On the role of histidine residues in cyclodextrin glycosyltransferase: chemical modification with diethyl pyrocarbonate.
Ethoxyformylation with diethyl pyrocarbonate of approximately 1.5 His residues per molecule of enzyme reduced the cyclising activity of both the alpha-cyclodextrin glycosyltransferase from Klebsiella pneumoniae strain M 5 al and the beta-cyclodextrin glycosyltransferase from Bacillus circulans strain 8 by greater than 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 alpha CD 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.
Bender
H
H
Institut für Organische Chemie und Biochemie, Universität Freiburg i. Br., F.R.G.
D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology; D001665:Binding Sites; D004047:Diethyl Pyrocarbonate; D005964:Glucosyltransferases / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry; D007711:Klebsiella pneumoniae / Q000201:enzymology; D008969:Molecular Sequence Data
D006639:Histidine; D005964:Glucosyltransferases; C019963:cyclomaltodextrin glucanotransferase; D004047:Diethyl Pyrocarbonate