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1.
Constant Phycobilisome Size in Chromatically Adapted Cells of the Cyanobacterium Tolypothrix tenuis, and Variation in Nostoc sp
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Phycobilisomes of Tolypothrix tenuis, a cyanobacterium capable of complete chromatic adaptation, were studied from cells grown in red and green light, and in darkness. The phycobilisome size remained constant irrespective of the light quality. The hemidiscoidal phycobilisomes had an average diameter of about 52 nanometers and height of about 33 nanometers, by negative staining. The thickness was equivalent to a phycocyanin molecule (about 10 nanometers). The molar ratio of allophycocyanin, relative to other phycobiliproteins always remained at about 1:3. Phycobilisomes from red light grown cells and cells grown heterotrophically in darkness were indistinguishable in their pigment composition, polypeptide pattern, and size. Eight polypeptides were resolved in the phycobilin region (17.5 to 23.5 kilodaltons) by isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Half of these were invariable, while others were variable in green and red light. It is inferred that phycoerythrin synthesis in green light resulted in a one for one substitution of phycocyanin, thus retaining a constant phycobilisome size. Tolypothrix appears to be one of the best examples of phycobiliprotein regulation with wavelength. By contrast, in Nostoc sp., the decrease in phycoerythrin in red light cells was accompanied by a decrease in phycobilisome size but not a regulated substitution. 相似文献
2.
Further evidence for a phycobilisome model from selective dissociation, fluorescence emission, immunoprecipitation, and electron microscopy. 总被引:8,自引:0,他引:8
Phycobilisomes, isolated in 500 mM Sorensen's phosphate buffer pH 6.8 from the red alga, Porphyridium cruetum, were analyzed by selective dissociation at various phosphate concentrations. The results are consistent with a structural model consisting of an allophycocyanin core, surrounding by a hemispherical layer of R-phycocyanin, with phycoerythrin being on the periphery. Such a structure also allows maximum energy transfer. Intact phycobilisomes transfer excitation energy ultimately to a pigment with a fluorescence emission maximum at 675 nm. This pigment is presumed to be allophycocyanin in an aggreagated state. Uncoupling of energy transfer among the pigments, and physical release of the phycobiliproteins from the phycobilisome follow a parallel time-course; phycoerythrin is released first, followed by R-phycocyanin, and then allophycocyanin. In 55 mM phosphate buffer, the times at which 50% of each phycobiliprotein has dissociated are: phycoerythrin 40 min, R-phycocyanin 75 min, and allophycocyanin 140 min. The proposed arrangement of phycobiliproteins within phycobilisomes is also consistent with the results from precipitation reactions with monospecific antisera on intact and dissociated phycobilisomes. Anti-phycoertythrin reacts almost immediately with intact phycobilisomes, but reactivity with anti-R-phycocyanin and anti-allophycocyanin is considerably delayed, suggesting that the antigens are not accessible until a loosening of the phycobilsome structure occurs. Reaction wbilisomes, but is much more rapid in phycobilisomes of Nostoc sp. which contains 6-8 times more allophycocyanin. It is proposed that allophycocyanin is partially exposed on the base of isolated intact phycobilisomes of both algae, but that in P. cruentum there are too few accessible sites to permit a rapid formation of a precipitate with anti-allophyocyanin. 相似文献
3.
Phycobilisomes, isolated in 500 mM Sorensen's phosphate buffer pH 6.8 from the red alga, Porphyridium cruentum, were analyzed by selective dissociation at various phosphate concentrations. The results are consistent with a structural model consisting of an allophycocyanin core, surrounded by a hemispherical layer of R-phycocyanin, with phycoerythrin being on the periphery. Such a structure also allows maximum energy transfer.Intact phycobilisomes transfer excitation energy ultimately to a pigment with a fluorescence emission maximum at 675 nm. This pigment is presumed to be allophycocyanin in an aggregated state. Uncoupling of energy transfer among the pigments, and physical release of the phycobiliproteins from the phycobilisome follow a parallel time-course; phycoerythrin is released first, followed by R-phycocyanin, and then allophycocyanin. In 55 mM phosphate buffer, the times at which 50% of each phycobiliprotein has dissociated are: phycoerythrin 40 min, R-phycocyanin 75 min, and allophycocyanin 140 min.The proposed arrangement of phycobiliproteins within phycobilisomes is also consistent with the results from precipitation reactions with monospecific antisera on intact and dissociated phycobilisomes. Anti-phycoerythrin reacts almost immediately with intact phycobilisomes, but reactivity with anti-R-phycocyanin and anti-allophycocyanin is considerably delayed, suggesting that the antigens are not accessible until a loosening of the phycobilisome structure occurs. Reaction with anti-allophycocyanin is very slow in P. cruentum phycobilisomes, but is much more rapid in phycobilisomes of Nostoc sp. which contains 6–8 times more allophycocyanin. It is proposed that allophycocyanin is partially exposed on the base of isolated intact phycobilisomes of both algae, but that in P. cruentum there are too few accessible sites to permit a rapid formation of a precipitate with anti-allophyocyanin.Phycobilisome dissociation is inversely proportional to phosphate concentration (500 mM to 2 mM), and is essentially unaffected by protein concentration in the range used (30–200 μg/ml). Phycobiliprotein release occurs in the same order (phycoerythrin > R-phycocyanin > allophycocyanin) in the pH range 5.4–8.0. 相似文献
4.
