Thiemann, Volker and Dönges, Catharina and Prowe, Steffen G and Sterner, Reinhard and Antranikian, Garabed (2004) Characterisation of a thermoalkali-stable cyclodextrin glycosyltransferase from the anaerobic thermoalkaliphilic bacterium Anaerobranca gottschalkii. Archives of microbiology 182 (2-3), pp. 226-35.
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The thermoalkaliphilic anaerobic bacterium Anaerobranca gottschalkii produces an extracellular CGTase when grown on starch at 55 degrees C and pH 9.0. The gene encoding this CGTase was cloned and successfully expressed in Escherichia coli. It encodes a protein consisting of 721 amino acids with a signal sequence of 34 amino acids. On SDS-polyacrylamide gels, the purified CGTase from A. gottschalkii displayed the expected molecular mass of 78 kDa. The recombinant enzyme was purified with a yield of 13.5% and displayed a specific activity of 210 units/mg. This CGTase, which represents the first report of a CGTase from an anaerobic thermoalkaliphile, was active at a broad range of temperature and pH, namely 55-70 degrees C and pH 5-10. It completely converted amylose, amylopectin and native starch to cyclodextrins, preferentially alpha-cyclodextrin. With a longer incubation period, the alpha-cyclodextrin to beta-cyclodextrin ratio declined. Variations in substrate type and concentration influenced the product pattern. Increasing the substrate concentration (0.5-20.0%) and glucans containing branching points (alpha-1,6 glycosidic linkages) shifted the product pattern to: beta-cyclodextin > alpha-cyclodextrin > gamma-cyclodextrin. In addition to these cyclodextrins, larger cyclodextrins (>8 glucose units) were formed in the initial reaction period. The CGTase was stabilised against thermal inactivation by calcium ions and high substrate concentrations; and 5 mM of CaCl(2) shifted the apparent melting point of the enzyme from 60 degrees C to 69 degrees C.
|Institutions:||Biology, Preclinical Medicine > Institut für Biophysik und physikalische Biochemie > Prof. Dr. Reinhard Sterner|
|Subjects:||500 Science > 570 Life sciences|
|Refereed:||Yes, this version has been refereed|
|Created at the University of Regensburg:||Yes|
|Deposited On:||15 Apr 2010 07:53|
|Last Modified:||15 Apr 2010 07:53|
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