Plastocyanin functional role

Whatever the explanation, the sensitivity of the remote pK to oxidation state of the Cu is of potential importance in relation to the functional role of plastocyanin. Plastocyanin and its physiological electron transport partner cytochrome f are believed to have complementary surfaces which lead to efficient interaction prior to electron transfer. As will be seen below there is substantial evidence for cytochrome f(II) (as reductant) reacting at the remote site of PCu(II). One problem which may be anticipated here is how dissociation of the product... 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

Since only the cupric form is paramagnetic, ESR is an ideal method, determining and quantitating the valence state of copper in these proteins. Many are found to be a mixture of Cu and Cu, and only a few such as plastocyanin contain exclusively Cu. Studies of valence state changes of the copper in cytochrome c oxidase by ESR have demonstrated convincingly for the first time that copper plays a functional role. 

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. 

Soluble forms of cytochrome of c type are present in bacteria and, under some conditions of growth, in cyanobacteria these are considered to act as diffusable redox carriers between the oxidoreductase complexes and bacterial RC or PSI-RC, respectively. A similar role is assumed by plastocyanin in chloroplasts and in cyanobacteria (again dependeing on the conditions of growth plastocyanin biosynthesis can be repressed and replaced in its function by cyt. c). These electron carriers represent, therefore, the natural electron acceptors of the oxidoreductases and the secondary electron donors to the RC (Dj in bacteria and Dj2 in chloroplasts). 

Describe the composition and function of the cytochrome bf complex, and outline the roles of plastocyanin, Cu T and Fe-S clusters in the formation of a transmembrane proton gradient. 

The structure of the Photosystem 1 RC is nearly symmetrical, with an approximate symmetry axis running from the center of P-700 to the center of F. The electron acceptors A and A have symmetrically located counterparts, also chlorophyll a and phyUoquinone, which were first postulated to be inactive but might well play a role in electron transfer.Two additional chlorophyll a molecules are located between P-700 and Aq (and its symmetric counterpart). These molecules have not been identified as discrete intermediates in electron transfer, but they might be involved in facilitating electron transfer from P-700 to A . It should also be mentioned that the roles of most of the protein subunits are stUl not understood several serve for the docking of ferredoxin or of plastocyanin, but many small hydrophobic polypeptides have no obvious functions. 

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