Selection Of Thermostable β-amylase From Soybeans And Its CDNA Expression In E.coli

β-Amylase catalyzes the liberation of β-anomeric maltose from the non-reducing ends of α-1,4-D-glucopyranosyl polymers. It is found in both plants and bacteria. Thermostable amylases are very useful in many application fields such as maltose and maltose production. High temperature can not only increase the dissolubility of starch, but also prevent the growth of bacteria, which means low cost of industry production.β-amylase activities and thermostablilities of 184 soybean cultivars were assayed in this test. We found that 5 β-amylase had more than 50% of the initial activity during a 5-hour heating period(63 ℃. pH5.0), this means they adapt to be raw material of β-amylase industry production.The cDNA clones corresponding to soybean β-amylase total RNA were isolated and sequenced. The cDNA contained an open-reading frame composed of 496 amino acids. Employing the cDNA, the recombinant β-amylase was synthesized in Escherichia coli by the expression vector pBMY. Induced by IPTG at 30°C, the recombinant β-amylase activity reached 19.61U/mL. Results show that the recombinant β-amylase can be secreted into the medium. The recombinant β-amylase had the the same optimal pH and temperature with original soybean β-amylase but a lower thermostablility.