Azurin self-exchange rate constants

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... 

Unfortunately, experimental kn values are not available for any one of the three blue proteins. It has been established, however, that the self-exchange rates for azurin (24) and plastocyanin (25) are both slow on the NMR time scale at 25°. It is not likely that the predicted kn values from the Fe(EDTA)2 reactions will correspond to the measured self-exchange rate constants. Indeed, agreement between calculated and measured kn values is only to be expected if the activation requirements of both partners in a cross reaction are exactly the same as those used in their respective self-exchanges. Access to a buried, or at best partially exposed, outer-sphere redox center should vary substantially for different reactants, and it is likely that calculated kn values will span a wide range in such cases. 

Self-exchange rate constants have been determined for P. aeruginosa and A. dinitrificans azurin (63) and T. versutus amicyanin (68) by NMR line broadening, and for Rhus vernicifera stellacyanin by EPR... 

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. 

Stellacyanin from R. vernicifera has been modified by coordination of [Ru(NH3)5] " to surface histidines at positions 32 and 100. The rate constant and activation parameters for the intramolecular electron transfer from Ru(II) to the stellacyanin Cu(II) have been determined, and were found to be in good agreement with Marcus theory. The replacement of methionine by lysine at position 44 in P. aeruginosa azurin by site-directed mutagenesis results in a decrease in the Cu(I)/Cu(II) electron self-exchange rate constant (36 °C) from 1.3xl0 M... 

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