Purification and characterization of an acetyl xylan esterase produced by Streptomyces lividans

Abstract

The acetyl xylan esterase cloned homologously from Streptomyces lividans was purified from culture filtrate of the overproducing strain S. lividans IAF43. The secreted enzyme had a molecular mass of 34 kDa and a pI of 9.0. Under the assay conditions with chemically acetylated birchwood xylan the kinetic constants of the enzyme were: specific activity, 715 units/mg, K(m) 7.94 mg/ml and V(max) 1977 units/mg. Optimal enzyme activity was obtained at 70°C and pH 7.5. Hydrolysis assays with different acetylated substrates showed that the enzyme is specific for deacetylating the O-acetyl group of polysaccharides and is devoid of N-deacetylation activity. Sequential hydrolysis shows that its action is essential for the complete degradation of acetylated xylan by the xylanases of S. lividans.