INTERACTION BETWEEN PULLULANASE FROM KLEBSIELLA-PNEUMONIAE AND CYCLODEXTRINS

The interaction between pullulanase from Klebsiella pneumoniae and alpha-, beta-, and cyclodextrins and 6-O-alpha-glucosyl-alpha-cyclodextrin and 6-O-alpha-glucosyl-beta-cyclodextrin was examined by means of inhibition studies of the enzyme activity, UV difference spectroscopy, and flow calorimetry. All the above cyclodextrins were found to be competitive inhibitors, but beta-cyclodextrin and 6-O-alpha-glucosyl-beta-cyclodextrin showed strong inhibition, the inhibitor constants being two orders of magnitude less than those of alpha- and gamma-cyclodextrins. The difference spectra of beta-cyclodextrin were slightly but significantly different from those of the other cyclodextrins, showing blue shift of a few nanometers. Moreover, only beta-cyclodextrin has a positive entropy change upon binding with the enzyme; all the other cyclodextrins have negative values. These results show that the binding mode of beta-cyclodextrin is subtly different from those of alpha- and gamma-cyclodextrins.