Plants cytochrome

Electron Transport Between Photosystem I and Photosystem II Inhibitors. The interaction between PSI and PSII reaction centers (Fig. 1) depends on the thermodynamically favored transfer of electrons from low redox potential carriers to carriers of higher redox potential. This process serves to communicate reducing equivalents between the two photosystem complexes. Photosynthetic and respiratory membranes of both eukaryotes and prokaryotes contain stmctures that serve to oxidize low potential quinols while reducing high potential metaHoproteins (40). In plant thylakoid membranes, this complex is usually referred to as the cytochrome b /f complex, or plastoquinolplastocyanin oxidoreductase, which oxidizes plastoquinol reduced in PSII and reduces plastocyanin oxidized in PSI (25,41). Some diphenyl ethers, eg, 2,4-dinitrophenyl 2 -iodo-3 -methyl-4 -nitro-6 -isopropylphenyl ether [69311-70-2] (DNP-INT), and the quinone analogues,... 

Furthermore, as shown in Figure 5.28, the number of amino acid differences between two cytochrome c sequences is proportional to the phylogenetic difference between the species from which they are derived. The cytochrome c in humans and in chimpanzees is identical human and another mammalian (sheep) cytochrome c differ at 10 residues. The human cytochrome c sequence has 14 variant residues from a reptile sequence (rattlesnake), 18 from a fish (carp), 29 from a mollusc (snail), 31 from an insect (moth), and more than 40 from yeast or higher plants (cauliflower). 

Another important group of cytochromes, found in plants, bacteria and animals is cytochrome P-450, so-called because of the absorption at 450 nm characteristic of their complexes with CO. Their function is to activate... 

Mechanistic studies have shown that TBT and certain other forms of trialkyltin have two distinct modes of toxic action in vertebrates. On the one hand they act as inhibitors of oxidative phosphorylation in mitochondria (Aldridge and Street 1964). Inhibition is associated with repression of ATP synthesis, disturbance of ion transport across the mitochondrial membrane, and swelling of the membrane. Oxidative phosphorylation is a vital process in animals and plants, and so trialkyltin compounds act as wide-ranging biocides. Another mode of action involves the inhibition of forms of cytochrome P450, which was referred to earlier in connection with metabolism. This has been demonstrated in mammals, aquatic invertebrates and fish (Morcillo et al. 2004, Oberdorster 2002). TBTO has been shown to inhibit P450 activity in cells from various tissues of mammals, including liver, kidney, and small intestine mucosa, both in vivo and in vitro (Rosenberg and Drummond 1983, Environmental Health Criteria 116). 

Riviere, J.-L. and Cabanne, F. (1987). Animal and plant cytochrome P-450 systems. Biochimie 69, 743-752. 

Scott, J.G., Liu, N.A., and Wen, Z. (1998). Insect cytochromes P450 diversity, insect resistance and tolerance to plant toxins. In D.R. Livingstone and J.J. Stegeman (Eds.) Forms and Function of Cytochrome P450, 147-156. 

The cytochromes are iron-containing hemoproteins in which the iron atom oscillates between Fe + and Fe + during oxidation and reduction. Except for cytochrome oxidase (previously described), they are classified as dehydrogenases. In the respiratory chain, they are involved as carriers of electrons from flavoproteins on the one hand to cytochrome oxidase on the other (Figure 12-4). Several identifiable cytochromes occur in the respiratory chain, ie, cytochromes b, Cp c, a, and (cytochrome oxidase). Cytochromes are also found in other locations, eg, the endoplasmic reticulum (cytochromes P450 and h, and in plant cells, bacteria, and yeasts. 

Mammalian cytochrome P450 2E1 was introduced into tobacco plants that were exposed to trichloroethene in hydroponic medium for 5 d. Trichloroethene epoxide was produced initially, and was rearranged to trichloroacetaldehyde, which was then reduced to trichloro-ethanol. This was found in samples of leaves, stems, and roots, but was absent in the control plants. Trichloroethanol was subsequently transported to the leaves where it was apparently metabolized (Doty et al. 2000). 

Figure 12.2a. Photosynthetic Z-scheme for green plants. Abbreviations not included in the text are PQ, plastiquinone Cyt bse, a form of cytochrome b absorbing at 564 nm FD, ferredoxin FP a flavoprotein. Long vertical arrows indicate steps arising from photoactivation of pigment reaction centers dashed arrows indicate uncertain pathways.0185...

Hemoproteins which engage in electron transport — the cytochromes — are much more widely dispersed among living species and occur in microorganisms, plants and animals (13). Again there are two types of iron proteins which can perform the task of electron transport, the heme and the non-heme. The latter term has become practically synonymous... 

Peroxidase activity has long been associated with extracts of plant tissue and the crystalline enzyme from horse radish root has been studied in extenso, particularly in regard to its mechanism of action (11). Plants also contain ferredoxin and various specialized cytochromes, both of which substances play an essential role in photosynthesis (95, 96). Agavain, a crystalline proteolytic enzyme from the leaves of Agave,... 

Chappie, C. (1998) Molecular-genetic analysis of plant cytochrome P450-dependent monooxygenases. Annual Review of Plant Physiology and Plant Molecular Biology, 49, 311-343. 

Leonard, E. and Koffas, M.A. (2007) Engineering of artificial plant cytochrome P450 enzymes for synthesis of isoflavones by Escherichia coli. Applied and Environmental Microbiology, 73, 7246—7251. 

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