Starch branching enzyme from cassava Manihot esculenta Crantz tubers

Abstract

Starch branching enzyme (SBE, EC 2.4.1.18) from cassava Manihot esculenta Crantz tubers was found in the parenchymal tissue. It was purified by precipitation with 10 % polyethylene glycol (PEG) followed by column chromatography on DEAE-cellulose, Q-Sepharose and Sephadex G-200, respectively. SBE was purified up to 148.5 folds with 2.0 % yield. The molecular weights of the enzyme determined by sodium dodecyl sulfate -polyacrylamide gel electrophoresis (SDS-PAGE) was 80 kD and the molecular weight by Sephadex G-200 column was 160 kD, indicating the enzyme may contain 2 identical subunits. The optimum pH of the enzyme activity was 7.0, optimum temperature was 37°C and its pi was 5.4. Moreover, enzyme activity increased by 5.7, 2.4, 2.0 and 1.9 folds when 1.0 mg/ml solution of starch, glycogen, amylopectin or dextrin were presence in the reaction mixture respectively. The enzyme was found to be stable up to 45°C. At -20°C 50 % activity was retained at 4week storage.