Photosynthesis electron transport

Yanase, D., Andoh, A., and Yasudomi, N. 1990. A new simple bioassay to evaluate photosynthesis electron-transport inhibition utilizing paraquat phytotoxicity. Pestic. Biochem. Physiol. 32, 92-98... 

These potent biological reductants and oxidants provide all the energy needed to drive all subsequent reactions of photosynthesis electron transport, ATP synthesis, and CO2 fixation. 

Samuelsson G, Oquist G. Effects of copper chloride on photosynthesis electron transport and chlorophyll-protein complexes of Spinacia oleracea. Plant Cell Physiol 1980 21 445-454. 

Becerril JM, Munoz-Rueda A, Aparicio-Tejo P et al. The effects of cadmium and lead on photosynthesis electron transport in clover and lucerne. Plant Physiol Biochem 1988 26(3) 357-363. 

Table 1. The effect of infection with TMV strains PV42 and PV230 on photosynthesis, electron transport and virus accumulation in tobacco leaves.

A. Trebst and M. Avron, eds.. Photosynthesis P. Photosynthetic Electron Transport andPhotophosphorylation, Tnyclopedia of Plant Physiolog i, NS., Springer-Vedag, Berlin, 1977. 

The quantum yield of photosynthesis, the amount of product formed per equivalent of light input, has traditionally been expressed as the ratio of COg fixed or Og evolved per quantum absorbed. At each reaction center, one photon or quantum yields one electron. Interestingly, an overall stoichiometry of one translocated into the thylakoid vesicle for each photon has also been observed. Two photons per center would allow a pair of electrons to flow from HgO to NADP (Figure 22.12), resulting in the formation of 1 NADPH and Og. If one ATP were formed for every 3 H translocated during photosynthetic electron transport, 1 ATP would be synthesized. More appropriately, 4 hv per center (8 quanta total) would drive the evolution of 1 Og, the reduction of 2 NADP, and the phosphorylation of 2 ATP. 

In contrast to common usage, the distinction between photosynthetic and respiratory Rieske proteins does not seem to make sense. The mitochondrial Rieske protein is closely related to that of photosynthetic purple bacteria, which represent the endosymbiotic ancestors of mitochondria (for a review, see also (99)). Moreover, during its evolution Rieske s protein appears to have existed prior to photosynthesis (100, 101), and the photosynthetic chain was probably built around a preexisting cytochrome be complex (99). The evolution of Rieske proteins from photosynthetic electron transport chains is therefore intricately intertwined with that of respiration, and a discussion of the photosynthetic representatives necessarily has to include excursions into nonphotosynthetic systems. 

Studies (see, e.g., (101)) indicate that photosynthesis originated after the development of respiratory electron transfer pathways (99, 143). The photosynthetic reaction center, in this scenario, would have been created in order to enhance the efficiency of the already existing electron transport chains, that is, by adding a light-driven cycle around the cytochrome be complex. The Rieske protein as the key subunit in cytochrome be complexes would in this picture have contributed the first iron-sulfur center involved in photosynthetic mechanisms (since on the basis of the present data, it seems likely to us that the first photosynthetic RC resembled RCII, i.e., was devoid of iron—sulfur clusters). 

Boundary membranes play a key role in the cells of all contemporary organisms, and simple models of membrane function are therefore of considerable interest. The interface of two immiscible liquids has been widely used for this purpose. For example, the fundamental processes of photosynthesis, biocatalysis, membrane fusion and interactions of cells, ion pumping, and electron transport have all been investigated in such interfacial systems. 

Unlike the photosynthetic apparatus of photosynthetic bacteria, that of cyanobacteria consits of two photosystems, PS I and II, connected by an electron transport chain. The only chlorophyll present is chlorophyll a, and, therefore, chlorophylls b—d are not of interest in this article. Chlorophyll a is the principal constituent of PS I. Twenty per cent of isolated pigment-protein complexes contain one P700 per 20—30 chlorophyll a molecules the other 80% contain only chlorophyll a20). The physical and chemical properties of chlorophyll a and its role in photosynthesis have recently been described by Meeks77), Mauzerall75), Hoch60), Butler10), and other authors of the Encyclopedia of Plant Physiology NS Vol. 5. 

