Malto-oligosaccharides (MOSs) from starch conversion is advantageous for food and pharmaceutical applications. In this study, an efficient malto-oligosaccharide-forming α-amylase AmyCf was identified from myxobacterCystobactersp. strain CF23. AmyCf is composed of 417 amino acids with N-terminal 41 amino acids as the signal peptide, and conserved glycoside hydrolase family 13 (GH13) catalytic module and predicted C-terminal domain with β-sheet structure are also identified. Phylogenetic and functional analysis demonstrated that AmyCf is a novel member of GH13_6 subfamily. The special activity of AmyCf toward soluble starch and raw wheat starch is 9249 U/mg and 11 U/mg, respectively. AmyCf has broad substrate specificity toward different types of starches without requiring Ca2+. Under ideal circumstances of 60 °C and pH 7.0, AmyCf hydrolyzes gelatinized starch into maltose and maltotriose and maltotetraose as the main hydrolytic products with more than 80% purity, while maltose and maltotriose are mainly produced from the hydrolysis of raw wheat starch with more than 95% purity. The potential applicability of AmyCf in starch processing is highlighted by its capacity to convert gelatinized starch and raw starch granules into MOSs. This enzymatic conversion technique shows promise for the low-temperature enzymatic conversion of raw starch.Keywords:Malto-oligosaccharides;Cystobacter;gelatinized starch;enzymatic conversion;raw starch
To convert ginsenosides Rb1, Rb2, Rb3, and Rc into Rd by a single enzyme, a putative β-glycosidase (Pxbgl) from the xylan-degrading bacterium Petroclostridium xylanilyticum was identified and used. The kcat/Km value of Pxbgl for Rb3 was 18.18 ± 0.07 mM–1/s, which was significantly higher than those of Pxbgl for other ginsenosides. Pxbgl converted almost all Rb3 to Rd with a productivity of 5884 μM/h, which was 346-fold higher than that of only β-xylosidase from Thermoascus aurantiacus. The productivity of Rd from the Panax ginseng root and Panax notoginseng leaf was 146 and 995 μM/h, respectively. Mutants N293 K and I447L from site-directed mutagenesis based on bioinformatics analysis showed an increase in specific activity of 29 and 7% toward Rb3, respectively. This is the first report of a β-glycosidase that can simultaneously remove four different glycosyls at the C–20 position of natural PPD-type ginsenosides and produce Rd as the sole product from P. notoginseng leaf extracts with the highest productivity.
危险品化学品经营许可证（带存储）