Search results for "electron transport chain"
showing 10 items of 82 documents
The Variability of the Photosynthetic Unit in Chlorella Fusca
1984
The concept of the photosynthetic unit (PSIT) was introduced by Gaffron and Wohl (1936) on the basis of Emerson and Arnold’s flash light experiments (1932). The PSU was defined as the minimum of chlorophyll molecules required for the evolution of one O2. Later on, the PSU was considered to be the complex of one reaction center and its appropriate antenna of light harvesting chlorophyll molecules. Assuming that there is an equal number of the PS I and PS II reaction centers the PSU was mostly expressed as Chl/P-700. However, recently it could be shown that the ratio of PS II/PS I is variable depending on the light conditions during growth (Kawamura et al., 1979; Myers, Graham, 1982). Further…
Measurements of cytochrome f and P-700 in intact leaves of Sinapis alba grown under high-light and low-light conditions
1978
The oxidation and reduction of cytochrome f and P-700 is measured spectrophotometrically in leaves of low-light and high-light plants. After illumination with red light, an induction phenomenon for cytochrome f oxidation is observed which indicates a regulation of photosystem I activity through energy distribution between the pigment systems by the energy state of the membrane. After far-red excitation the reduction of cytochrome f in the dark is much slower in low-light leaves. This shows that cyclic electron transport is not improved in low-light plants under these conditions. P-700 is oxidized on excitation with far-red light. However, with high intensities of far-red light, P-700 is par…
Comparative Investigations on the Photosynthetic Electron Transport Chain of Spruce (Picea Abies) with Different Degrees of Damage in the Open Air
1988
Several components of the photosynthetic electron transport chain (P-700, cytochrome f, QB-protein) as well as the rate of electron transport and the chlorophyll content of the needles of spruce trees with different degrees of damage were investigated. The investigations were carried out in pair comparison at a location in the Hunsruck (West Germany). The rate of electron transport was determined as photoreduction of 2,6-dichlorophenolindophenol. Significant damage to the electron transport system is shown in the thylakoids of the damaged trees compared to the less severely damaged trees. In the spruce trees with more damage, the rates of electron transport are significantly lower. The inve…
Studies on the Content of P 700 and Cytochromes in Sinapis alba During Growth Under Two Different Light Intensities
1975
Sinapis alba was grown under two extremely different light intensities. We obtained two different modifications which hold several physiological and biochemical characteristics comparable to the relations in light- and shade plants. In the strong light the maximum rate of CO2-uptake increases within five days to a three-fold rate. At the same time the content of several redox systems of photosynthetic electron transport increases while the content of P 700 remains equivalent in both types of plants. In the high-light plants we find a ratio P 700: Cytochrome f of 1 but a ratio of 3 in the low-light plants. These ratios could be probably essential features of various sun- and rainforest speci…
Study of electrostatic potential surface distribution of wild-type plastocyaninSynechocystissolution structure determined by homonuclear NMR
2003
Plastocyanin is a small (∼10 kDa), type I blue copper protein that works as an electron donor to photosystem I from cytochrome f in both chloroplast systems and in some strains of cyanobacteria. Comparative studies of the kinetic mechanisms of plastocyanins in different organisms show that the electron transfer from photosystem I happens by simple collision in cyanobacteria but through a intermediate transition complex in green algae and superior plants. Previous work has proved that this effect cannot be explained by structural variations across the different plastocyanins but it can be explained by differences in the electrostatic potential distribution at the protein surface. In that cas…
Measurements of manganese in thylakoids of Sinapis alba grown under high-light and low-light conditions.
1981
The manganese content of thylakoids and tissues was measured in leaves grown under high- and low-light conditions. Especially when grown in a nutrient medium enriched in manganese (20 μM), the thylakoids contained large amounts of manganese, which could be removed by EDTA washing without impairment of the Hill reaction. The unremovable content of manganese was almost the same in thylakoids from plants grown in nutrient media of normal (2 μM) and reduced (0.2 μM) manganese content. Up to this limit of manganese content, Hill activity did not seem to be impaired. 1.2 atoms Mn per 100 molecules chlorophyll were found in low-light thylakoids and 1.6 atoms Mn in high-light thylakoids. This is si…
All-Atom simulations disclose how cytochrome reductase reshapes the substrate access/egress routes of its partner cyp450s
2020
Cytochromes P450 enzymes (CYP450s) promote the oxidative metabolism of a variety of substrates via the electrons supplied by the cytochrome P450 reductase (CPR) and upon formation of a CPR/CYP450 adduct. In spite of the pivotal regulatory importance of this process, the impact of CPR binding on the functional properties of its partner CYP450 remains elusive. By performing multiple microsecond-long all-Atom molecular dynamics simulations of a 520â »000-Atom model of a CPR/CYP450 adduct embedded in a membrane mimic, we disclose the molecular terms for their interactions, considering the aromatase (HA) enzyme as a proxy of the CYP450 family. Our study strikingly unveils that CPR binding alters…
Cyclic and noncyclic photophosphorylation during the ontogenesis of high-light and low-light leaves of Sinapis alba.
1981
Noncyclic electron transport to ferricyanide and photophosphorylation as well as the methylviologen mediated aerobic and anaerobic photophosphorylation with dichlorophenolindophenol-ascorbate as the electron donor of photosystem I were measured during the development of high-light and low-light adapted leaves of Sinapis alba. Anaerobic methylviologen-catalyzed phosphorylation is more than twice as high as aerobic phosphorylation. The difference between the rates of aerobic and anaerobic phosphorylation is sensitive to dibromothymoquinone. Thus, under anaerobic conditions, methylviologen mediates a cyclic phosphorylation including plastoquinone. All photochemical activities of high-light chl…
Experimental conditions affect the site of tetrazolium violet reduction in the electron transport chain of Lactococcus lactis
2009
The reduction of tetrazolium salts to coloured formazans is often used as an indicator of cell metabolism during microbiology studies, although the reduction mechanisms have never clearly been established in bacteria. The objective of the present study was to identify the reduction mechanisms of tetrazolium violet (TV) in Lactococcus lactis using a mutagenesis approach, under two experimental conditions generally applied in microbiology: a plate test with growing cells, and a liquid test with non-growing (resting) cells. The results showed that in both tests, TV reduction resulted from electron transfer from an intracellular donor (mainly NADH) to TV via the electron transport chain (ETC), …
Synthesis and characterization of zinc carboxy–porphyrin complexes for dye sensitized solar cells
2018
Two zinc porphyrins, 2 and 8, have been synthesized. Porphyrin 8 displays better electronic communication between the dye and the TiO2 electrode. Photophysical measurements and electrochemistry experiments suggest that both porphyrins are very promising sensitizers for dye-sensitized solar cells (DSSCs). It was found that their molecular orbital energy levels favor electron injection and dye regeneration in DSSCs. Solar cells sensitized by 2 and 8 were fabricated, and it was found that they show power conversion efficiencies (PCEs) of 5.27% and 7.13%, respectively. Photovoltaic measurements (J–V curves) together with the incident photon-to-electron conversion efficiency spectra of the two c…