malfunction |
analysis of changes in GWD protein abundance in relation to starch levels in wild-type plants, in transgenic plants in which GWD transcripts are strongly reduced by induction of RNA interference, and in transgenic plants overexpressing GWD, overview. Overexpression of GWD does not accelerate starch degradation in leaves, and starch degradation is not inhibited until GWD levels are reduced by 70%. GWD protein levels do not vary over the diel cycle and the protein has a half-life of 2 days. Plants expressing redox-insensitive GWD have normal starch turnover |
Arabidopsis thaliana |
metabolism |
the first step on the pathway of starch degradation in Arabidopsis thaliana leaves at night is the phosphorylation of starch polymers, catalyzed by glucan, water dikinase, GWD. The enzyme exerts only a low level of control over starch degradation in Arabidopsis leaves. The starch-phosphorylating enzymes are attractive candidates for the control of flux through starch degradation. Daily control of starch degradation is likely to be at a posttranslational level |
Arabidopsis thaliana |
physiological function |
enzyme GWD is a subject to redox regulation. A disulfide bond can be reduced in vitro by micromolar concentrations of reduced thioredoxins, resulting in activation of the enzyme. Enzyme GWD in the soluble fraction of plant extracts is in the reduced form, but a fraction of the enzyme bound to starch granules is reported to be in an oxidized, inactive form. Enzyme GWD has a long half-life and a low flux control coefficient for starch degradation. Transcriptional regulation of GWD protein levels is unlikely to be important for the control of starch degradation |
Arabidopsis thaliana |