| 51. |
- Rojdestvenski, I, et al.
(författare)
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A carbonic anhydrase catalyzed CO2 pump in Chlamydomonas reinhardtii : In vivo experiments, computer modelling, and theory
- 2000
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Ingår i: Russian journal of plant physiology. - 1021-4437 .- 1608-3407. ; 47:5, s. 613-621
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Tidskriftsartikel (refereegranskat)abstract
- We studied the bicarbonate depletion effects on photosynthesis in high-CO2 grown-cell wall-less mutants of Chlamydomonas reinhardtii with (cw92) and without (cia3/cw15) active carbonic anhydrase (CA) associated with photosystem II (PSII). The mutants were grown in a high-CO2 medium and then washed with a CO2-free buffer. We discuss the shutdown of oxygen evolution in cw92 as a consequence of CO2 depletion of the Calvin cycle. It is suggested that CA acts as part of a PSII-driven pump delivering CO2 from the lumen into the stroma, where it becomes available to the Calvin cycle. Our model is supported by computer simulation data and accommodates the results of in vivo experiments as well as the differences between cw92 and cia3 mutants. We also present a simple theory of the phenomena discussed, based on a time-scale hierarchy approach, which describes the CO2 depletion in cw92 using only two rate constants-V-max and K-m of the Calvin cycle.
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| 52. |
- Rouhier, Nicolas, et al.
(författare)
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Identification of plant glutaredoxin targets
- 2005
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Ingår i: Antioxidants and Redox Signaling. - Larchmont, NY : Mary Ann Liebert. - 1523-0864 .- 1557-7716. ; 7:7-8, s. 919-929
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Tidskriftsartikel (refereegranskat)abstract
- Glutaredoxins (Grxs) are small ubiquitous proteins of the thioredoxin (Trx) family, which catalyze dithiol–disulfide exchange reactions or reduce protein-mixed glutathione disulfides. In plants, several Trx-interacting proteins have been isolated from different compartments, whereas very few Grx-interacting proteins are known. We describe here the determination of Grx target proteins using a mutated poplar Grx, various tissular and subcellular plant extracts, and liquid chromatography coupled to tandem mass spectrometry detection. We have identified 94 putative targets, involved in many processes, including oxidative stress response [peroxiredoxins (Prxs), ascorbate peroxidase, catalase], nitrogen, sulfur, and carbon metabolisms (methionine synthase, alanine aminotransferase, phosphoglycerate kinase), translation (elongation factors E and Tu), or protein folding (heat shock protein 70). Some of these proteins were previously found to interact with Trx or to be glutathiolated in other organisms, but others could be more specific partners of Grx. To substantiate further these data, Grx was shown to support catalysis of the stroma β-type carbonic anhydrase and Prx IIF of Arabidopsis thaliana, but not of poplar 2-Cys Prx. Overall, these data suggest that the interaction could occur randomly either with exposed cysteinyl disulfide bonds formed within or between target proteins or with mixed disulfides between a protein thiol and glutathione.
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| 53. |
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| 54. |
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| 55. |
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| 56. |
- Samuelsson, Göran, 1951-
(författare)
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The use of fluorescence techniques for the study of some membrane-bound photosynthetic properties and some effects of copper on the thylakoid membrane
- 1981
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lyophilized pea chloroplasts were extracted in a stepwise manner in an organic solvent (petroleum ether) with increasing polarity which was obtained by addition of small amount of ETOH (0-1 %). Absorption and low temperature fluorescence emission spectra were measured on both the extracted thylakoids and on isolated chlorophylI-protein complexes. Extraction of chlorophyll from the membrane increased (and the ratio of chlorophyl l a/b decreased) with increasing polarity of the solvent. The gel scan revealed that after extraction with petroleum ether, CPa.. was lost from the gel and after extraction with petroleum ether +1 % ETOH only the CPa/b was left together with SDS-free chlorophyll. This shows that the chlorophyll in CPa/b are situated in a less hydrophobic environment than chlorophyll in CPa|| and CPa|. The long wavelength absorbing and emitting chlorophyll fraction associated to CPaj was found to be easily removed from the membrane. This caused a blue shift in the low temperature fluorescence emission peak and in the red absorption peak and it was also accompanied by a decrease in carote-noid absorption in isolated CPa|. It was found in different plant material lacking $-carotene in CPàj that a strong correlation between ß-carotene in CPa. and the existence of the long wavelength chlorophyll in isolated cPa. existed. Based on these data, it was suggested that excited chlorophyll can transfer energy in excess to ß-carotene by a triplet--triplet transfer.A method based on in vivo chlorophyll £ fluorescence was developed for studying photosynthetic capacity in unicellular algae. It was shown that DCMU-induced fluorescence increase was a good measure of photosynthetic capacity in four species of green algae tested.The effect of copper chloride on photosynthetic electron transport and chlorophyl1-protein complexes was studied in spinach chloroplasts. Copper(11) inhibited a PS I i reaction H2O—> DPIP, a PS I reaction Asc/DPIP —> NADP and the overall electron transport H2O —> NAOP to different degrees. Chlorophyll protein complexes were only slightly affected by copper(ll) but with both copper and ascorbate in the reaction media, a rapid membrane destruction occurred. This was probably caused by a free radical reaction catalyzed by copper(ll).
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| 57. |
- Samuelsson, Ulf, 1951-, et al.
