Studies of the degradation of pullulan by the decycling maltodextrinase of Flavobacterium sp.

Abstract

The mode of action on pullulan of the decycling maltodextrinase of Flavobacterium sp. was studied. The enzyme specifically split (1 → 4)-α- d-glucosidic linkages and, preferentially through cleavage of its tetraose units, degraded the α- d-glucan into larger fragments, which were further hydrolysed. About 39% of the carbohydrate was found to be the branched trisaccharide panose, established by 1H NMR spectroscopy and by the mp of the corresponding alditol dodecaacetate. At concentrations > 56 mM, panose exhibited product inhibition of further hydrolysis. Remarkable amounts of a dimer and a tetramer of panose, and of a branched tetrasaccharide, 6 3- O-α- d-glucosylmaltotriose, that arose from the tetraose units and the reducing ends of the pullulan molecules, were found among the larger hydrolysis products. The probable structures of some minor fragments were deduced from the debranching pattern obtained with pullulanase. The formation of glucose (6% of the carbohydrate) observed during pullulan degradation was most probably due to multiple transglycosylation reactions between the branched tetrasaccharide and a branched pentasaccharide, with subsequent splitting off of glucose from the transglycosylation products.