Modification ofα-Amylase by Sodium Alginate

Abstract

Sodium alginate, activated by periodate oxidation, was covalently linked to porcine pancreatic α-amylase via reductive alkylation with NaBH 4 . The enzyme-polymer conjugate, purified by gel filtration on Fractogel EMD BioSEC (S), retained about 50% of the native specific amylolytic activity. The sugar content was estimated to be 712 mol of monosaccharides per mol of enzyme protein. An average of 11 amino groups out of 21 groups from α-amylase were modified with the polysaccharide. The functional stability was improved for α-amylase after conjugation with sodium alginate. In comparison with the native enzyme, the thermostability of α-amylase was increased by this modification. In addition, the stability in the range of pH 5.0-11.0 was improved for the modified enzyme. The conjugate was also more resistant to denaturation by 0.3% sodium dodecylsulphate, retaining about 10% of its initial activity after 120 min of incubation. The formation of stabilizing salt bridges in the protein surface of the α-amylase-polysaccharide complex was confirmed by FT-IR spectrometry. Attending to the results obtained, we conclude that the covalent attachment of the anionic polysaccharide sodium alginate to the enzymes might be a useful and non-expensive method for improving the stabilization of these biocatalysts under various denaturing conditions.