To understand the role of His and Glu in the catalytic activity of Bacillus licheniformis α-amylase (BLA), His235 was replaced with Glu. The mutant enzyme, H235E, was characterized in terms of its mode of action using labeled and unlabeled maltooctaose (Glc8). H235E predominantly produced maltotridecaose (Glc13) from Glc8, exhibiting high substrate transglycosylation activity, with Km=0.38mM and kcat/Km=20.58mM(-1)s(-1) for hydrolysis, and Km2=18.38mM and kcat2/Km2=2.57mM(-1)s(-1) for transglycosylation, while the wild-type BLA exhibited high hydrolysis activity exclusively. Glu235-located on a wide open groove near subsite +1-is likely involved in transglycosylation via formation of an α-1,4-glycosidic linkage and may recognize and stabilize the non-reducing end glucose of the acceptor molecule.
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