(författare)
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Islet autoantibodies in the prediction of diabetes in school children
- 2001
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Ingår i: Diabetes Research and Clinical Practice. - 1872-8227 .- 0168-8227. ; 51:1, s. 51-57
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Tidskriftsartikel (refereegranskat)abstract
- In 1987 serum was collected from 1031 non-diabetic schoolchildren in the Southeast area of Sweden with the aim of evaluating islet autoantibody status (ICA, GADA and IA2-ab) in the prediction of diabetes in schoolchildren. The clinical development of Type 1 diabetes in the children was assessed in 1994 and 1997. The combination of ICA, GADA and IA2-ab were found in four subjects whereas six had two and 35 children one of these antibodies. After 10 years, six of the 1031 children had developed clinical diabetes and five of these six children were positive for islet antibodies. Two were positive for all three antibodies, two were positive for ICA and GADA, and one was positive for GADA. Among the individual autoantibodies, ICA showed the highest positive predictive value (29%) whereas the predictive value for the combination of two autoantibodies was highest for GADA and ICA (40%). Thus, GADA and ICA measurements may be a rational approach to detect schoolchildren at risk for developing diabetes.
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| 58. |
- Shevela, Dmitriy, et al.
(författare)
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Efficiency of photosynthetic water oxidation at ambient and depleted levels of inorganic carbon
- 2013
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Ingår i: Photosynthesis Research. - : Springer. - 0166-8595 .- 1573-5079. ; 117:1-3, s. 401-412
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Tidskriftsartikel (refereegranskat)abstract
- Over 40 years ago, Joliot et al. (Photochem Photobiol 10:309-329, 1969) designed and employed an elegant and highly sensitive electrochemical technique capable of measuring O2 evolved by photosystem II (PSII) in response to trains of single turn-over light flashes. The measurement and analysis of flash-induced oxygen evolution patterns (FIOPs) has since proven to be a powerful method for probing the turnover efficiency of PSII. Stemler et al. (Proc Natl Acad Sci USA 71(12):4679-4683, 1974), in Govindjee's lab, were the first to study the effect of "bicarbonate" on FIOPs by adding the competitive inhibitor acetate. Here, we extend this earlier work by performing FIOPs experiments at various, strictly controlled inorganic carbon (Ci) levels without addition of any inhibitors. For this, we placed a Joliot-type bare platinum electrode inside a N2-filled glove-box (containing 10-20 ppm CO2) and reduced the Ci concentration simply by washing the samples in Ci-depleted media. FIOPs of spinach thylakoids were recorded either at 20-times reduced levels of Ci or at ambient Ci conditions (390 ppm CO2). Numerical analysis of the FIOPs within an extended Kok model reveals that under Ci-depleted conditions the miss probability is discernibly larger (by 2-3 %) than at ambient conditions, and that the addition of 5 mM HCO3 (-) to the Ci-depleted thylakoids largely restores the original miss parameter. Since a "mild" Ci-depletion procedure was employed, we discuss our data with respect to a possible function of free or weakly bound HCO3 (-) at the water-splitting side of PSII.
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| 59. |
- Shitov, A V, et al.
(författare)
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A carbonic anhydrase inhibitor induces bicarbonate-reversible suppression of electron transfer in pea photosystem 2 membrane fragments
- 2011
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Ingår i: Journal of Photochemistry and Photobiology. B. - : Elsevier. - 1011-1344 .- 1873-2682. ; 104:1-2, s. 366-371
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Tidskriftsartikel (refereegranskat)abstract
- The effects of suppression of the carbonic anhydrase (CA) activity by a CA-inhibitor, acetazolamide (AA), on the photosynthetic activities of photosystem II (PS II) particles from higher plants were investigated. AA along with CA-activity inhibits the PS II photosynthetic electron transfer and the AA-induced suppression is totally reversed by the addition of bicarbonate (3-5 mM). Similar effect of recovery in the PS II photosynthetic activity was also revealed upon the addition of known artificial electron donors (potassium ferrocyanide and TMPD). Significance and possible functions of CA for the PS II donor side are discussed.
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| 60. |
- Shutova, Tatiana, 1964-, et al.
(författare)
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The photosystem II-associated Cah3 in Chlamydomonas enhances the O-2 evolution rate by proton removal
- 2008
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Ingår i: EMBO Journal. - : Wiley. - 0261-4189 .- 1460-2075. ; 27:5, s. 782-791
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Tidskriftsartikel (refereegranskat)abstract
- Water oxidation in photosystem II ( PSII) is still insufficiently understood and is assumed to involve HCO3-. A Chlamydomonas mutant lacking a carbonic anhydrase associated with the PSII donor side shows impaired O-2 evolution in the absence of HCO3-. The O-2 evolution for saturating, continuous illumination (R-O2) was slower than in the wild type, but was elevated by HCO3- and increased further by Cah3. The R-O2 limitation in the absence of Cah3/HCO3- was amplified by H2O/D2O exchange, but relieved by an amphiphilic proton carrier, suggesting a role of Cah3/HCO3- in proton translocation. Chlorophyll fluorescence indicates a Cah3/HCO3- effect at the donor side of PSII. Time-resolved delayed fluorescence and O-2-release measurements suggest specific effects on proton-release steps but not on electron transfer. We propose that Cah3 promotes proton removal from the Mn complex by locally providing HCO3-, which may function as proton carrier. Without Cah3, proton removal could become rate limiting during O-2 formation and thus, limit water oxidation under high light. Our results underlie the general importance of proton release at the donor side of PSII during water oxidation.
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