Phosphorylation of C6- and C3-positions of glucosyl residues in starch is catalysed by distinct dikinases.
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.
Ritte
Gerhard
G
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
Heydenreich
Matthias
M
Mahlow
Sebastian
S
Haebel
Sophie
S
Kötting
Oliver
O
Steup
Martin
M
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*
D029681:Arabidopsis Proteins; D005936:Glucans; D011994:Recombinant Proteins; D013213:Starch; D017866:Phosphotransferases (Paired Acceptors); D005947:Glucose