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

The freshwater cyanobacterium Synechococcus PCC 6311 is able to adapt to grow after sudden exposure to salt (NaCl) stress. We have investigated the mechanism of Na+ transport in these cells during adaptation to high salinity. Na+ influx under dark aerobic conditions occurred independently of delta pH or delta psi across the cytoplasmic membrane, ATPase activity, and respiratory electron transport. These findings are consistent with the existence of Na+/monovalent anion cotransport or simultaneous Na+/H(+)+anion/OH- exchange. Na+ influx was dependent on Cl-, Br-, NO3-, or NO2-. No Na+ uptake occurred after addition of NaI, NaHCO3, or Na2SO4. Na+ extrusion was absolutely dependent on delta pH and on an ATPase activity and/or on respiratory electron transport. This indicates that Na+ extrusion via Na+/H+ exchange is driven by primary H+ pumps in the cytoplasmic membrane. Cells grown for 4 days in 0.5 M NaCl medium, "salt-grown cells," differ from control cells by a lower vmax of Na+ influx and by lower steady-state ratios of [Na+]in/[Na+]out. These results indicate that cells grown in high-salt medium increase their capacity to extrude Na+. During salt adaptation Na+ extrusion driven by respiratory electron transport increased from about 15 to 50%.
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PMID:NMR studies on Na+ transport in Synechococcus PCC 6311. 131 38

Photosystem I catalyzes the light-driven oxidation of plastocyanin or cytochrome c6 and the reduction of ferredoxin or flavodoxin. PsaJ is a 4.4 kDa hydrophobic subunit of photosystem I from cyanobacteria and chloroplasts. To investigate the function of PsaJ, we generated a mutant strain of the cyanobacterium Synechocystis sp. PCC 6803 in which the psaJ gene is replaced by a gene for chloramphenicol resistance. Deletion of psaJ led to a reduction in the steady state RNA level from psaF which is located upstream from psaJ. Immunoquantification using an anti-PsaF antibody revealed a significant decrease in the amount of PsaF in membranes of the mutant strain. Trimeric photosystem I complexes isolated from the mutant strain using n-dodecyl beta-D-maltoside lacked PsaJ, contained ca. 80% less PsaF, but maintained wild-type levels of other photosystem I subunits. In contrast, the photosystem I purified using Triton X-100 contained less than 2% PsaF when compared to the wild type, showing the more extractable nature of PsaF in PsaJ-less photosystem I in the presence of Triton X-100. PsaE was more accessible to removal by NaI in a mutant strain lacking PsaF and PsaJ than in the wild type. The presence of PsaF in photosystem I from the PsaJ-less strain did not alter the increased susceptibility of PsaE to removal by NaI. These results indicate an interaction between PsaJ and PsaF in the organization of the complex.
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PMID:Targeted deletion of psaJ from the cyanobacterium Synechocystis sp. PCC 6803 indicates structural interactions between the PsaJ and PsaF subunits of photosystem I. 752 26

Photosystem I functions as a light-driven plastocyanin-ferredoxin oxidoreductase in the photosynthetic membranes of cyanobacteria and chloroplasts. A mutant strain of the cyanobacterium Synechocystis sp. PCC 6803 that contains a deletion of the psaF gene and a transcriptionally inactive psaJ gene has assembled photosystem I complexes that lack PsaF, a lumenal protein and PsaJ, a 4-kDa hydrophobic protein. The cells of the mutant and wild type strains have similar rates of photosynthetic electron transfer and P700+ rereduction under linear and cyclic electron transfer conditions. Analysis of flash-induced absorption transients at 700 nm demonstrate that the absence of PsaF in purified mutant photosystem I did not affect the rate of P700 rereduction by cytochrome c553. Therefore, PsaF is not essential for docking of cytochrome c553. We also studied the organization of the proteins of mutant and wild type photosystem I by comparing their accessibility to digestion by thermolysin or to removal by 1 M NaI. The PsaA-PsaB subunits were more easily degraded by thermolysin in the mutant photosystem I. Thermolysin cleavage of PsaB yielded two major fragments that were immunoreactive with an antibody raised against the C terminus of PsaB. The N termini of these PsaB peptides mapped at Ile482 and Ile498 residues, thus identifying a surface-exposed domain of the core of photosystem I. The PsaE subunit could be removed by 1 M NaI and was rapidly digested by thermolysin in the mutant but not in the wild type photosystem I. Therefore, PsaF and PsaJ subunits of photosystem I have dispensable accessory roles in the function and organization of the complex.
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PMID:Function and organization of photosystem I in a cyanobacterial mutant strain that lacks PsaF and PsaJ subunits. 810 55

PsaA and PsaB are homologous integral membrane proteins that form the heterodimeric core of photosystem I. Domain-specific antibodies were generated to examine the topography of PsaA and PsaB. The purified photosystem I complexes from the wild type strain of Synechocystis sp. PCC 6803 were treated with eight proteases to study the accessibility of cleavage sites in PsaA and PsaB. Proteolytic fragments were identified using the information from N-terminal amino acid sequencing, reactivity to antibodies, apparent mass, and specificity of proteases. The extramembrane loops of PsaA and PsaB differed in their accessibility to proteases, which indicated the folded structure of the loops or their shielding by the small subunits of photosystem I. NaI-treated and mutant photosystem I complexes were used to identify the extramembrane loops that were exposed in the absence of specific small subunits. The absence of PsaD exposed additional proteolytic sites in PsaB, whereas the absence of PsaE exposed sites in PsaA. These studies distinguish PsaA and PsaB in the structural model for photosystem I that has been proposed on the basis of x-ray diffraction studies (Krauss, N., Schubert, W.-D., Klukas, O., Fromme, P., Witt, H. T., and Saenger, W. (1996) Nat. Struct. Biol. 3, 965-973). Using osmotically shocked cells for protease treatments, the N terminus of PsaA was determined to be on the n side of the photosynthetic membranes. Based on these data and available published information, we propose a topological model for PsaA and PsaB.
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PMID:Topography of the photosystem I core proteins of the cyanobacterium Synechocystis sp. PCC 6803. 926 9

