Table I. Arabidopsis genes encoding enzymes and other proteins involved in starch degradation.
Only 10 out of 27 identified starch-related degrading proteins are required for nighttime leaf starch metabolism. Of the remainder, some are inactive; others have acquired specialized functions in other tissues and/or conditions, and in some cases are extraplastidial. N.A. Not applicable.
| Enzyme/Transporter | EC Number | Reaction Catalyzed | No. of Isoforms | Required for Nighttime Leaf Starch Degradation | Not Essential for Nighttime Leaf Starch Degradation |
|---|---|---|---|---|---|
| Glucan water dikinase | EC 2.7.9.4 | Transfer of β-phosphate of ATP to glucosyl residues of starch | 3 | GWD1, PWD | GWD2 |
| Phosphoglucan phosphatase | EC 2.7.9.5 | Hydrolysis of starch-bound phosphate | 3 | SEX4, LSF1 | LSF2 |
| β-Amylase | EC 3.2.1.2 | Exoamylase, hydrolytic cleavage of α-1,4-glucosidic bonds liberating β-maltose | 9 | BAM3, BAM4 | BAM1, BAM2, BAM5-BAM9 |
| α-Amylase | EC 3.2.1.1 | Endoamylase, hydrolytic cleavage of α-1,4-glucosidic bonds liberating linear and branched oligosaccharides | 3 | – | AMY1–AMY3 |
| Debranching enzyme | EC 3.2.1.68 | Hydrolytic cleavage of α-1,6-glucosidic bonds releasing linear oligosaccharides | 2 | ISA3 | LDA |
| Glucan phosphorylase | EC 2.4.1.1 | Phosphorolytic cleavage of α-1, 4-glucosidic bonds liberating Glc-1-P (Glc1P) and inorganic phosphate (Pi) | 2 | – | PHS1, PHS2 |
| Disproportionating enzyme | EC 2.4.1.25 | Glucanotransferase, transfers maltosyl units from one 1,4-α-glucan to another, liberating Glc | 2 | DPE1, DPE2 | – |
| Maltose transporter | N.A. | Maltose exchange facilitator between plastid and cytosol | 1 | MEX1 | – |
| Glc transporter | N.A. | Glc exchange facilitator between plastid and cytosol | 1 | – | GlcT |
| Putative Glc1P/Pi translocator | N.A. | Putative counter exchange of Glc1P and Pi between plastid and cytosol (both directions) | 1 | – | Glc1PT |
| Total number | 27 | 10 | 17 |