Direct electron transfer between cellobiose dehydrogenase and solidmetal or graphite electrodes

Sammanfattning: Direct electron transfer (ET) between the enzyme cellobiose dehydrogenase (CDH) and different metal and graphite electrodes has been investigated. The heme domain of the CDH has been shown to play a key-role in the direct ET. A mechanism for the ET between CDH and graphite electrodes was proposed. Based on this mechanism, a kinetic model was developed. The catalytic current was studied under different experimental conditions. Thus the pH, substrate concentration and electrode potential were varied. A satisfactory correlation between the experimental data and the kinetic model was obtained.The catalytic current for the CDH-modified electrodes was dependent on the ionic strength. An increase in the NaCl concentration increased the catalytic current. This effect was assigned to the screening of negative charges close to the heme iron in CDH.A new cell for spectroelectrochemistry was developed and investigated. The cell volume was only 1 µl allowing small samples to be studied. The pH dependence of the formal potential E0’, of the heme was investigated for dissolved CDH and compared to E0’ determined by cyclic voltammetry for CDH on thiol modified gold. The result showed that there was a difference in formal potential on the order of 50 mV between dissolved and surface adsorbed CDH. However, the slope of the pH dependence was the same in both cases.A biosensor, based on a dual-electrode cell was developed. The two electrodes were based on CDH and the enzyme oligosaccharide dehydrogenase (ODH) ‘wired’ with an osmium-based redox polymer on solid graphite. The electrode system was used as an end column detector for the detection of various sugars after their separation in a size exclusion chromatographic (SEC) system.