Low-specificity L-threonine aldolase of Pseudomonas sp. NCIMB 10558:: purification, characterization and its application to β-hydroxy-α-amino acid synthesis

Low-specificity L-threonine aldolase, catalyzing the reversible cleavage/condensation reaction between L-threonine/L-allo-threonine and glycine plus acetaldehyde, was purified to homogeneity from Pseudomonas sp. NCIMB 10558. The enzyme has an apparent molecular mass of approximately 145 kDa and consists of four identical subunits with a molecular mass of 35 kDa. The enzyme, requiring pyridoxal-5'-phosphate as a coenzyme, is strictly L-specific at the alpha position, whereas it can not distinguish between threo and erythro forms at the beta position. Besides the reversible cleavage/condensation of threonine, the enzyme also catalyzes the reversible interconversion between glycine plus various aldehydes and L-beta-hydroxy-alpha-amino acids, including L-beta-(3,4-dihydroxyphenyl)serine, L-beta-(3,4-methylenedioxyphenyl)serine and L-beta-phenylserine, providing a new route for the industrial production of these important amino acids.