Purification and characterization of thermostable and nonthermostable 2- haloacid dehalogenases with different stereospecificities from Pseudomonas sp. strain YL

Abstract

Two novel hydrolytic dehalogenases, thermostable L-2-haloacid dehalogenase (L-DEX) inducibly synthesized by 2-chloropropionate (2-CPA) and nonthermostable DL-2-haloacid dehalogenase (DL-DEX) induced by 2- chloroacrylate, were purified to homogeneity from Pseudomonas sp. strain YL. DL-DEX consisted of a monomer with a molecular weight of about 36,000 and catalyzed the dehalogenation of L and D isomers of 2-CPA to produce D- and L- lactates, respectively. It acted on 2-haloalkanoic acids with a carbon chain length of 2 to 4. The maximum activity on DL-2-CPA was found at pH 10.5 and 45°C. L-DEX, composed of two subunits with identical molecular weights of 27,000, catalyzes the dehalogenation of L-2-haloalkanoic acids to produce the corresponding D-2-hydroxyalkanoic acids. The enzyme acts not only on short- carbon-chain 2-haloacids such as monochloroacetate and monoiodoacetate in aqueous solution but also on long-carbon-chain 2-haloacids such as 2- bromohexadecanoate in n-heptane. L-DEX is thermostable: it retained its full activity upon heating at 60°C for 30 min. The pH and temperature optima for dehalogenation of L-2-CPA were 9.5 and 65°C, respectively. L-DEX was strongly inhibited by modification of carboxyl groups with 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide and Woodward reagent K, but DL-DEX was not.