Abstract
Extracellular cyclodextrin glucanotransferase (CGTase, K.F.2.1.19) was characterized for the first time in a strain of bacteria of the species Caldalkalibacillus mannanilyticus IB-OR17-B1. The enzyme was isolated from the culture supernatant using ultrafiltration and affinity adsorption on corn starch. The specific activity of the CGTase was increased in 18-fold as a result of purification with the enzyme yield 56%. The molecular mass of the purified enzyme was 70 kDa according to the denaturing electrophoresis in polyacrylamide gel. The CGTase of C. mannanilyticus IB-OR17-B1 demonstrated a maximal cyclizing activity under pH 8 and temperature 60°C, respectively, and it was stable in the pH range 7–10 and temperatures ≤70°C. The thermal stability of the enzyme under 70°C increased by 10–15% in the presence 5–10 mM of calcium and magnesium salts. The cations of Ag+, Cu2+, Zn2+, Fe2+ and Fe3+ in concentration 5 mM inhibited a CGTase activity by 90, 26, 23, 18 and 11%, respectively. The purified CGTase under optimal conditions and enzyme-substrate ratio 1 U/g converted a potato starch during 24 h to mixture of α-, β- and γ-cyclodextrins with mass ratio 38.8 : 52.6 : 8.6 and yield 42%.
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