Polypyrrole-Entrapped Quinohemoprotein Alcohol Dehydrogenase. Evidence for Direct Electron Transfer via Conducting-Polymer Chains

It is reported for the first time that direct electron-transfer processes between a polypyrrole (PPY) entrapped quinohemoprotein alcohol dehydrogenase from Gluconobacter sp. 33 (QH-ADH) and a platinum electrode take place via the conducting-polymer network. The cooperative action of the enzyme-integrated prosthetic groups--pyrroloquinoline-quinone and hemes--is assumed to allow this electron-transfer pathway from the enzyme's active site to the conducting-polymer backbone. A hypothetical model of the electron transfer is proposed which is supported by the influence of various parameters, such as, e.g., ionic strength and nature of the buffer salts. This unusual electron-transfer pathway leads to an accentuated increase of the K M app value (102 mM) and hence to a significantly increased linear detection range of an ethanol sensor based on this enzyme.