Abstract
α-1, 4-Glucan lyase (EC 4.2.2.13) produces 1, 5-anhydro D-fructose from α-1, 4-linked glucose oligomers and polymers, such as maltose, maltosaccharides, starch and glycogen. It is a single polypetide enzyme with a molecular mass around 120 kDa and a pH optimum of pH 4.0-6.5. The lyase is highly specific toward α-1, 4-glucosidic bonds and shows negligible activity toward α-1, 6-glucosidic bonds. It is an exo-acting enzyme and starts its cleavage from the non-reducing end, converting the glucose units to 1, 5-anhydrofructose until the last glucose unit on the reducing end is reached or a branching point is met. Thus with maltose as substrate glucose and 1, 5-anhydrofructose are formed in an equimolar basis, while with amylopectin or glycogen as the substrate it generates 1, 5-anhydrofructose and a limit dextrin that is rich in α-1, 6-branches. At present the lyase has been purified and cloned from fungi and algae. The occurrence of 1, 5-anhydrofructcse and its further metabolite 1, 5-anhydro-D-glucitol in E. coli and mammals may indicate the operation of this alternative glycogen degradation pathway in these organisms.
