In general, the optimum pH for alpha-amylase varies between 2 and 12.The optimum pH for fungi and bacteria –amylase is generally in the acidic and neutral range, for example, the optimum pH for bacillus –amylase is 3, and the optimum pH for alkaline -amylase is generally between 9 and 12. In addition, temperature and calcium ions affect the optimum pH of some alpha-amylase and change its optimum range of action.The optimum operating temperature of -amylase from different microbial sources also varies greatly, among which the optimum operating temperature is as low as 25℃-30℃ and as high as 100℃-130℃.In addition, calcium ions and sodium ions also have a certain effect on the optimum temperature of some enzymes (Pandey,2000; Vihinen and Mantsala, 1989; Ogasahara etc., 1970; Chary and Reddy,1985).
Alpha-amylase is a metalzyme, which is inhibited by many metal ions, especially heavy metal ions. In addition, the sulfhydryl group, N-bromosuccinic acid, P-hydroxymercury benzoic acid, iodoacetic acid, BSA, EDTA and EGTA had significant inhibitory effects on -amylase. Among them, alpha-amylase contains at least one Ca2+, Ca2+ can maintain the appropriate conformation of the enzyme molecule, thus maintaining its maximum activity and stability.Ca2+ is more affinitive to -amylase than other ions, with a number of binding calcium ions between 1 and 10. In general, the stability of -amylase in the presence of Ca2+ is better than that in the absence of Ca2+, but alpha-amylase has also been reported to be inactivated in the presence of Ca2+, while it remains active after EDTA treatment. In addition, Ca2+ has also been reported to have no effect on -amylase (Mamo,1999; Kundu and Das, 1970; Laderman et al.,1993).
When alpha-amylase ACTS on starch, the viscosity of solution decreases gradually and the reducing force increases gradually as the reaction progresses. At the same time, as the concentration of substrate decreases, the concentration of product increases, and the enzyme may be partially inactivated, finally leading to a gradual decrease in the reaction rate until the reduction force is no longer increased. At this time, the hydrolysis rate is called the \”hydrolysis limit\”.The hydrolysis limit of -amylase from different sources is also different. Generally, the hydrolysis rate of -amylase is 40%-50%, but the hydrolysis rate of Aspergillus Niger ATCC15475 can reach 95%-100%, and the hydrolysis rate of Endosporium -amylase can reach 90%. The products are all glucose. When bacillus subtilis saccharified -amylase ACTS on soluble starch, the hydrolysis rate reaches over 70%, while the hydrolysis rate of the liquefactive -amylase produced by Bacillus starch liquefaction is only 30%.
In addition, there are some differences in the properties of -amylase from different sources. Fungi and bacteria -amylase are mainly used in industry. At present, alpha-amylase has been widely used in many industries, such as feed, modified starch and starch sugar, baking industry, beer brewing, alcohol industry, fermentation and textile, etc. It is an important industrial enzyme.
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