Plastocyanin plant

III 595 nm, axial EPR, 1 Cys, H---C-H-M Plastocyanin" Plants, algae Cytochrome / P700... 

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,... 

From 13 completed amino-acid sequences and 54 partial sequences (>40 residues) of plastocyanins from higher plants it appears that sixty residues are invariant and 7 are conservatively substituted 02,7). With three algal plastocyanins included there are 39 invariant or conservatively substituted groups. It is believed that the same structural features apply to the whole family, and that highly conserved residues are an indication of functional sites on the protein surface. The upper hydrophobic and right-hand-side surfaces are believed to be particularly relevant in this context, the latter including four consecutive... 

Figure 1. Structure of plastocyanin (2) showing the positions of a-carbon atoms of amino acid residues. The active site and positions of the conserved (plant) negative patch (42-45) and Tyr 83 are indicated (%).

Fig. 3. Plastocyanin amino-acid sequences relevant to this review. Other sequence information is included. There are now 24 known sequences (18 formerly in Ref. [ I]). The 23 residues invariant throughout all 24 known higher plant and algal plastocyanin sequences are indicated ( ), 5 others (A) are invariant if A. variabilis is excluded, and a further 19 (o) if only the higher plant sequences are considered. Eieletions are indicated ( ), and residues which coordinate the Cu(V)...

The solution conformation of plastocyanin from French bean, spinach, and S. obliquus has now been determined from distance and dihedral angle constraints derived by NMR spectroscopy [37,40]. These two-dimensional NMR studies have indicated a well defined backbone conformation, which is very similar to that of poplar PCu in the crystalline state. However, in the case of S. obliquus there are deletions at positions S7 and 58 which influence the shape in the acidic region and in particular close to residues 59-61. The gap which is created is in effect repaired with consequent tightening of the loop 57-62 as indicated in Fig. 5. One of the pronounced bulges at the remote site of poplar and presumably other higher plant plastocyanins is not therefore present in S. obliquus (or plastocyanin from other green algae) [31, 32], as well as parsley... 

Reduction potentials (Eg) for different plastocyanins, the PCu(II)/PCu(I) couple, have been determined by spectrophotometric titration against, e.g. [Fe(CN)e] . At pH 7.5 for higher plant and green algal plastocyanins values are close to 370 mV at 25 °C, 1=0.10 M(NaCl) [1]. Thus French bean gives a value 360 mV and S. obliquus 363 mV [50]. However, A. variabilis gives an... 

There are no uncoordinated histidine residues in higher plant plastocyanins. However, some algal plastocyanins, including S. obliquus and A. variabilis have a histidine at position 59, which is of particular interest since this lies within the remote acidic patch region [132]. Differences between the two are that whereas S. obliquus PCu(I) is acidic (charge —9), A. variabilis is basic (charge 1-I-). Also S. obliquus has deletions at 57 and 58 with a consequent tightening of the peptide chain in this locality. Fig. 5. Both these plastocyanins were therefore Ru-modified. 

A macromolecular complex that allows plants to harvest the sun s photic energy by absorbing photons and using their energy to catalyze photooxidation of plastocyanin, the copper protein situated in the lumen of thylakoid membranes, which undergoes subsequent electron transfer reactions. These reactions are illustrated in Fig. 1. 

In contrast to azurin, the plant plastocyanins have a conserved negative patch of residues adjacent to a putative redox partner-binding site. Plastocyanin has, in addition, the hydrophobic face into which the edge of the second histidine ligand is inserted. 

In plants, algae and cyanobacteria the light-induced charge separation of photosynthesis occurs in 2 large membrane proteins, called photosystem (PS) I and II. PS I catalyzes the ET from plastocyanin (or cytochrome c6) on the luminal side to ferrodoxin (or flavodoxin) on the stromal side of the membrane (for review see reference 177). PS I from the cyanobacterium Thermo(Y13)synechococcus (T.) elongatus was crystallized and an X-ray crystallographic structure at 2.5 A resolution has recently been obtained.18,178 Very recently, the structure from plant PS I has also been reported with a resolution of 4.4 A.179... 

These two reaction centers in plants act in tandem to catalyze the light-driven movement of electrons from HaO to NADP+ (Fig. 19-49). Electrons are carried between the two photosystems by the soluble protein plastocyanin, a one-electron carrier functionally similar to cytochrome c of mitochondria. To replace the electrons that move from PSII through PSI to NADP+, cyanobacteria and plants oxidize H20 (as green sulfur... 

