Immobilization of α-amylase from Mung beans (Vigna radiata L.)

Abstract

α-Amylases (E.C.3.2.1.1) are enzymes that catalyzes the hydrolysis of internal α-1,4-glycosidic linkages in starch in low molecular weight products, such glucose, maltose and maltotriose units. α-Amylase from mung beans (Vigna radiata) was immobilized on sodium alginate. The pH optima of soluble α-amylase were 6, whereas that for immobilized amylase on sodium alginate was 7. Soluble amylase and sodium alginate immobilized α-amylase showed maximum activity at 40°C and 50oC, respectively. The Residual activity for free α-amylase and sodium alginate immobilized α-amylases after 50 days of storage at 37°C was found to be 18.87% and 50% respectively, whereas at 4oC, it was investigated as 45% and 65.5% for soluble and immobilized, respectively, under the same experimental conditions. The sodium alginate immobilized α-amylase showed a residual activity of 62%, after 12 uses. To study the effect of substrate concentration, the experiment was carried out by measuring the amount of product formed at different substrate concentrations. The Vmax and Km of α-amylase were derived from the Lineweaver Burke plot. The inhibiting efficiency of different heavy metals was also studied. The effect of EDTA and β-mercaptoethanol was also determined for soluble and immobilized amylase. The easy availability of mung bean α-amylase, the ease of its immobilization on low-cost matrices and good stability upon immobilization in the present study makes it a suitable product for further use in industrial applications. Mung bean α-amylase is inhibited in a competitive manner by heavy metal ions, for example, mercury with a Ki of 0.8µM. Homology modelling studies with mung bean α-amylase using barley α-amylases Amy 1 and Amy 2 as templates showed a very similar structure as expected from the high sequence identity. The model showed that α-amylase from mung beans has no sugar binding site, instead it has a methionine