The building block structure of barley amylopectin

Amylopectin branchpoints are present in amorphous lamellae of starch granules and organised into densely branched areas, referred to as building blocks. One single amylopectin cluster contains several building blocks. This study investigated the building block structure of domains (groups of clusters) and clusters in four different barley genotypes. Two of the barleys possessed the amo1 mutation, Glacier Ac38 and the double recessive SW 49427 with both wax and amo1 mutations, and were compared with the two waxy type barleys Cinnamon and Cindy. A previous detailed study on these four barley genotypes showed that the amo1 mutation affected the internal structure of amylopectin as manifested in the composition of clusters. In this work the building blocks were isolated from domains and clusters by extensive treatment with liquefying α-amylase of Bacillus subtilis and structurally characterised with enzymatic and chromatographic techniques. The proportion of large building blocks with a high number of chains was increased in the amo1 barleys, and the chain length between the blocks was short, which explained the previous findings of large clusters with more dense structure in the amo1 amylopectins.