罗伊氏乳杆菌葡萄糖基转移酶的生化特性及催化行为初探

Biochemical characteristics and catalytic behavior of Lactobacillus reuteriglucosyltransferase

葡萄糖基转移酶(glucosyltransferase,GTase)是一类可将α-1,4糖苷键转化为其他糖苷键的重要酶类,经其改性后得到的产物可作为一种新型的膳食纤维。该研究对来源于罗伊氏乳杆菌的葡萄糖基转移酶基因进行了异源表达,并对纯化后的GTase进行酶学性质分析及功能研究。结果表明,GTase的分子质量为105 kDa,在pH 7.0~8.5之间很稳定,4℃下保存12 h,残余酶活力仍保持在80%以上。最适温度和最适pH分别为40℃和5.0,在此条件下加入Ca^(2+),可使酶活力提高约2.1倍。最适反应条件下,GTase对麦芽糊精(DE12)的K_(m)和V_(max)分别为(1.18±0.21)g/L和2.6μg/s。麦芽糊精(DE12)经GTase在40℃反应72 h,产物中α-1,6糖苷键的提高了38.4%,易消化淀粉的含量降低了25.96%,慢消化淀粉及抗消化淀粉的含量分别提高了8.97%和17.76%。

Glucosyltransferase(GTase)is a kind of important enzyme which can convertα-1,4 glycosidic bond into other glycosidic bond.The modified product can be used as a new type of dietary fiber.The glucosyltransferase gene from Lactobacillus reuteri was heterologously expressed.The purified GTase was analyzed for its enzymatic properties and function.The results showed that the molecular weight of GTase is 105 kDa,the enzyme was stable at pH 7.0-8.5,the residual enzyme activity remained above 80%after being stored at 4℃for 12 h.The optimum temperature and pH were 40℃and 5.0 respectively.Under these conditions,Ca^(2+)could increase the enzyme activity by about 2.1-fold.The K_(m)and V_(max)of GTase to maltodextrin(DE12)were(1.18±0.21)g/L and 2.6×10^(-6) g/s respectively.When maltodextrin(DE12)was reacted with GTase at 40℃for 72 h,the content ofα-1,6 glycosidic bond was increased by 38.4%,the content of rapidly digestible starch was decreased by 25.96%,the content of slowly digestible starch and resistant starch were increased by 8.97%and 17.76%respectively.