Auh Joong-Hyuck, Chae Hye Young, Kim Yong-Ro, Shim Kyu-Ho, Yoo Sang-Ho, Park Kwan-Hwa
Center for Agricultural Biomaterials and Department of Food Science and Biotechnology, School of Agricultural Biotechnology, Seoul National University, Seoul 151-742, Korea.
J Agric Food Chem. 2006 Mar 22;54(6):2314-9. doi: 10.1021/jf051887r.
A cyclomaltodextrinase (CDase) isolated from alkalophilic Bacillus sp. I-5 (CDase I-5) exists in a dodecameric form, an assembly of six dimers, each catalytic site of which is located in a narrow groove at the interface of the dimeric unit. Because of the unique geometric shape of the catalytic site, the enzyme has the ability to discriminate the molecular size of substrates. An analysis of the hydrolysis reaction of the enzyme revealed that its kcat/Km value on amylose was 14.6 s(-1) (mg/mL)(-1), whereas that for amylopectin was 0.92 s(-1) (mg/mL)(-1), showing an exceptionally high preference toward amylose. CDase I-5 was applied to modify the starch structure to produce low-amylose starch products by incubating rice starch with this enzyme. We found that the amylose content of rice starch decreased from 28.5 to 9%, while the amylopectin content remained almost constant with no significant change in the side chain length distribution. When the CDase I-5-treated rice starch was stored at 4 degrees C for 7 days, the retrogradation rate was significantly retarded as compared to that in the control sample.
从嗜碱芽孢杆菌I-5中分离得到的环麦芽糊精酶（CDase I-5）以十二聚体形式存在，由六个二聚体组装而成，其每个催化位点位于二聚体单元界面处的狭窄凹槽中。由于催化位点独特的几何形状，该酶具有区分底物分子大小的能力。对该酶水解反应的分析表明，其对直链淀粉的kcat/Km值为14.6 s(-1) (mg/mL)(-1)，而对支链淀粉的kcat/Km值为0.92 s(-1) (mg/mL)(-1)，显示出对直链淀粉具有极高的偏好性。将CDase I-5应用于修饰淀粉结构，通过将水稻淀粉与该酶孵育来生产低直链淀粉淀粉产品。我们发现，水稻淀粉的直链淀粉含量从28.5%降至9%，而支链淀粉含量几乎保持不变，侧链长度分布无显著变化。当经CDase I-5处理的水稻淀粉在4℃下储存7天时，与对照样品相比，其回生速率显著减缓。
