title: Phosphorylation of C6- and C3-positions of glucosyl residues in starch is catalysed by distinct dikinases.
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.
authors.affiliation: Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, Building 20, 14476 Potsdam-Golm, Germany. ritte@rz.uni-potsdam.de
authors.forename: Gerhard
authors.initials: G
authors.lastname: Ritte
authors.forename: Matthias
authors.initials: M
authors.lastname: Heydenreich
authors.forename: Sebastian
authors.initials: S
authors.lastname: Mahlow
authors.forename: Sophie
authors.initials: S
authors.lastname: Haebel
authors.forename: Oliver
authors.initials: O
authors.lastname: Kötting
authors.forename: Martin
authors.initials: M
authors.lastname: Steup
mesh_terms: D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D005936:Glucans / Q000737:chemistry / Q000378:metabolism*; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010766:Phosphorylation; D017866:Phosphotransferases (Paired Acceptors) / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013213:Starch / Q000737:chemistry / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D005936:Glucans; D011994:Recombinant Proteins; D013213:Starch; D017866:Phosphotransferases (Paired Acceptors); D005947:Glucose