Electron-transfer reactions copper proteins

The NO/NO+ and NO/NO- self-exchange rates are quite slow (42). Therefore, the kinetics of nitric oxide electron transfer reactions are strongly affected by transition metal complexes, particularly by those that are labile and redox active which can serve to promote these reactions. Although iron is the most important metal target for nitric oxide in mammalian biology, other metal centers might also react with NO. For example, both cobalt (in the form of cobalamin) (43,44) and copper (in the form of different types of copper proteins) (45) have been identified as potential NO targets. In addition, a substantial fraction of the bacterial nitrite reductases (which catalyze reduction of NO2 to NO) are copper enzymes (46). The interactions of NO with such metal centers continue to be rich for further exploration. 

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. 

Blue copper proteins are a family of metalloproteins that have been found to play an important role in a number of electron-transfer reactions in nature. Solomon and coworkers have studied a range of blue copper enzymes in detail to produce a thorough description of how molecular and electronic structure interact to provide the function of these enzymes (26,158). 

Structure and Electron Transfer Reactions of Blue Copper Proteins... 

In this complex, there are two optically active sites. Spinach plastocyanin is a type I copper protein, in which two reactive sites have been identified on its surface, at least. The electron transfer reaction occurs with significantly large stereoselectivity the ratio of the observed reaction rate constant (k /k ) is 1.6 to 2.0. The difference in the activation enthalpy, AAH a, is 3.0 kJ mol-1, and the difference in the activation entropy, AS (a-a) is 15 J mol-1 K-1. This means that the stereoselectivity arises from the entropy term. 

The electron transfer reaction from copper to heme within the ternary protein complex was also studied in solution by stopped-flow spectroscopy. Analysis by Marcus theory of the temperature dependence of the limiting first-order rate constant for the redox reaction (Davidson and Jones, 1996) yielded values for the of 1.1 eV and H b of 0.3 cm , and predicted an electron transfer distance between redox centers which was consistent with the distance seen in the crystal structure. Thus, the electron transfer event is rate-limiting for this redox reaction. Experiments are in progress to determine the validity of the predicted pathways for electron transfer shown in Figure 7. 

Copper Hemocyanrn/Tyrosinase Models Copper Proteins with Dinuclear Active Sites Copper Proteins with Type 1 Sites Copper Proteins with Type 2 Sites Cytochrome Oxidase Electron Transfer Reactions Theory Long-range Electron Transfer in Biology Metal Ion Toxicity Metal-related Diseases of Genetic Origin Metallochaperones Metal Ion Homeostasis Nutritional Aspects of Metals Trace Elements. 

The type 1 copper proteins participate in electron-transfer reactions with a wide variety of partners, including inorganic... 

The nse of polysnlfide complexes in catalysis has been discnssed. Two major classes of reactions are apparent (1) hydrogen activation and (2) electron transfers. For example, [CpMo(S)(SH)]2 catalyzes the conversion of nitrobenzene to aniline at room temperature, while (CpMo(S))2S2CH2 catalyzes a number of reactions snch as the conversion of bromoethylbenzene to ethylbenzene and the rednction of acetyl chloride, as well as the rednction of alkynes to the corresponding cw-alkenes. Electron transfer reactions see Electron Transfer in Coordination Compounds) have been studied because of their relevance to biological processes (in, for example, ferrodoxins), and these cluster compounds are dealt with in Iron-Sulfur Proteins. Other studies include the use of metal polysulfide complexes as catalysts for the photolytic reduction of water by THF and copper compounds for the hydration of acetylene to acetaldehyde. ... 

Copper Proteins with Type 1 Sites Cytochrome Oxidase Electron Transfer in Coordination Compounds Electron Transfer Reactions Theory Iron Heme Proteins Electron Transport Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases Photosynthesis. 

Quenching of excited-state [Ru(bipy)3] by reduced blue proteins involves electron transfer from the Cu with rate constants close to the diffusion limit for electron-transfer reactions in aqueous solution. It is suggested that the excited Ru complex binds close to the copper-histidine centre, and that outer-sphere electron transfer occurs from Cu through the imidazole groups to Ru. Estimated electron-transfer distances are about 3.3 A for plastocyanin and 3.8 A for azurin, suggesting that the hydrophobic bipy ligands of Ru " penetrate the residues that isolate the Cu-His unit from the solvent. ... 

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