Fine structural properties of natural and synthetic glycogens.

Glycogen, highly branched (1-->4)(1-->6)-linked alpha-d-glucan, can be extracted from natural sources such as animal tissues or shellfish (natural source glycogen, NSG). Glycogen can also be synthesized in vitro from glucose-1-phosphate using the cooperative action of alpha-glucan phosphorylase (GP, EC 2.4.1.1) and branching enzyme (BE, EC 2.4.1.18), or from short-chain amylose by the cooperative action of BE and amylomaltase (AM, EC 2.4.1.25). It has been shown that enzymatically synthesized glycogen (ESG) has structural and physicochemical properties similar to those of NSG. In this study, the fine structures of ESG and NSG were analyzed using isoamylase and alpha-amylase. Isoamylase completely hydrolyzed the alpha-1,6 linkages of ESG and NSG. The unit-chain distribution (distribution of degrees of polymerization (DP) of alpha-1,4 linked chains) of ESG was slightly narrower than that of NSG. alpha-Amylase treatment revealed that initial profiles of hydrolyses of ESG and NSG were almost the same: both glycogens were digested slowly, compared with starch. The final products from NSG by alpha-amylase hydrolysis were glucose, maltose, maltotriose, branched oligosaccharides with DP4, and highly branched macrodextrin molecules with molecular weights of up to 10,000. When ESG was digested with excess amounts of alpha-amylase, much larger macrodextrins (molecular weight>10(6)) were detected. In contrast, oligosaccharides with DP 4-7 could not be detected from ESG. These results suggest that the alpha-1,6 linkages in ESG molecules are more regularly distributed than those in NSG molecules.