Electron-Transferring Copper Proteins

Figure 2-16 Beta cylinders. (A) Stereoscopic a-carbon plot of plastocyanin, a copper-containing electron-transferring protein of chloroplasts. The copper atom at the top is also shown coordinated by the nitrogen atoms of two histidine side chains. The side chains of the aromatic residues phenylalanines 19,29, 35,41, 70, and 82 and tyrosines 80 and 83 are also shown. Most of these form an internal cluster.

Most proteins in the PS-11 complex are membrane spanning, but the three extrinsic proteins that are involved in oxygen evolution are located on the lumenal side of the thylakoid membrane. Although most proteins in the PS-1 complex are also membrane-spanning, a few are located toward the stromal side of the thylakoid membrane, e.g., the iron-sulfur proteins that contain FeS-A and FeS-B and the Fd-docking protein. On the other hand, some mobile electron-transfer proteins are present on one side or the other of the membrane, with Fd present on the stromal side and near the ferredoxin-NADP" -reductase (FNR) and the FNR-binding protein, and the copper-protein electron carrier, plastocyanin (PCy), present on the lumenal side, close to the PS-1 primary donor P700. 

Marcus theory has been used to interpret the reactions of cytochromes c and blue copper proteins. For thirteen protein-protein electron-transfer reactions, the data can be fitted with the self-exchange rate constants of 2.8 x 10 s ... 

Copper Blue Proteins.— The present understanding of the chemistry of the copper blue electron-transfer proteins has taken a significant step forward with the publication of molecular structures for azurin and plastocyanin. ... 

Structure and electron transfer reactivity of the blue copper protein, plastocyanin. A. G. Sykes, Chem. Soc. Rev., 1985,14, 283 (117). 

Blue copper electron transfer proteins, 6,712-717 Blue copper oxidases, 6,699 Blue copper proteins, 2, 557 6, 649 Blue electron transfer proteins, 6,649,652 spectroscopy, 6, 651 Blue oxidases copper, 6,654,655 Blueprint process, 6,124 Blue proteins model studies, 6,653 Boleite... 

The many redox reactions that take place within a cell make use of metalloproteins with a wide range of electron transfer potentials. To name just a few of their functions, these proteins play key roles in respiration, photosynthesis, and nitrogen fixation. Some of them simply shuttle electrons to or from enzymes that require electron transfer as part of their catalytic activity. In many other cases, a complex enzyme may incorporate its own electron transfer centers. There are three general categories of transition metal redox centers cytochromes, blue copper proteins, and iron-sulfur proteins. 

C20-0102. Blue copper proteins are blue when they contain Cu but colorless as Cu compounds. The color comes from an interaction in which a photon causes an electron to transfer from a sulfur lone pair on a cysteine iigand to the copper center. Why does this charge transfer interaction occur for Cu but not Cu+ ... 

The enzymes are protein molecules having globular structure, as a rule. The molecular masses of the different enzymes have values between ten thousands and hundred thousands. The enzyme s active site, which, as a rule, consists of a nonproteinic organic compound containing metal ions of variable valency (iron, copper, molybdenum, etc.) is linked to the protein globule by covalent or hydrogen bonds. The catalytic action of the enzymes is due to electron transfer from these ions to the substrate. The protein part of the enzyme secures a suitable disposition of the substrate relative to the active site and is responsible for the high selectivity of catalytic action. 

It is interesting to speculate why nitrite reductase has its type I coppers in domains 1, whereas in hCP the mononuclear copper binding sites are retained in the domains 2,4, and 6 where they are comparatively buried in the protein. One possible reason can be related to the difference in functions of the two proteins. NR has to interact with a relatively large pseudo-azurin macromolecule in order for electron transfer to take place,... 

Copper, Cu+(d10), Cu2+ (d9) 4, tetrahedral N-Thiolate, thioether, AMmidazole Electron transfer in Type I blue copper proteins... 

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