Abstract
The glucansucrases synthesize glucan by a two-site mechanism in which the glucose and the growingg glucan are covalently attached to the active site. The glucose is transferred to the reducing end of the growing glucan chain by an insertion mechanism in which glucose is inserted between the enzyme and the growing chain. The chain is released from the active-site by acceptor reactions . When the acceptor is a glucan chain, a branch linkage is formed. When the acceptor is a low molecular weight carbohydrate, the glucan chain is released with the acceptor attached to the reducing end, and a low molecular weight acceptor product is produced with a glucose residue attached to the acceptor . With many acceptors, the acceptor product is an acceptor itself and a series of acceptor-products are produced. The structure of the acceptor product depends on the structure of the acceptor and the particular glucansucrase. Acceptors divert glucose away from the synthesis of glucan and terminate glucan synthesis. The amount and the number of acceptor products varies, depending on the concentration ratio of acceptor to sucrose. At low acceptor to sucrose ratios, the yield of acceptor-products is low and at high ratios, the yields are high, and the amount of dextran is higher at low ratios and lower at high ratios. With acceptors that form a homologous series of acceptor-products (e .g., maltose), a low ratio gives a relatively large number of acceptor-products (≥10) and a high ratio gives a small number of acceptor-products (1-2) in high yields with respect to sucrose.
