Enzyme-catalyzed condensation reaction in a mammalian alpha-amylase. High-resolution structural analysis of an enzyme-inhibitor complex

Mammalian alpha -amylases catalyze the hydrolysis of cr-linked glucose poly mers according to a complex processive mechanism. We have determined the X- ray structures of porcine pancreatic alpha -amylase complexes with the smal lest molecule of the trestatin family (acarviosine-glucose) which inhibits porcine pancreatic alpha -amylase and yet is not hydrolyzed by the enzyme. A structure analysis at 1.38 Angstrom resolution of this complex allowed fo r a clear identification of a genuine single hexasaccharide species compose d of two alpha -1,4-linked original molecules bound to the active site of t he enzyme. The structural results supported by mass spectrometry experiment s provide evidence for an enzymatically catalyzed condensation reaction in the crystal.