Search results for "Cytochrome"
showing 10 items of 607 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…
The concentration of Cytochrome f and P700 in chlorophyll-deficient mutants of Chlorella fusca
1977
The ratio of Chlorophyll: Cytochrome f and of Chlorophyll: P700 (reaction center pigment in photosystem I) is essentially lower in chlorophyll-deficient mutants than in the normal green strain. On a dry weight basis, the mutants have the same or a higher content of redox enzymes than the normal form. The size of the photosynthetic unit of the mutants is 4 to 7 times smaller than that of the normal strains, due mainly to a deficiency of the light-harvesting chlorophyll-protein complex.
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…
Changes in the Content of Chlorophyll and Redox Components of the Thylakoid Membrane during Development and Senescence of Beech (Fagus sylvatica) Lea…
1995
Abstract Leaves from 145-year-old and 44-year-old beech trees were harvested during 1991-1993. Chlorophyll (Chl) and redox components of the thylakoid membrane, including P-700, cytochrome f (Cyt f) and D1 protein, were determined with the following results. Chl a + b, P-700 and Cyt f per unit of fresh weight (FW), dry weight (DW) and leaf area (LA) increase significantly during leaf development. This can be attributed to a massive membrane synthesis and new thylakoid formation in the cells. The Chl a/Chl b ratio decreases with the synthesis of Chl during the development of beech leaves and is reduced further with Chl breakdown in the stage of senescence. When expressed on the basis of Chl…
The Effect of Blue and Red Light on the Content of Chlorophyll, Cytochrome f, Soluble Reducing Sugars, Soluble Proteins and the Nitrate Reductase Act…
1980
The photosynthetic characteristics of many species of plants are influenced by the light intensity under which the plant is grown. This is shown by the light saturation curves for CO2 uptake. Both the light intensity required for saturation and the light-saturated rate of CO2 uptake increase with the light intensity under which the plant is grown. Photosynthetic adaptation to different light levels involves balanced changes of many leaf factors. Low-light and high-light plants differ in a number of component steps of photosynthesis as well as in the structure and composition of the photosynthetic apparatus and in the leaf anatomy (see reviews by Boardman 1977; Wild 1979).
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…
Biotransformation of caffeine and theophylline in mammalian cell lines genetically engineered for expression of single cytochrome P450 isoforms
1992
Primary steps in the metabolism of caffeine and theophylline are cleavage of methyl groups and/or hydroxylation at position 8, mediated by cytochromes P450. V79 Chinese hamster cells genetically engineered for stable expression of single forms of rat cytochromes P450IA1, P450IA2 and P450IIBI and human P450IA2 and rat liver epithelial cells expressing murine P450IA2 were used to overcome problems arising in the proper allocation of metabolic pathways to specific isoforms by conventional techniques. These cell lines were exposed to caffeine and/or theophylline, and concentrations of metabolites formed in the medium were determined by HPLC. Caffeine was metabolized by human, rat and murine P45…