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Planta. 2003 Mar;216(5):798-801. Epub 2002 Nov 9.

Determination of the starch-phosphorylating enzyme activity in plant extracts.

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Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25 Haus 20, 14476 Golm, Germany.


For quantification of alpha-glucan, water dikinase (GWD) activity in crude extracts of plant tissues a radio-labeling assay was established that uses soluble starch and (33)P-labeled ATP as phosphate acceptor and donor, respectively. A constant rate of starch labeling was observed only if the ATP applied was labeled at the beta position. In wild-type extracts from leaves of Arabidopsis thaliana (L.) Heynh. the maximum rate of starch phosphorylation was approximately 27 pmol min(-1) (mg protein)(-1). Leaf extracts from the GWD-deficient sex1 mutants of Arabidopsis showed no significant incorporation of phosphate whereas extracts from potato (Solanum tuberosum L.) tuber expressing a GWD antisense construct exhibited less activity than the wild-type control. To our knowledge this is the first time that a quantification of the starch-phosphorylating activity has been achieved in plant crude extracts.

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