Hangyan Ji,Yuxiang Bai,XiaoXiao Li,Jinpeng Wang,Xueming Xu,Zhengyu Jin
An open reading frame from Palaeococcus pacificus was discovered by genomic analysis. The recombinant PpCD was proved as novel extremely thermal-stable cyclodextrinase with potential on production of malto-oligosaccharides with specific degree of polymerization. This enzyme has extremely high substrate specificity toward cyclodextrins, while the rates of hydrolysis toward macromolecular or linear substrates such as starch, pullulan and amylose were pretty slow. The optimal pH and temperature of PpCD were determined as 6.0 and 95 °C respectively. It was confirmed that PpCD could produce malto-oligosaccharides with a certain degree of polymerization in consistent with that of cyclodextrin substrates. In this study, the preparation of high purity maltoheptaose was achieved and the suitable β-cyclodextrin concentration was about 8–10%. Therefore, PpCD may have a potential application in the production of specific degree of polymerization malto-oligosaccharides.
Xiaoxiao Li,Tong Jiang,Yu Wang,Jingjing Dong,Zhengyu Jin,Yuxiang Bai
Limosilactobacillus reuteri 121 4,6-α-glucanotransferase (GtfBΔN) modifies starch by cleaving (α1 → 4) linkages and introducing non-branched (α1 → 6) linkages to produce functional starch derivatives. Research has mainly focused on GtfBΔN converting amylose (linear substrate), whereas the conversion of amylopectin (branched substrate) has not been studied in detail. In this study, we used GtfBΔN to understand amylopectin modification and performed a set of experiments to analyze this modification pattern. The donor substrates were segments from the non-reducing ends to the nearest branch point in amylopectin as shown from the results of the chain length distribution of GtfBΔN-modified starches. Decreased and increased contents of β-limit dextrin and reducing sugars, respectively, during the incubation of β-limit dextrin with GtfBΔN indicated that the segments from the reducing end to the nearest branch point in amylopectin act as donor substrates. Dextranase was involved in the hydrolysis of the GtfBΔN conversion products of three different substrates groups, maltohexaose (G6), amylopectin, and G6 plus amylopectin. No reducing sugars were detected, therefore, amylopectin was not used as an acceptor substrate, and no non-branched (α1 → 6) linkages were introduced into it. Thus, these methods provide a reasonable and effective approach to studying GtfB-like 4,6-α-glucanotransferase in analyzing the roles and contribution of branched substrates.
危险品化学品经营许可证（带存储）