Figure 8

Synthesis of (A) amylose and (B) an amylopectin cluster in the endosperm. Starch synthase I (SSI): catalyzes the synthesis of elongated amylopectin chains with the degree of polymerization (DP) of approximately 6–7, to form chains of DP 8–12. SSII-a: catalyzes the synthesis of elongated amylopectin chains of DP 6–10 to DP 12–25. SSIII catalyzes the synthesis of long amylopectin chains of DP 25–35 or greater. Starch-branching enzyme I (SBEI) plays an important but not exclusive role in the synthesis of B1-, B2-, and B3 chains. SBEII-b performs a distinct function in the formation of A-chains. Debranching enzymes (DBEs) remove unnecessary or erroneous branches.