Cyclodextrin glycosyltransferases from Klebsiella pneumoniae M 5 al and Bacillus macerans: quantitative analysis by high-performance liquid chromatography of the (1 leads to 4)-alpha-D-glucopyranosyl transfer-products from some linear and cyclic substrates

Branched saccharides formed by the action of His-modified cyclodextrin glycosyltransferase from Klebsiella pneumoniae M 5 al on starch

Digestion of potato starch with His-modified alpha-cyclodextrin glycosyltransferase from Klebsiella pneumoniae M 5 al yielded branched tetra- to nona-saccharides, as revealed by debranching with pullulanase. Maltose and maltotriose stubs preponderated together with small proportions of D-glucose stubs. The branched saccharides accounted for approximately 1.2% of the starch.

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.

Studies of the mechanism of the cyclisation reaction catalysed by the wildtype and a truncated alpha-cyclodextrin glycosyltransferase from Klebsiella pneumoniae strain M 5 al, and the beta-cyclodextrin glycosyltransferase from Bacillus circulans strain 8

The actions of the wildtype and a truncated alpha-cyclodextrin glycosyltransferase from Klebsiella pneumoniae strain M 5 al on malto-oligosaccharides showed no significant differences, and there was marked dependence of the kinetic parameters on the chain lengths of the substrate. The action of the beta-cyclodextrin glycosyltransferase from Bacillus circulans was less dependent on the chain length of the substrate, but Vmax of the initial cyclisation with the longer malto-oligosaccharides was only 28% of that determined for the enzyme of K. pneumoniae. The rate parameters suggested that the active site of each enzyme spans nine glucosyl residues, and that the catalytic sites are situated between subsites three and four for the K. pneumoniae enzymes and between subsites two and three for the B. circulans enzyme. The molecular binding affinities and the affinities of the 9th subsite were calculated from the rate parameters. The primary and tertiary structures of alpha-amylases and cyclodextrin glycosyltransferases are compared in the context of the reaction mechanism of the latter enzymes.

Studies of the inhibition by malto-oligosaccharides of the cyclisation reaction catalysed by the cyclodextrin glycosyltransferase from Klebsiella pneumoniae M 5 al with glycogen

The substrate qualities of malto-oligosaccharides for the disproportionation reaction catalysed by the cyclodextrin glycosyltransferase [(1----4)-alpha-D-glucan:[(1----4)-alpha-D-glucopyranosyl]transferase (cyclising) EC 2.4.1.19] from Klebsiella pneumoniae M 5 al have been re-investigated. Maltose failed to be homologised with measurable velocity. The initial rates of disproportionation and the affinities of the enzyme increased with the chain lengths of the substrates. Maltopentaose was the smallest saccharide which, by disproportionation, yielded longer chains being cyclised initially. D-Glucose did not affect the initial cyclisation from glycogen, but served as acceptor for the "chain-shortening" reaction. Maltose inhibited the initial cyclisation reaction in a linearly competitive manner. Maltotriose and maltotetraose inhibited the cyclisation reaction competitively, the inhibition kinetics pointing to the binding of two effector-molecules to the enzyme. Competitive inhibition was also found with malto-pentaose, -hexaose, and -heptaose. The degrees of inhibition increased from maltose to maltotetraose, and decreased with the larger saccharides; maltotriose and maltotetraose were the most effective inhibitors of the initial cyclisation. Some possibilities for the subsite-mechanisms are discussed.