Characterisation of alpha-amylase inhibitor from Streptomyces xinghaiensis AAI2 in solid substrate

Abstract

Alpha-amylase inhibitors, which play metabolic roles in the organisms that produce them, by impeding the activity of alpha-amylase enzyme, have been isolated from many sources including plants and microorganisms. They vary in characteristics and applications based on their sources though there are characters that appear similar despite the source. Alpha-amylase inhibitor was produced by Streptomyces xinghaiensis AAI2 cultured on wheat bran substrate supplemented with a nutrient basal medium which was also used to adjust both the moisture content (73%) and initial pH (6.48) of the medium. The extract obtained was purified using standard purification techniques (ammonium sulphate precipitation, dialysis and column chromatography). Characteristics such as effects of pre-incubation and pH, total protein, specific activity, total activity, percentage yield, molecular weight and kinetics were determined. The alpha-amylase inhibitor produced was found to occur in isoforms having molecular weights of 14.2 and 56 kDa. Total protein, specific activity and percent yield obtained were 0.19 mg/mL, 745.11 AIU and 2.27% respectively. The optimum activity was obtained at pH 8.0 and in the presence of Cobalt and Calcium ions while pre-incubation for 10 min was best with no further improvement in the activity beyond this time. The inhibitor exerted a non-competitive type of inhibition.

Keywords

• Alpha-amylase inhibitor
• Non-competitive inhibition
• Isoform
• Solid state fermentation