Comparative characterization of raw starch hydrolyzing α-amylases from various Bacillus strains

Two saccharifying α-amylases with different molecular masses were purified from Bacillus subtilis IFO 3108. The higher molecular mass α-amylase 1 (RBSA-1, MM 67 kDa) was able to adsorb to α-cyclodextrin (α-CD) sepharose CL-6B and hydrolyze raw starch. RBSA-1 showed weak adsorption to raw corn starch over the wide pH range of 5.0–9.0. At low pH (5.0–6.0), RBSA-1 exhibited high adsorption to raw potato starch. The lower molecular mass α-amylase 2 (BSA-2, MM 45 kDa) exhibited enzymatic properties similar to RBSA-1, however, was unable to adsorb to α-CD sepharose CL-6B and failed to hydrolyze raw starch. On the other hand, a liquefying type α-amylase (RBLA), purified from Bacillus sp., exhibited remarkable adsorption to raw starches tested over a wide pH range (5.0–9.0). This pH range corresponded to that suitable for the digestion of raw starches. The adsorption of RBSA-1 and RBLA to α-CD sepharose CL-6B was pH-independent, however, the extent of adsorption of RBSA-1 (70–85%) was much greater than that of RBLA (30–45%). The hydrolysis of raw corn starch was specifically inhibited by α-CD for both enzymes. The Ki value (0.44 mM) for RBSA-1 was much lower than that for RBLA (3.44 mM).