Facilitated electron transfer from an electrode to horseradish peroxidase in a biomembrane-like surfactant film

Direct electron transfer was found to be greatly facilitated for horseradis h peroxidase (HRP) in a didodecyldimethylammonium bromide (DDAB biomembrane -like film at a pyrolytic graphite (PG) electrode involving the Fe-III \ Fe -II couple. The heterogeneous electron transfer rate constant k(s), was fit ted as 9.0 s(-1) using the non-linear regression analysis of the square wav e voltammograms at a series of frequencies and pulse heights. The pH depend ence of the formal potential for HRP in DDAB film at medium pH environments suggested one-proton transfer coupled with a one-electron transfer reactio n. Scanning electron microscopy (SEM) showed different film morphology for HRP and HRP-DDAB films. UV-vis and reflectance absorption infrared (RAIR) s pectra inferred that the heme state of HRP in DDAB film was similar to that in its native state. Circular dichroism (CD) results indicated slight pert urbation of DDAB on the second structure of HRP. Thus, the embedded HRP in the biomembrane-like DDAB film showed nearly native structural properties a nd improved electrochemical characteristics. This has potential value for t he basic and applied bioelectrochemistry of enzymes. (C) 2000 Elsevier Scie nce S.A. All rights reserved.