Functional change of Bacillus acidocaldarius α-amylase chemically modified with periodate oxidized polysaccharides

Abstract

Abstract α-amylase from isolated bacterial strain (Bacillus acidocaldarius) was chemically modified by covalent coupling to several periodate oxidized polysaccharides. Conjugated enzyme with oxidized dextran (MW 84 kDa) retained the highest activity (77.4%) and the highest specific activity (3948.4 U/mg protein). Compared to the native enzyme, the dextran conjugated α-amylase exhibited higher optimum temperature, higher Km (Michaelis constant), lower Vmax (maximal reaction rate), lower Vmax/Km (catalytic efficiency), lower Ea (activation energy), lower deactivation constant rate (kd), higher half-life time (t1/2), and higher decimal reduction time values (D). Covalent attachment of α- amylase to oxidized dextran brought about significant enhancement of thermal stability, stability at extreme pHs, and resistance against the inhibitors. In the presence of the substrate, the conjugated enzyme retained 68.2% of its original activity after incubation at 70 °C for 30 min which was 1.4-fold higher than that retained by the native enzyme (50.3%) under the same conditions. The Kd value at 80 °C for the dextran conjugated α-amylase was 2.5-fold lower than that of the native enzyme. Dextran conjugated α-amylase was more resistance against the inhibitors than the native enzyme, and retained 70.6% of its activity in presence of 10 mM CuSO4, while the native form retained only 34.1%.