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  • Title: Phosphorylation of C6- and C3-positions of glucosyl residues in starch is catalysed by distinct dikinases.
    Author: Ritte G, Heydenreich M, Mahlow S, Haebel S, Kötting O, Steup M.
    Journal: FEBS Lett; 2006 Sep 04; 580(20):4872-6. PubMed ID: 16914145.
    Abstract:
    Glucan, water dikinase (GWD) and phosphoglucan, water dikinase (PWD) are required for normal starch metabolism. We analysed starch phosphorylation in Arabidopsis wild-type plants and mutants lacking either GWD or PWD using (31)P NMR. Phosphorylation at both C6- and C3-positions of glucose moieties in starch was drastically decreased in GWD-deficient mutants. In starch from PWD-deficient plants C3-bound phosphate was reduced to levels close to the detection limit. The latter result contrasts with previous reports according to which GWD phosphorylates both C6- and C3-positions. In these studies, phosphorylation had been analysed by HPLC of acid-hydrolysed glucans. We now show that maltose-6-phosphate, a product of incomplete starch hydrolysis, co-eluted with glucose-3-phosphate under the chromatographic conditions applied. Re-examination of the specificity of the dikinases using an improved method demonstrates that C6- and C3-phosphorylation is selectively catalysed by GWD and PWD, respectively.
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