OBSERVATION OF ELECTRON-TRANSFER BETWEEN A SILVER ELECTRODE AND PUTIDAREDOXIN USING ELECTROMODULATED REFLECTANCE SPECTROSCOPY

This paper reports measurements of the redox reaction rate for the {2F e-2S} protein puditaredoxin (Pdx) on bare and bekanamycin-modified sil ver electrodes. The electron turnover rates were determined using elec troreflectance (ER) and cyclic voltammetry (CV). The measurements were analyzed with two kinetic models: (1) strongly adsorbed protein layer and (2) freely diffusing protein. For the adsorbed layer model, the r ates obtained with ER were almost two orders of magnitude greater than the rates obtained with CV. For the freely diffusing model, the rates determined by the two methods were similar, suggesting that this kine tic model is more appropriate. Modification of the Ag electrode with b ekanamycin resulted in a negative 0.1-V shift of the Pdx formal potent ial, but showed only a small increase in the observed redox reaction r ates. The measured rate constants were compared with the predictions o f the Marcus theory of electron transfer. (C) 1997 Academic Press.