Chan. T.-M. Ulrich. E.L. Markley, J.L. Photosynthesis II, Electron Transport and Photophospharylatioif1, ed. G. Akoyunoglou, 1981, Balaban Int. Science Services, Pa. p697. 

Metal complexes of the porphyrins have been studied for many years. Such attention is not surprising, since particular derivatives play a central role in photosynthesis, dioxygen transport and storage as well as other fundamental processes such as electron transfer (Smith, 1975 Dolphin, 1978-9). Indeed, there are few compounds found in nature which can compare with the diversity of biochemical functions exhibited by the porphyrins. 

Atrazine enters plants primarily by way of the roots and secondarily by way of the foliage, passively translocated in the xylem with the transpiration stream, and accumulates in the apical meristems and leaves (Hull 1967 Forney 1980 Reed 1982 Wolf and Jackson 1982). The main phytotoxic effect is the inhibition of photosynthesis by blocking the electron transport during Hill reaction of photosystem II. This blockage leads to inhibitory effects on the synthesis of carbohydrate, a reduction in the carbon pool, and a buildup of carbon dioxide within the leaf, which subsequently causes closure of the stomates, thus inhibiting transpiration (Stevenson et al. 1982 Jachetta et al. 1986 Shabana 1987). 

The amide functionality plays an important role in the physical and chemical properties of proteins and peptides, especially in their ability to be involved in the photoinduced electron transfer process. Polyamides and proteins are known to take part in the biological electron transport mechanism for oxidation-reduction and photosynthesis processes. Therefore studies of the photochemistry of proteins or peptides are very important. Irradiation (at 254 nm) of the simplest dipeptide, glycylglycine, in aqueous solution affords carbon dioxide, ammonia and acetamide in relatively high yields and quantum yield (0.44)202 (equation 147). The reaction mechanism is thought to involve an electron transfer process. The isolation of intermediates such as IV-hydroxymethylacetamide and 7V-glycylglycyl-methyl acetamide confirmed the electron-transfer initiated free radical processes203 (equation 148). 

Most mechanisms which control biological functions, such as cell respiration and photosynthesis (already discussed in Chapter 5, Section 3.1), are based on redox processes. In particular, as shown again in Figure 1, it is evident that, based on their physiological redox potentials, in photosynthesis a chain of electron carriers (e.g. iron-sulfur proteins, cytochromes and blue copper proteins) provides a means of electron transport which is triggered by the absorption of light. 

Plastocyanin from parsley, a copper protein of the chloroplast involved in electron transport during photosynthesis, has been reported to have a fluorescence emission maximum at 315 nm on excitation at 275 nm at pH 7 6 (2°8) gjncc the protein does not contain tryptophan, but does have three tyrosines, and since the maximum wavelength shifts back to 304 nm on lowering the pH to below 2, the fluorescence was attributed to the emission of the phenolate anion in a low-polarity environment. From this, one would have to assume that all three tyrosines are ionized. A closer examination of the reported emission spectrum, however, indicates that two emission bands seem to be present. If a difference emission spectrum is estimated (spectrum at neutral pH minus that at pH 2 in Figure 5 of Ref. 207), a tyrosinate-like emission should be obtained. 

Quinones are widespread in natnre (Thomson, 1971) and have a variety of functions in the life cycles of most kinds of living organisms. These diketones are fonnd in higher plants, fungi, bacteria, and throughout the animal kingdom, and they play a central role in many biosynthetic processes that involve electron transport, such as cellular respiration (nbiqninone) and photosynthesis (plastoqninone). Vitamin K is an important factor in blood... 

Marine organisms concentrate metals in their tissues and skeletal materials. Many of these trace metals are classified as micronutrients because they are required, albeit in small amounts, for essential metabolic functions. Some are listed in Table 11.4, illustrating the role of metals in the enzyme systems involved in glycolysis, the tricarboxylic acid cycle, the electron-transport chain, photosynthesis, and protein metabolism. These micronutrients are also referred to as essential metals and, as discussed later, have the potential to be biolimiting. 

Fe Cytochrome oxidase reduction of oxygen to water Cytochrome P-450 0-insertion from O2, and detoxification Cytochromes b and c electron transport in respiration and photosynthesis Cytochrome f photosynthetic electron transport Ferredoxin electron transport in photosynthesis and nitrogen fixation Iron-sulfur proteins electron transport in respiration and photosynthesis Nitrate and nitrite reductases reduction to ammonium... 

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