title: Biochemical characterisation of a glycogen branching enzyme from Streptococcus mutans: Enzymatic modification of starch.
abstract: A gene encoding a putative glycogen branching enzyme (SmGBE) in Streptococcus mutans was expressed in Escherichia coli and purified. The biochemical properties of the purified enzyme were examined relative to its branching specificity for amylose and starch. The activity of the approximately 75kDa enzyme was optimal at pH 5.0, and stable up to 40°C. The enzyme predominantly transferred short maltooligosyl chains with a degree of polymerization (dp) of 6 and 7 throughout the branching process for amylose. When incubated with rice starch, the enzyme modified its optimal branch chain-length from dp 12 to 6 with large reductions in the longer chains, and simultaneously increased its branching points. The results indicate that SmGBE can make a modified starch with much shorter branches and a more branched structure than to native starch. In addition, starch retrogradation due to low temperature storage was significantly retarded along with the enzyme reaction.
authors.affiliation: Research Institute of Food and Nutritional Sciences, Department of Food and Nutrition, Brain Korea 21 Project, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Eun-Joo
authors.initials: EJ
authors.lastname: Kim
authors.affiliation: Research Institute of Food and Nutritional Sciences, Department of Food and Nutrition, Brain Korea 21 Project, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Soo-In
authors.initials: SI
authors.lastname: Ryu
authors.affiliation: Research Institute of Food and Nutritional Sciences, Department of Food and Nutrition, Brain Korea 21 Project, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Hyun-Ah
authors.initials: HA
authors.lastname: Bae
authors.affiliation: Research Institute of Food and Nutritional Sciences, Department of Food and Nutrition, Brain Korea 21 Project, Yonsei University, Seoul 120-749, Republic of Korea.
authors.forename: Nguyen Thi
authors.initials: NT
authors.lastname: Huong
authors.affiliation: Research Institute of Food and Nutritional Sciences, Department of Food and Nutrition, Brain Korea 21 Project, Yonsei University, Seoul 120-749, Republic of Korea. Electronic address: soobok@yonsei.ac.kr.
authors.forename: Soo-Bok
authors.initials: SB
authors.lastname: Lee
keywords: Branching reaction; Enzymatically modified starch; Glycogen branching enzyme; Retrogradation; Streptococcus mutans