FIGURE 7.

Model for the enzymatic steps in starch degradation in Arabidopsis leaf mesophyll chloroplasts. A, depiction of the starch granule surface with double helices (inset) aligned in crystalline lamellae. B, phosphorylation of glucan chains by GWD1 and PWD, solubilizing the crystalline lamellae. C, β-amylolysis of glucan chains by BAM3 and BAM1 until a phosphate or a branch point is reached. D, SEX4 and LSF2 dephosphorylate glucan chains. E, ISA3 and LDA hydrolyze branch points of stubs left by the BAMs. F, AMY3 liberates small linear and branched glucan chains.