Structure and Regulation of Enzymes for the Degradation and Resynthesis of Glycogen

were inhibited by epoxyalkyl oligo-l,4-~-~-glucosides. Cellotriosides were better inhibitors than cellobiosides; variation of the alkyl chain showed a maximum of inhibition rate with the n-pentyl residue. This probably places the epoxy group in a position corresponding to the glucosyl oxygen of the next glucose residue. The large dissociation constant of the enzyme-inhibitor complex formed before the covalent inhibition indicated that glucose-binding sites probably exist on the reducing side of the bond to be cleaved. Here too the covalent reaction is catalysed by an acidic group at the active site that protonates the epoxide and makes it more reactive. Substrate analogues with an epoxide function have been found to be the most effective inhibitors for glycosidases. To a large extent this is due to their protonation at the active site by an acid, which converts the epoxide to a highly reactive species. They are thus another example of k,,,. inhibitors as defined by Rando (1974).