THE TRANSGLYCOSYLATION REACTION OF CYCLODEXTRIN GLUCANOTRANSFERASE IS OPERATED BY A PING-PONG MECHANISM

A new photometric assay of the disproportionation activity of cyclodextrin glucanotransferase (CGTase) using 3-ketobutylidene-beta-2-chloro-4-nitrophenyl-maltopentaoside as the donor, proved that the transglycosylation reaction of CGTase was operated by a Ping-Pong Bi Bi mechanism. The values of the k(cat)/K-acceptor proved that the same configurations of free hydroxyl groups with those of D-glucopyranose at C2, C3 and C4 positions were required for the accepters used by CGTase. The structure around C6 on accepters was not essential for acceptor function, but it was recognized by CGTase, since the values of k(cat)/K-m for D-xylose were smaller than that for D-glucose. The value of k(cat)/K-m for maltose was about 20-times larger than that for D-glucose, indicating that at least two glucopyranosyl rings are recognized by the acceptor binding sites.