Electroactive films of alternately layered polycations and iron-sulfur protein putidaredoxin on gold

Layered, electrochemically active films of bacterial iron-sulfur protein pu tidaredoxin (Pdx) and poly(dimethyldiallyammonium) (PDDA) polycations were constructed on gold electrodes coated with mercaptopropane sulfonate (MPS) and on quartz slides. Second-derivative UV-vis spectra suggested similar st ructures of Pdx in films and solutions at pH 7. Direct electrochemistry was achieved between Pdx and gold electrodes in these films, with significantl y better electrochemical reversibility than in cast Nafion-lipid-Pdx films. A formal potential dispersion model gave a good fit to square wave voltamm ograms by regression analysis and was used to estimate an average apparent rate constant of 4.5 s(-1). Reduced Pdx in the polyion films did not react with its natural redox partner cytochrome P450(cam) because of unfavorable thermodynamics in the film environment. (C) 2000 Academic Press.