Cytochrome self-exchange rate constants

Early reports on interactions between redox enzymes and ruthenium or osmium compounds prior to the biosensor burst are hidden in a bulk of chemical and biochemical literature. This does not apply to the ruthenium biochemistry of cytochromes where complexes [Ru(NH3)5L] " , [Ru(bpy)2L2], and structurally related ruthenium compounds, which have been widely used in studies of intramolecular (long-range) electron transfer in proteins (124,156-158) and biomimetic models for the photosynthetic reaction centers (159). Applications of these compounds in biosensors are rather limited. The complex [Ru(NHg)6] has the correct redox potential but its reactivity toward oxidoreductases is low reflecting a low self-exchange rate constant (see Tables I and VII). The redox potentials of complexes [Ru(bpy)3] " and [Ru(phen)3] are way too much anodic (1.25 V vs. NHE) ruling out applications in MET. The complex [Ru(bpy)3] is such a powerful oxidant that it oxidizes HRP into Compounds II and I (160). The electron-transfer from the resting state of HRP at pH <10 when the hemin iron(III) is five-coordinate generates a 7i-cation radical intermediate with the rate constant 2.5 x 10 s" (pH 10.3)... 

Non-adiabatic multiphonon electron tunnelling theory has been used to interpret kinetic data on a number of redox reactions of cytochrome c and yields a self-exchange rate constant for the protein of 1.7 x 10 s (ATT =4.9 kcal... 

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 ... 

Cross reactions of plastocyanins and azurins from various sources with cytochromes can be fitted to the Marcus equation using constant self-exchange rate constants of 6.6 x 10 s for the plastocyanins, 9.9 x 10 s for Ps. 

The electron self-exchange rate constant and activation parameters have been determined for trypsin-solubilized bovine liver microsomal cytochrome bs, and the reorganizational energies have been evaluated. The rate constant increases with ionic strength from 2.6x 10 s at 0.1 Af to... 

The value of the rate constant obtained for the heme undecapeptide, MPll (1.3 x 10 s ), is comparable to those of other model compounds.The rate constants for model hemes and the heme c undecapeptide are approximately a factor of 10 larger than those found in cytochromes with 80-90 amino acids. This argues further that the heme exposure to the solvent seems not to be a major factor controlling the rate constants for electron self-exchange in cytochromes. 

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