Characterization and Multiple Applications of a Highly Thermostable and Ca2+-Independent Amylopullulanase of the Extreme Thermophile Geobacillus thermoleovorans

摘要

The amylopullulanase of Geobacillus thermoleovorans NP33 (apu105) is Ca2+-independent with a molecular mass of 105 kDa and optimum activity at 80 degrees C and pH 7.0. The apu105 is extremely thermostable with T-1/2 of 7.8 h at 90 degrees C and hydrolyzes starch, pullulan, and malto-oligosaccharides, but not panose and cyclodextrins. The low Km values of apu105 (starch, pullulan, amylose, and amylopectin) indicates higher affinity of apu105 than others. The action of the enzyme on mixed substrates (starch and pullulan) confirmed the presence of only one active site for cleaving both alpha-1,4- and alpha-1,6- glycosidic linkages. The raw starches are efficiently hydrolyzed into glucose, maltose, and malto-oligosaccharides. Two-step starch saccharification involving pretreatment with apu105 followed by glucoamylase enhanced glucose yield. The supplementation of whole wheat dough with apu105 markedly enhanced the loaf volume, shelf-life, and the texture of bread. The enzyme is compatible with detergents and useful in desizing of cotton fabrics.