Electrochemical Fragmentation of Proteins

This thesis presents a study of three electrochemical methods applied to the fragmentation of proteins. Direct electrochemical oxidation at graphite electrodes, production of hydroxyl radicals on lead dioxide electrodes and electro-Fenton methods were each investigated as methods for fragmenting proteins. A key objective of this project was to achieve specific fragmentation, meaning that fragmentation would only occur at defined sites on each protein molecule and that this process may provide a new pathway to producing useful protein fragments. Protein fragments produced by electrochemical means were detected using mass spectroscopy and gel electrophoresis techniques. Direct electrochemical oxidation of the target proteins was studied at a graphite rod electrode in a solution containing acetonitrile, water and formic acid. β-lactoglobulin fragmentation was detected by mass spectroscopy, but fragmentation did not occur to an extent where fragments were observable by gel electrophoresis. It was evident that most of the electrolysis products appear to arise from non-cleavage oxidation reactions. The use of lead dioxide electrodes to generate hydroxyl radicals was thoroughly investigated in this work. For the first time, specific fragmentation of proteins has been achieved by direct electrochemical generation of hydroxyl radicals on the electrode surface. The pH and the chemical composition of the protein solutions were found have a strong influence on the extent of fragmentation. Electro-Fenton chemistry was conducted on a woven carbon fibre electrode. The electrode successfully reduced dissolved oxygen to produce hydrogen peroxide and regenerated Fe(II) from Fe(III). Cell conditions were optimized for applied current, method of oxygen delivery and cell division. The Fenton reaction between hydrogen peroxide and Fe(II) produced hydroxyl radicals that were able to specifically fragment proteins. It was not possible to increase the concentration of these protein fragments by increasing the hydrogen peroxide concentration, as the fragmentation products were also further fragmented. Electrochemical protein fragmentation was achieved in all three electrochemical systems, however the most promising results were achieved by electrochemical generation of hydroxyl radicals on a lead dioxide electrode. This work has the potential to become a fast and cost effective method for the fragmentation of proteins required for nutrition and medical purposes or for use in protein identification analysis with mass spectroscopy