DIRECT ELECTROCHEMISTRY OF MYOGLOBIN AND CYTOCHROME P450(CAM) IN ALTERNATE LAYER-BY-LAYER FILMS WITH DNA AND OTHER POLYIONS

Alternate layer-by-layer polyion adsorption onto gold electrodes coate d with chemisorbed mercaptopropanesulfonic acid gave stable, electroac tive multilayer films containing the proteins myoglobin and cytochrome P450(cam). Direct, reversible, electron exchange between gold electro des and proteins involved heme Fe-III/Fe-II redox couples. With oxygen in solution, electrons were also transferred to the Fe-II-O-2 complex es of these proteins, a key step for oxidative enzyme catalysis. Film assembly for Mb was done by sequential adsorption with poly(styrenesul fonate) (PSS), DNA, or poly(dimethyl diallyl) ammonium chloride (PDDA) . Cyt P450(cam) was assembled with layers of PSS or PDDA. Quartz cryst al microbalance and voltammetric studies on the same films allowed qua ntitation of electroactive and nonelectroactive protein. At pH 5.5, th e first protein monolayer in all films was fully electroactive. A seco nd monolayer added 30-40% redox activity, but additional protein layer s did not communicate with the electrode. Using various film construct ion strategies, Mb monolayers were also placed at distances from the e lectrodes of 0.5; 1.8, and 3.8 nm. Full electroactivity was found at 0 .5 nm, and about 70-80% electroactivity at 1.8 and 3.8 nm. Results sug gest the possibility of enhanced electron transport by partial intermi xing of protein and nonprotein layers. Polyion films containing Mb and cyt P450(cam) were active for enzyme-like catalysis of styrene epoxid ation in aerobic solutions.