Cyclodextrin glucanotransferases not only transform starch into cyclodextrins, but also catalyze the transfer of cyclodextrins to appropriate acceptors and the disproportionation of linear dextrins. These three reactions are manifestations of a single catalytic activity. The transfer of a-cyclodextrin to maltitol as well as the disproportionation of functionalized dextrins carrying maltitol at the reducing end are studied in the presence of the cyclodextrin glucanotransferase of Klebsiella pneumoniae. The transfer reaction is a fast process followed by the disproportionation of the primary product. The primary functionalized dextrin is degraded in the presence of excess acceptor mostly by the exchange of maltose units. Studies on the disproportionation of purified functionalized linear dextrins reveals that the acceptor is the most prominent product. Apparently, disproportionation leads to the synthesis of starch. [on SciFinder (R)]