Dinitrogen fixation in the world's oceans 总被引:24,自引:1,他引:23
Karl D. Michaels A. Bergman B. Capone D. Carpenter E. Letelier R. Lipschultz F. Paerl H. Sigman D. Stal L. 《Biogeochemistry》2002,(1):47-98
The surface water of themarine environment has traditionally beenviewed as a nitrogen (N) limited habitat, andthis has guided the development of conceptualbiogeochemical models focusing largely on thereservoir of nitrate as the critical source ofN to sustain primary productivity. However,selected groups of Bacteria, includingcyanobacteria, and Archaea canutilize dinitrogen (N2) as an alternativeN source. In the marine environment, thesemicroorganisms can have profound effects on netcommunity production processes and can impactthe coupling of C-N-P cycles as well as the netoceanic sequestration of atmospheric carbondioxide. As one component of an integrated Nitrogen Transport and Transformations project, we have begun to re-assess ourunderstanding of (1) the biotic sources andrates of N2 fixation in the world'soceans, (2) the major controls on rates ofoceanic N2 fixation, (3) the significanceof this N2 fixation for the global carboncycle and (4) the role of human activities inthe alteration of oceanic N2 fixation. Preliminary results indicate that rates ofN2 fixation, especially in subtropical andtropical open ocean habitats, have a major rolein the global marine N budget. Iron (Fe)bioavailability appears to be an importantcontrol and is, therefore, critical inextrapolation to global rates of N2fixation. Anthropogenic perturbations mayalter N2 fixation in coastal environmentsthrough habitat destruction and eutrophication,and open ocean N2 fixation may be enhancedby warming and increased stratification of theupper water column. Global anthropogenic andclimatic changes may also affect N2fixation rates, for example by altering dustinputs (i.e. Fe) or by expansion ofsubtropical boundaries. Some recent estimatesof global ocean N2 fixation are in therange of 100–200 Tg N (1–2 × 1014 g N)yr–1, but have large uncertainties. Theseestimates are nearly an order of magnitudegreater than historical, pre-1980 estimates,but approach modern estimates of oceanicdenitrification. 相似文献
5.
1 NSec molecular dynamics (MD) simulation of anti-hen egg white antibody, HyHEL63 (HH63), complexed with HEL reveals important
molecular interactions, not revealed in its X-ray crystal structure. These molecular interactions were predicted to be critical
for the complex formation, based on structure–function studies of this complex and 3-other anti-HEL antibodies, HH8, HH10
and HH26, HEL complexes. All four antibodies belong to the same structural family, referred to here as HH10 family. Ala scanning
results show that they recognize ‘coincident epitopes’. 1 NSec explicit, with periodic boundary condition, MD simulation of
HH63-HEL reveals the presence of functionally important salt-bridges. Around 200 ps in vacuo and an additional 20 ps explicit
simulation agree with the observations from 1 Nsec simulation. Intra-molecular salt-bridges predicted to play significant
roles in the complex formation, were revealed during MD simulation. A very stabilizing salt-bridge network, and another intra-molecular
salt-bridge, at the binding site of HEL, revealed during the MD simulation, is proposed to predipose binding site geometry
for specific binding. All the revealed salt-bridges are present in one or more of the other three complexes and/or involve
“hot-spot” epitope and paratope residues. Most of these charged epitope residues make large contribution to the binding free
energy. The “hot spot” epitope residue Lys97Y, which significantly contributes to the free energy of binding in all the complexes, forms an intermolecular salt-bridge
in several MD conformers. Our earlier computations have shown that this inter-molecular salt-bridge plays a significant role
in determining specificity and flexibility of binding in the HH8-HEL and HH26-HEL complexes. Using a robust criterion of salt-bridge
detection, this inter-molecular salt-bridge was detected in the native structures of the HH8-HEL and HH26-HEL complexes, but
was not revealed in the crystal structure of HH63-HEL complex. The electrostatic strength of this revealed salt-bridge was
very strong. During 1 Nsec MD simulation this salt-bridge networks with another inter-molecular salt-bridge to form an inter-molecular
salt-bridge triad. Participation of Lys97Y in the formation of inter-molecular triad further validates the functional importance of Lys97Y in HH63-HEL associations. These results demonstrate that many important structural details of biomolecular interactions can
be better understood when studied in a dynamic environment, and that MD simulations can complement and expand information
obtained from static X-ray structure. This study also highlights “hot-spot” molecular interactions in HyHEL63-HEL complex.
The publisher or recipient acknowledges right of the U.S. Government to retain a non exclusive, royalty-free license in and
to any copyright covering the article. 相似文献
6.
