Abstract
Ethoxyformylation with diethyl pyrocarbonate of ∼ 1.5 His residues per molecule of enzyme reduced the cyclising activity of both the α-cyclodextrin glycosyltransferase from Klebsiella pneumoniae strain M 5 al and the β-cyclodextrin glycosyltransferase from Bacillus circulans strain 8 by >90%. Pre-incubation with substrate protected the enzymes from ethoxyformylation. Digestion of starch by the modified enzymes resulted in a delayed formation of cyclodextrins (cyclomalto-oligosaccharides, CDs), but a marked increase in the production of reducing saccharides. Similarly, coupling of αCD and maltose and successive disproportionation yielded mainly glucose and malto-oligosaccharides. The results are discussed in the context of the role of conserved His residues for binding of substrate and the transfer reactions.
Published Version
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