Cyanobacteria can synthesize ATP by oxidative phosphorylation or by photophosphorylation, although they have neither mitochondria nor chloroplasts. The enzymatic machinery for both processes is in a highly convoluted plasma membrane (see Fig. 1-6). Two protein components function in both processes (Fig. 19-55). The proton-pumping cytochrome b6f complex carries electrons from plastoquinone to cytochrome c6 in photosynthesis, and also carries electrons from ubiquinone to cytochrome c6 in oxidative phosphorylation—the role played by cytochrome bct in mitochondria. Cytochrome c6, homologous to mitochondrial cytochrome c, carries electrons from Complex III to Complex IV in cyanobacteria it can also carry electrons from the cytochrome b f complex to PSI—a role performed in plants by plastocyanin. We therefore see the functional homology between the cyanobacterial cytochrome b f complex and the mitochondrial cytochrome bc1 complex, and between cyanobacterial cytochrome c6 and plant plastocyanin. 

Using an alternative path of light-induced electron flow, plants can vary the ratio of NADPH to ATP formed in the light this path is called cyclic electron flow to differentiate it from the normally unidirectional or noncyclic electron flow from H20 to NADP+, as discussed thus far. Cyclic electron flow (Fig. 19-49) involves only PSI. Electrons passing from P700 to ferredoxin do not continue to NADP+, but move back through the cytochrome bef complex to plastocyanin. The path of... 

The simpler cytochrome bc] complexes of bacteria such as E. coli,102 Paracoccus dentrificans,116 and the photosynthetic Rhodobacter capsulatus117 all appear to function in a manner similar to that of the large mitochondrial complex. The bc] complex of Bacillus subtilis oxidizes reduced menaquinone (Fig. 15-24) rather than ubiquinol.118 In chloroplasts of green plants photochemically reduced plastoquinone is oxidized by a similar complex of cytochrome b, c-type cytochrome /, and a Rieske Fe-S protein.119 120a This cytochrome b6f complex delivers electrons to the copper protein plastocyanin (Fig. 23-18). 

Pinacolone, o-(diphenylphosphino)benzoyl-coordination chemistry, 401 Piperidine, IV-hydroxy-metal complexes, 797 pA a values azole ligands, 77 Plant roots amino acids, 962 carboxylic acids, 962 Plastocyanin copper binding site, 557 copper(II) complexes, 772 copper(II) site in, 770 Platinum, dichlorobis(benzonitrile)-IR spectrum, 264 Platinum, cis-dichlorodianunine-antitumor activity, 34, 979 Platinum, ethylenebis(triphenylphosphine)-reactions with 5,6-dimethyl-2,l,3-benzothiadiazole, 194 Platinum blue formation, 265 Platinum complexes acetylacetone reactions, 380 amides, 491 amidines... 

The plastocyanins are found in plant chloroplasts and other photosynthetic organisms, and act as membrane-bound electron carriers between photosystems II and I in the photosynthetic pathway of higher plants, green algae and some blue-green algae. 

Amino acid sequence data for many plastocyanins are now available. A large number of residues are conserved,910 particularly among the plastocyanins from higher plants, where about 50% of the residues are the same. Residues 31-44 and 84-93 are highly conserved in all the proteins, and provide the donor groups for copper. 

Fig. 26. Z-Scheme of photosynthesis in plants. Chi is chlorophyll, cyt b, f is cytochrome b, / PC is plastocyanine, (Fe-S) is iron sulfer protein. ATP is adenosine triphosphate ADP is adenosine diphosphate Pj is the phosphate ion and NADP is the nicotinamide adenine dinucleotide phosphate ion [203]...

The plastocyanins are blue copper proteins found in the chloroplasts of higher plants and algae where they mediate electron transport between cytochrome f and P-700 (Barber, 1983 Haehnel, 1984, 1986 Cramer etal., 1985 Sykes, 1985 Andersen et al., 1987). Plastocyanins each contain one copper bound by a single polypeptide chain of molecular weight around 10500 (Sykes, 1985). The spectroscopic properties of the copper are those of a typical blue site. The properties of the plastocyanins have been the subject of detailed reviews (Sykes, 1985 Haehnel, 1986 Chapman, 1991). 

Basic blue proteins have been isolated from a number of plant sources and have previously been referred to as plantacyanin (Aikazyan and Nalbandyan, 1975,1979 Sakurai et al, 1982). The protein from cucumber has been the most extensively studied of the basic blue proteins and the crystal structure is now available (Guss et al., 1988). The function of this basic blue protein is unknown, however, it is probably not involved in photosynthetic electron transport as it will not replace plastocyanin in that electron transport chain (Adman, 1985). 

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