Fine Structure of Amylopectin

Abstract

Starch granules consist of two major polyglucans, namely, branched amylopectin and essentially linear amylose. In all nonmutant starches, amylopectin is the major component and is responsible for the internal structure of starch granules, which is the native, semicrystalline form of starch. The granules, irrespective of the plant source, consist of granular rings of alternating amorphous and semicrystalline polymers. On a smaller scale, blocklets as well as crystalline and amorphous lamellae have been identified. Amylopectin is generally accepted as the contributor to the lamellar structure, but the nature of blocklets is only beginning to be resolved. Amylopectin consists of numerous chains of glucosyl units that are divided into short and long chains. These chains are organized as clusters that have been isolated by using endo-acting enzymes, and the fine structure of the clusters have been investigated. The clusters consist of still smaller, tightly branched units known as building blocks. The organization of the clusters and building blocks in the macromolecular structure of amylopectin is to date uncertain, and two schools exist at present suggesting that amylopectin either has a treelike branched cluster structure or a building block backbone structure. The structural features of amylopectin and the two models presently in debate are discussed in this chapter.

Systems Genetics Identifies a Novel Regulatory Domain of Amylose Synthesis

“…Amylose is made up of a long helical homopolymer of D-Glc units linked together by a-1,4 glycosidic bonds with occasional branching at a-1,6 branch points (Hanashiro, 2015). Amylopectin is a highly branched polymer of short a-1,4-linked D-Glc units with reducing ends interlinked by a-1,6-glycosidic bonds that form a very large native biopolymer that is up to two orders-of-magnitude bigger than amylose (Bertoft, 2015). These two components are arranged in alternating crystalline and amorphous lamellae to form starch granules (Vandeputte and Delcour, 2004).…”

Comparison of Chain-Length Preferences and Glucan Specificities of Isoamylase-Type α-Glucan Debranching Enzymes from Rice, Cyanobacteria, and Bacteria

“…Secondly, the capacity of DBE for debranching the DP2 and DP3 chains was examined by using the β-LD of rice amylopectin because the glucan includes maltosyl- and maltotriosyl-chains as its external chain segments [ 6 , 59 ]. Both CytISA and EcoGlgX could liberate only the DP3 chains, but not the DP2 chains, of the β-LD ( Fig 11B ).…”

“…The distinct fine structure of amylopectin has been characterized by the fact that it is composed of the tandem-linked clusters, a structural unit of amylopectin, with a fixed size of approximately 9 nm [ 4 – 6 ], while glycogen has no such structural features. The involvements of DBEs in amylopectin synthesis have been proposed from extensive studies with maize [ 7 – 12 ], rice [ 13 – 19 ], potato [ 20 , 21 ], barley [ 22 ], Arabidopsis [ 23 – 29 ], Chlamydomonas [ 30 – 33 ], and a Cyanobacterium sp.…”

Starch Properties Affecting Maltose Production Ability in Vegetable Black Soybean Seeds (Edamame) with Different Maturation Periods

“…Starch granules are composed of alternating crystalline and amorphous lamellae. The crystalline lamellae are composed of double helices formed by amylopectin side chains (approximately DP 12-16), and the amorphous lamellae have a branched structure (Bertoft, 2015). It is known that the longer the double helices of the side chains are, the higher the stability of the crystalline lamellae, and that highly crystalline starch exhibits a high gelatinization temperature.…”