Intramolecular electron transfer ceruloplasmin

Machonkin, T. E. and Solomon, E. T. (2000) The thermodynamics, kinetics, end molecular mechanism of intramolecular electron transfer in human ceruloplasmin, J. Am. Chem. Soc. 122,12547-12560. 

Studies of intramolecular ET in oxidases provide interesting examples of how pulse radiolysis is employed to obtain insights into both (1) these enzymes respective mechanisms of action and (2) electron transfer along protein polypeptide matrices that were most probably selected by evolution (9,10, 30-32). Thus, early attempts to study the electron uptake mechanism by the blue oxidase, ceruloplasmin, showed that a diffusion-controlled decay process of the eaq in solutions of this protein is paralleled by the formation of transient optical absorptions due to electron adducts of protein residues, primarily of cystine disulfide bonds (30). The monomolecular decay of the latter absorption was found to have the same rate constant as that at which the type 1 Cu(II) absorption band was reduced. These results were interpreted as being the combined result of the high reactivity of the e q and the relatively inaccessible type 1 Cu(II) site, yielding an indirect, intramolecular electron transfer pathway from surface-exposed residues (30). 

The inhibition of ceruloplasmin is also quite comphcated, and a part of this may be associated with the suggested conformational sensitivity of the molecule. Azide, at least, inhibits by decreasing the rate of decomposition of the 420 nm absorbing intermediate, possibly by inhibiting intramolecular electron transfer reactions necessary for the reduction of O2 to H2O. 

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