The PsaD subunit of photosystem I (PSI) is a peripheral protein that provides a docking site for ferredoxin and interacts with the PsaB, PsaC, and PsaL subunits of PSI. We used site-directed mutagenesis to determine the function of a basic region in PsaD of the cyanobacterium Synechocystis sp. PCC 6803. We generated five mutant strains in which one or more charged residues were altered. Western blotting showed that replacement of lysine (Lys)-74 with glutamine or glutamic acid led to a substantial decrease in the level of PsaD in the membranes. The mutant PSI complexes showed reduced NADP+ photoreduction activity mediated by ferredoxin; the decrease in activity correlated with the reduced level of PsaD. Using protein synthesis inhibitors we showed that the degradation rates of the mutant and wild-type PsaD were similar, indicating a defect in the assembly of the mutant protein. Treatment of the mutant PSI complexes with a different concentration of NaI showed that the mutations decreased affinity between PsaD and the transmembrane components of PSI. With glutaraldehyde, the mutant and wild-type PsaD proteins could be cross-linked with PsaC, but the PsaD-PsaL cross-linked product was reduced drastically when arginine-72, Lys-74, and Lys-76 were mutated simultaneously. These studies demonstrate that the basic residues in the central region of PsaD, especially Lys-74, are crucial in the assembly of PsaD into the PSI complex.
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PMID:The PsaD subunit of photosystem I. Mutations in the basic domain reduce the level of PsaD in the membranes. 941 69

An alpha-carbonyl radical cyclization approach toward synthesis of angular triquinanes is described. As a model study, conjugate addition of 4-(trimethylsilyl)-3-butynylmagnesium chloride to enone 7 followed by trapping of the enolate with chlorotrimethylsilane gave trimethysilyl enol ether 8. Iodination of 8 with a mixture of NaI and m-CPBA afforded iodo ketone 6. Radical cyclization of 6 effected by Bu(3)SnH and AIBN gave 5. Epoxidation of 5 with m-CPBA yielded epoxy ketone 9. Desilylation and rearrangement of 9 by formic acid gave aldehyde 4. Aldol condensation and dehydration furnished angular triquinane skeleton 3. Total synthesis of (-)-5-oxosilphiperfol-6-ene (1) was accomplished in 12 steps starting from keto ester 14 based on this route. Conjugate addition of 3-hexynylmagnesium bromide to chiral ester 13 followed by treatment with chlorotrimethylsilane gave intermediate 15. Iodination of 15 with a mixture of NaI and m-CPBA gave alpha-iodo ester 12. Intramolecular radical cyclization of 12 gave ester 11. Reduction of 11 by LiAlH(4) yielded alcohol 16. On treatment with m-CPBA, alcohol 16 was converted to the corresponding epoxide 17, which was subjected to the epoxy-ketone rearrangement using BF(3) etherate as a catalyst to give ethyl ketone 18. Subsequent oxidation of 18 with PCC afforded aldehyde 10. Intramolecular aldol condensation of 10 yielded tricyclic compound 19. Methylation of 19 gave 20. Conjugate addition of lithium dimethylcuprate to 20 followed by trapping of the resulting enolate with chlorotrimethylsilane gave 21. Oxidation of 21 by DDQ afforded enantiomerically pure (-)-5-oxosilphiperfol-6-ene (1). Racemic (+/-)-1was also synthesized in the same manner in order to determine the optical purity of chiral product (-)-1. The gas chromatographic analysis with a chiral column proved that 1 has high enantiomeric purity. A single-crystal X-ray analysis of 2,4-dinitrophenylhydrazone 22 was performed to unambiguously confirm the stereochemistry of 19.
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PMID:alpha-Carbonyl Radical Cyclization Approach toward Angular Triquinanes: Total Synthesis of Enantiomerically Pure (-)-5-Oxosilphiperfol-6-ene. 1167 39

The wild-type, PsaD-less, and PsaL-less strains of the cyanobacterium Synechocystis sp. PCC 6803 were used to study subunit interactions in photosystem I (PSI). When the membranes of a PsaD-less strain were solubilized with Triton X-100 and PSI was purified using ion-exchange chromatography and sucrose-gradient ultracentrifugation, the PsaL subunit was substantially removed from the core of PSI, whereas other subunits, such as PsaE and PsaF, were quantitatively retained during purification. When the wild-type PSI was exposed to increasing concentrations of NaI, the PsaE, PsaD, and PsaC subunits were gradually removed, whereas PsaF, PsaL, PsaK, and PsaJ resisted removal by up to 3 M NaI. The absence of PsaL enhanced the accessibility of PsaD to removal by NaI. Treatment of the wild-type PSI complexes with glutaraldehyde at 4[deg] C resulted in a 29-kD cross-linked product between PsaD and PsaL. The formation of such cross-linked species was independent of PSI concentrations, suggesting an intracomplex cross-linking between PsaD and PsaL. Taken together, these results demonstrate a structural interaction between PsaD and PsaL that plays a role in their association with the PSI core.
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PMID:Organization of Photosystem I Polypeptides (A Structural Interaction between the PsaD and PsaL Subunits). 1223 86