An assessment of nitrogen fixation as a source of nitrogen to the North Atlantic Ocean 总被引:2,自引:2,他引:0
The role of nitrogen fixation in the nitrogen cycle of the North Atlantic basin was re-evaluated because recent estimates had indicated a far higher rate than previous reports. Examination of the available data on nitrogen fixation rates and abundance ofTrichodesmium, the major nitrogen fixing organism, leads to the conclusion that rates might be as high as 1.09 × 1012 mol N yr–1. Several geochemical arguments are reviewed that each require a large nitrogen source that is consistent with nitrogen fixation, but the current data, although limited, do not support a sufficiently high rate. However, recent measurements of the fixation rates per colony are higher than the historical average, suggesting that improved methodology may require a re-evaluation through further measurements. The paucity of temporally resolved data on both rates and abundance for the major areal extent of the tropical Atlantic, where aeolian inputs of iron may foster high fixation rates, represents another major gap. 相似文献
7.
BIOLOGICAL AND CHEMICAL CHARACTERISTICS OF THE GIANT DIATOM ETHMODISCUS (BACILLARIOPHYCEAE) IN THE CENTRAL NORTH PACIFIC GYRE 总被引:1,自引:0,他引:1
Tracy A. Villareal Leanne Joseph Mark A. Brzezinski Rebecca F. Shipe Fredric Lipschultz Mark A. Altabet 《Journal of phycology》1999,35(5):896-902
Cells of the giant diatom Ethmodiscus Castr. gathered from the upper 15 m were examined for O2 evolution, nitrate reductase activity (NRA), C and N composition, internal NO concentrations, , and 15NO, 15NH , and 32Si uptake in a series of cruises in the central N. Pacific gyre. The δ15N (2.56–5.09 ‰), internal NO concentrations (0.0– 11.5 mM NO−), and NRA (6.7 ± 4.7 × 10−4μM NO cell −1·h−1) were consistent with recent exposure to elevated nitrate concentrations and utilization of deep NO as a primary N source. These results are similar to other diatoms that migrate vertically to the nutricline as part of their life cycle. Rate measures (Si[OH]4 uptake, NRA, and O2 evolution) indicated surface doubling times from 45 h to 75 h. Both NO and NH uptake in surface waters were low and inadequate to supply N needs at surface NO and NH concentrations. Our results suggest a partitioning in nutrient acquisition, with N acquired at depth and C and Si acquired at the surface. Doubling rates were two to three times higher than predicted from cell volume and C content models. These data are consistent with the observed elemental content being lower than expected because of the dominance of cell volume by the vacuole. Our calculations suggest that Ethmodiscus contributes little to the biogeochemistry of the upper water column via upward nutrient transport. Although reported as a paleo-upwelling indicator, thisevidence suggests that Ethmodiscus has adapted to the nutrient-poor open ocean by a vertical migration strategy and has biological characteristics inconsistent with a upwelling indicator. 相似文献
8.
Serial sections of uncorticated axial cells of Compsopogon coeruleus revealed a single interconnected parietal chloroplast. Phycobilisomes in such chloroplasts were hemidiscoidal in shape with a broad-face diameter of ca. 25–30 nm. The molar ratio of phycobiliproteins in whole cell extracts was IPE:3PC:1APC, similar to isolated phycobilisomes. Two spectrally distinct C-phycocyanin forms (A618 nm, F648 nm and A630 nm, F652 nm) were resolved in dissociated phycobilisomes along with B-phycoerythrin and allophycocyanin. 相似文献
9.
Phycobilisomes of Porphyridium cruentum: pigment analysis 总被引:13,自引:0,他引:13
10.
Matthew?M.?MillsEmail author Fredric?Lipschultz Kenneth?P.?Sebens 《Coral reefs (Online)》2004,23(3):311-323
The ingestion of two size classes of natural particulate matter (PM) and the uptake of the associated nitrogen by four species of scleractinian corals was measured using the stable isotopic tracer 15N. PM collected in sediment traps was split into <63 and >105 µm size fractions and labeled with (15N-NH4)2SO4. Siderastrea radians,
Montastrea franksi, Diploria strigosa, and Madracis mirabilis
were incubated in flow chambers with the labeled PM in suspension (<63 µm), or deposited onto coral surfaces (>105 µm). Ingestion was detected for all four species (98–600 µg Dry wt. cm–2 h–1), but only for D. strigosa was any difference detected between suspended and deposited PM. Only the three mounding species, S. radians, M. franksi, and D. strigosa showed uptake of suspended and deposited particulate nitrogen (PN); whereas, the branched coral M. mirabilis had no measurable PN uptake. Only coral host tissues were enriched with 15N, with no tracer detected in the symbiotic zooxanthellae. Uptake rates ranged from as low as 0.80 µg PN cm–2 h–1 in S. radians to as high as 13 µg PN cm–2 h–1 in M. franksi. M. franksi had significantly higher uptake rates than S. radians (ANOVA,
p<0.05), while D. strigosa had a statistically similar uptake rate compared to both species. These results are the first to compare scleractinian ingestion of nitrogen associated with suspended and deposited particulate matter, and demonstrate that the use of PM as a nitrogen source varies with species and colony morphology. 相似文献