Deactivation processes in PsbA1-Photosystem II and PsbA3-Photosystem II under photoinhibitory conditions in the cyanobacterium Thermosynechococcus elongatus

AbstractThe sensitivity to high light conditions of Photosystem II with either PsbA1 (WT*1) or PsbA3 (WT*3) as the D1 protein was studied in whole cells of the thermophilic cyanobacterium Thermosynechococcus elongatus. When the cells are cultivated under high light conditions the following results were found: (i) The O2 evolution activity decreases faster in WT*1 cells than in WT*3 cells both in the absence and in the presence of lincomycin, a protein synthesis inhibitor; (ii) In WT*1 cells, the rate constant for the decrease of the O2 evolution activity is comparable in the presence and in the absence of lincomycin; (iii) The D1 content revealed by western blot analysis decays similarly in both WT*1 and WT*3 cells and much slowly than O2 evolution; (iv) The faster decrease in O2 evolution in WT*1 than in WT*3 cells correlates with a much faster inhibition of the S2-state formation; (v) The shape of the WT*1 cells is altered. All these results are in agreement with a photo-inhibition process resulting in the loss of the O2 activity much faster than the D1 turnover in PsbA1-PSII and likely to a greater production of reactive oxygen species under high light conditions in WT*1 than in WT*3. This latter result is discussed in view of the known effects of the PsbA1 to PsbA3 substitution on the redox properties of the Photosystem II cofactors. The observation that under low light conditions WT*3 cells are able to express the psbA3 gene, whereas under similar conditions wild type cells are expressing mainly the psbA1 gene is also discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial

Ycf12 is a core subunit in the photosystem II complex

AbstractThe latest crystallographic model of the cyanobacterial photosystem II (PS II) core complex added one transmembrane low molecular weight (LMW) component to the previous model, suggesting the presence of an unknown transmembrane LMW component in PS II. We have investigated the polypeptide composition in highly purified intact PS II core complexes from Thermosynechococcus elongatus, the species which yielded the PS II crystallographic models described above, to identify the unknown component. Using an electrophoresis system specialized for separation of LMW hydrophobic proteins, a novel protein of ∼5 kDa was identified as a PS II component. Its N-terminal amino acid sequence was identical to that of Ycf12. The corresponding gene is known as one of the ycf (hypothetical chloroplast reading frame) genes, ycf12, and is widely conserved in chloroplast and cyanobacterial genomes. Nonetheless, the localization and function of the gene product have never been assigned. Our finding shows, for the first time, that ycf12 is actually expressed as a component of the PS II complex in the cell, revealing that a previously unidentified transmembrane protein exists in the PS II core complex

Cytochrome c550 in the cyanobacterium Thermosynechococcus elongatus: Study of redox mutants

Cytochrome c550 is one of the extrinsic Photosystem II subunits in cyanobacteria and red algae. To study the possible role of the heme of the cytochrome c550 we constructed two mutants of Thermosynechococcus elongatus in which the residue His-92, the sixth ligand of the heme, was replaced by a Met or a Cys in order to modify the redox properties of the heme. The H92M and H92C mutations changed the midpoint redox potential of the heme in the isolated cytochrome by +125 mV and –30 mV, respectively, compared with the wild type. The binding-induced increase of the redox potential observed in the wild type and the H92C mutant was absent in the H92M mutant. Both modified cytochromes were more easily detachable from the Photosystem II compared with the wild type. The Photosystem II activity in cells was not modified by the mutations suggesting that the redox potential of the cytochrome c550 is not important for Photosystem II activity under normal growth conditions. A mutant lacking the cytochrome c550 was also constructed. It showed a lowered affinity for Cl– and Ca2+ as reported earlier for the cytochrome c550-less Synechocystis 6803 mutant, but it showed a shorter lived Formula state, rather than a stabilized S2 state and rapid deactivation of the enzyme in the dark, which were characteristic of the Synechocystis mutant. It is suggested that the latter effects may be caused by loss (or weaker binding) of the other extrinsic proteins rather than a direct effect of the absence of the cytochrome c55

