ENZYME ELECTRODE FOR THE DETERMINATION OF L-LYSINE

Abstract

An enzyme electrode for the determination of L-lysine is described. The electrode is based on the catalytic action of a L-lysin.~-oxidase from Tbichoderma viride i4 which converts L-lysine, Oo and water into 2-0xo-6-aminocaproate, NH3 and hydrogen peroxide. Two of the reaction partners, 02 and H202, can easily be detected by electrochemical methods and offer the opportunity to install a sensitive and specific determination of L-iysine for which other reliable or low cost methods do not exist. The enzyme was isolated from the culture extracts of Trichoderma and purified according to a newly developed method described elsewhere (1). Compared with the purification scheme for a similar enzyme from Trichoderma viride Y244-2 this procedure is a different approach. It makes use of the enzyme*s unusual stability in the pH-range near its isoelectric point of pH 4.3. It provides a highly purified protein (homogeneous in 15 % SDS géls) with specific activities of 90 U/mg of protein and yields of more than 50 %. Only two steps are necessary to purify it from the bulk material of the culture extracts. To prepare it for the electrode bhe enzyme is precipitated from its aqueous solution by the addition of acetone, collected by centrifugation and fixed on tovthe membrane by a recently developed polymerization protocol. First measurements with the lysine oxidase electrode have demonstrated a linear relationship between L-lysine concentrations and the signal output. A comparison between determinations of L-lysine with the electrode and determinations done with an amino acid analyzer indicated no significant difference between the two methods.