Purification and Characterization of the Crown Gall-specific Enzyme, Octopine Synthase

Abstract

A single enzyme catalyzes the synthesis of all 4 N2-(1-carboxyethyl)- amino acid derivatives found in a crown galltumor tissue induced by Agrobacterium tumefaciens (E.F. Sm and Town.) Conn strain B6 on sunflower (Helianthus annuus L.). This enzyme, octopine synthase, was purified by ammonium sulfate fractionation and chromatography on diethylaminoethylcellulose, blue agarose and hydroxylapatite. The purified enzyme has all the N2-(1-carboxyethyl)-amino acid synthesizing activities found in crude preparations, and the relative activities with 6 amino acids remain nearly constant during purification. Although the maximum velocities (V) and Michaelis constants (Km) differ, the ratio V/Km is the same for all amino acid substrates. Thus, an equimolar mixture of amino acids will give rise to an equimolar mixture of products. The kinetic properties of the enzyme are consistent with a partially orderded mechanism with arginine (NADPH, then arginine or pyruvate). Octopine synthase is a monomeric enzyme with a MW of 39,000 by gel filtration and 38,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.