Analysis of Household Energy Consumption of Lighting and Electric Appliances and Predictions for 2020

increase in household energy consumption has been more apparent than such increases in the industrial and transportation sectors. The sources of household energy consumption can be classified into heating and cooling, cooking, hot-water supply, and lighting and electric appliances. In particular, energy consumption for lighting and electric appliances has been significantly increasing. In order to consider energy-saving measures in the home, we should trace the tendencies of increasing energy consumption due to lighting and electric appliances in recent years. In this paper, we analyze the current level of energy consumption for lighting and electric appliances and, moreover, attempt to predict the level we can expect in 2020. Consequently, it is estimated that the energy consumption of lighting and electric appliances will decrease by 16% from the 2010 level, mainly due to the energy savings expected for refrigerators and lighting

Probing the role of chloride in Photosystem II from Thermosynechococcus elongatus by exchanging chloride for iodide

AbstractThe active site for water oxidation in Photosystem II (PSII) goes through five sequential oxidation states (S0 to S4) before O2 is evolved. It consists of a Mn4CaO5 cluster and TyrZ, a redox-active tyrosine residue. Chloride ions have been known for long time to be required for the function of the enzyme. However, X-ray data have shown that they are located about 7Å away from the Mn4CaO5 cluster, a distance that seems too large to be compatible with a direct involvement of chloride in the water splitting chemistry. We have investigated the role of this anion by substituting I− for Cl− in the cyanobacterium Thermosynechococcus elongatus with either Ca2+ or Sr2+ biosynthetically assembled into the Mn4 cluster. The electron transfer steps affected by the exchanges were investigated by time-resolved UV–visible absorption spectroscopy, time-resolved EPR at room temperature and low temperature cw-EPR spectroscopy. In both Ca-PSII and Sr-PSII, the Cl−/I− exchange considerably slowed down the two S3TyrZ•→(S3TyrZ•)′→S0 reactions in which the fast phase, S3TyrZ•→(S3TyrZ•)′, reflects the electrostatically triggered expulsion of one proton from the catalytic center caused by the positive charge near/on TyrZ• and the slow phase corresponds to the S0 and O2 formations and to a second proton release. The t1/2 for S0 formation increased from 1.1ms in Ca/Cl-PSII to ≈6ms in Ca/I-PSII and from 4.8ms in Sr/Cl-PSII to ≈45ms in Sr/I-PSII. In all cases the TyrZ• reduction was the limiting step. The kinetic effects are interpreted by a model in which the Ca2+ binding site and the Cl− binding site, although spatially distant, interact. This interaction is likely mediated by the H-bond and/or water molecules network(s) connecting the Cl− and Ca2+ binding sites by which proton release may be channelled

Symptomatic periesophageal vagal nerve injury by different energy sources during atrial fibrillation ablation

BackgroundSymptomatic gastric hypomotility (SGH) is a rare but major complication of atrial fibrillation (AF) ablation, but data on this are scarce.ObjectiveWe compared the clinical course of SGH occurring with different energy sources.MethodsThis multicenter study retrospectively collected the characteristics and clinical outcomes of patients with SGH after AF ablation.ResultsThe data of 93 patients (67.0 ± 11.2 years, 68 men, 52 paroxysmal AF) with SGH after AF ablation were collected from 23 cardiovascular centers. Left atrial (LA) ablation sets included pulmonary vein isolation (PVI) alone, a PVI plus a roof-line, and an LA posterior wall isolation in 42 (45.2%), 11 (11.8%), and 40 (43.0%) patients, respectively. LA ablation was performed by radiofrequency ablation, cryoballoon ablation, or both in 38 (40.8%), 38 (40.8%), and 17 (18.3%) patients, respectively. SGH diagnoses were confirmed at 2 (1–4) days post-procedure, and 28 (30.1%) patients required re-hospitalizations. Fasting was required in 81 (92.0%) patients for 4 (2.5–5) days; the total hospitalization duration was 11 [7–19.8] days. After conservative treatment, symptoms disappeared in 22.3% of patients at 1 month, 48.9% at 2 months, 57.6% at 3 months, 84.6% at 6 months, and 89.7% at 12 months, however, one patient required surgery after radiofrequency ablation. Symptoms persisted for >1-year post-procedure in 7 patients. The outcomes were similar regardless of the energy source and LA lesion set.ConclusionsThe clinical course of SGH was similar regardless of the energy source. The diagnosis was often delayed, and most recovered within 6 months, yet could persist for over 1 year in 10%