins. Fisher's Exact Test revealed that this difference in dentin margins was statistically significant (p < 0.05). Under the given conditions, Dyract-AP and F-2000 demonstrated resistance to microleakage in enamel, and showed Dyract-AP to be more resistant to microleakage in dentin than F-2000.
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PMID:Microleakage of Class V restorations using two different compomer systems: an in vitro study. 1082 60

Recent models for water oxidation in photosystem II postulate that the tyrosine Y(Z) radical, Y(Z)(*), abstracts both an electron and a proton from the Mn cluster during one or more steps in the catalytic cycle. This coupling of proton- and electron-transfer events is postulated to provide the necessary driving force for oxidizing the Mn cluster in its higher oxidation states. The formation of Y(Z)(*) requires the deprotonation of Y(Z) by His190 of the D1 polypeptide. For Y(Z)(*) to abstract both an electron and a proton from the Mn cluster, the proton abstracted from Y(Z) must be transferred rapidly from D1-His190 to the lumenal surface via one or more proton-transfer pathways. The proton acceptor for D1-His190 has been proposed to be either Glu189 of the D1 polypeptide or a group positioned by this residue. To further define the role of D1-Glu189, 17 D1-Glu189 mutations were constructed in the cyanobacterium Synechocystis sp. PCC 6803. Several of these mutants are of particular interest because they appear to assemble Mn clusters in 70-80% of reaction centers in vivo, but evolve no O(2). The EPR and electron-transfer properties of PSII particles isolated from the D1-E189Q, D1-E189L, D1-E189D, D1-E189N, D1-E189H, D1-E189G, and D1-E189S mutants were examined. Intact PSII particles isolated from mutants that evolved no O(2) also exhibited no S(1) or S(2) state multiline EPR signals and were unable to advance beyond an altered Y(Z)(*)S(2) state, as shown by the accumulation of narrow "split" EPR signals under multiple turnover conditions. In the D1-E189G and D1-E189S mutants, the quantum yield for oxidizing the S(1) state Mn cluster was very low, corresponding to a > or =1400-fold slowing of the rate of Mn oxidation by Y(Z)(*). In Mn-depleted D1-Glu189 mutant PSII particles, charge recombination between Q(A)(*)(-) and Y(Z)(*) in the mutants was accelerated, showing that the mutations alter the redox properties of Y(Z) in addition to those of the Mn cluster. These results are consistent with D1-Glu189 participating in a network of hydrogen bonds that modulates the properties of both Y(Z) and the Mn cluster and are consistent with proposals that D1-Glu189 positions a group that accepts a proton from D1-His190.
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PMID:Glutamate 189 of the D1 polypeptide modulates the magnetic and redox properties of the manganese cluster and tyrosine Y(Z) in photosystem II. 1082 40

We report here that osmotic effects and ionic effects are both involved in the NaCl-induced inactivation of the photosynthetic machinery in the cyanobacterium Synechococcus sp. PCC 7942. Incubation of the cyanobacterial cells in 0.5 M NaCl induced a rapid and reversible decline and subsequent slow and irreversible loss of the oxygen-evolving activity of photosystem (PS) II and the electron transport activity of PSI. An Na(+)-channel blocker protected both PSII and PSI against the slow, but not the rapid, inactivation. The rapid decline resembled the effect of 1.0 M sorbitol. The presence of both an Na(+)-channel blocker and a water-channel blocker protected PSI and PSII against the short- and long-term effects of NaCl. Salt stress also decreased cytoplasmic volume and this effect was enhanced by the Na(+)-channel blocker. Our observations suggested that NaCl had both osmotic and ionic effects. The osmotic effect decreased the amount of water in the cytosol, rapidly increasing the intracellular concentration of salts. The ionic effect was caused by an influx of Na(+) ions through potassium/Na(+) channels that also increased concentrations of salts in the cytosol and irreversibly inactivated PSI and PSII.
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PMID:Ionic and osmotic effects of NaCl-induced inactivation of photosystems I and II in Synechococcus sp. 1088 54

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

Replacement of the axial histidine ligand with exogenous imidazole has been accomplished in a number of heme protein mutants, where it often serves to complement the functional properties of the protein. In this paper, we describe the effects of pH and buffer ion on the crystal structure of the H175G mutant of cytochrome c peroxidase, in which the histidine tether between the heme and the protein backbone is replaced by bound imidazole. The structures show that imidazole can occupy the proximal H175G cavity under a number of experimental conditions, but that the details of the interaction with the protein and the coordination to the heme are markedly dependent on conditions. Replacement of the tethered histidine ligand with imidazole permits the heme to shift slightly in its pocket, allowing it to adopt either a planar or distally domed conformation. H175G crystallized from both high phosphate and imidazole concentrations exists as a novel, 5-coordinate phosphate bound state, in which the proximal imidazole is dissociated and the distal phosphate is coordinated to the iron. To accommodate this bound phosphate, the side chains of His-52 and Asn-82 alter their positions and a significant conformational change in the surrounding protein backbone occurs. In the absence of phosphate, imidazole binds to the proximal H175G cavity in a pH-dependent fashion. At pH 7, imidazole is directly coordinated to the heme (d(Fe--Im) = 2.0 A) with a nearby distal water (d(Fe--HOH) = 2.4 A). This is similar to the structure of WT CCP except that the iron lies closer in the heme plane, and the hydrogen bond between imidazole and Asp-235 (d(Im--Asp) = 3.1 A) is longer than for WT CCP (d(His--Asp) = 2.9 A). As the pH is dropped to 5, imidazole dissociates from the heme (d(Fe--Im) = 2.9 A), but remains in the proximal cavity where it is strongly hydrogen bonded to Asp-235 (d(Im--Asp) = 2.8 A). In addition, the heme is significantly domed toward the distal pocket where it may coordinate a water molecule. Finally, the structure of H175G/Im, pH 6, at low temperature (100 K) is very similar to that at room temperature, except that the water above the distal heme face is not present. This study concludes that steric restrictions imposed by the covalently tethered histidine restrain the heme and its ligand coordination from distortions that would arise in the absence of the restricted tether. Coupled with the functional and spectroscopic properties described in the following paper in this issue, these structures help to illustrate how the delicate and critical interactions between protein, ligand, and metal modulate the function of heme enzymes.
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PMID:Replacement of the axial histidine ligand with imidazole in cytochrome c peroxidase. 1. Effects on structure. 1117 Apr 52

The psbX gene (sml0002) coding for a 4.1 kDa protein in Photosystem II of plants and cyanobacteria was deleted in both wild type and in a Photosystem I-less mutant of the cyanobacterium Synechocystis sp. PCC 6803. Polymerase chain reaction and sequencing analysis showed that the mutants had completely segregated. Deletion of the PsbX protein does not seem to influence growth rate, electron transport or water oxidation ability. Whereas a high light induction of the psbX mRNA could be observed in wild type, deletion of the gene did not lead to high light sensibility. Light saturation measurements and 77K fluorescence measurements indicated a minor disconnection of the antenna in the deletion mutant. Furthermore, fluorescence induction measurements as well as immuno-staining of the D1 protein showed that the amount of Photosystem II complexes in the mutants was reduced by 30%. Therefore, PsbX does not seem to be necessary for the Photosystem II electron transport, but directly or indirectly involved in the regulation of the amount of functionally active Photosystem II centres in Synechocystis sp. PCC 6803.
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PMID:Functional analysis of the PsbX protein by deletion of the corresponding gene in Synechocystis sp. PCC 6803. 1120 42


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