Photolabile derivatives of maltose and maltotriose as ligands for the affinity labelling of the maltodextrin-binding site in porcine pancreatic alpha-amylase.

The 3-azibutyl group was linked through sulfur to the anomeric position of maltose and maltotriose to yield the photolabile thioglycosides 3-azibutyl 1-thio-alpha-maltoside (11) and 3-azibutyl 1-thio-alpha-maltotrioside (12), and to the 4'- and 6'-position of maltose to give the thioethers 4'-S-(3-azibutyl)-4'-thiomaltose (8) and 6'-S-(3-azibutyl)-6'-thiomaltose (15). All four compounds were good competitive inhibitors of the action of porcine pancreatic alpha-amylase. Compound 12 irreversibly deactivated the enzyme to approximately 100% when irradiated together with the protein. The other compounds were much less effective. It is likely that separate areas of the enzyme binding site are chemically modified by the different ligands.