Tryptophan Residues of Bacillus Cycloamylose Glucanotransferase: Effect of Modification with N-Bromosuccini-mide on the Enzyme-catalysed Synthesis of Cyclomaltoheptaose from Maltotriose

Cycloamylose glucanotransferase(cyclomalto-oligosaccharide glu-canotransferase, CGTase), obtained from Bacillus stearotheromophilus, was found to catalyze the synthesis of cyclomalto-oligosaccharides from maltotriose (G₃) as a substrate. The synthetic reaction is one of the CGTase-catalysed reactions, so called “cyclisation”. A main saccharide produced by the cyclisation reaction under the experimental conditions employed was confirmed to be cyclomaltoheptaose CG₇. The kinetic parameters, the Michaelis constant Km and the molar activity k₀ were evaluated for the cyclisation reaction. Modification of tryptophan residues with N-bromosuccinimide (NBS) was found to effect on Km, but not on k₀ of the cyclisation reaction, suggesting that the tryptophan residue (Trp⁹⁷) carries an essential role in the binding (disproportionation process) of maltotriose.