In enzymology, a phosphoglucan, water dikinase is an enzyme that catalyzes the chemical reaction The 3 substrates of this enzyme are ATP, phospho-alpha-glucan, and H2O, whereas its 3 products are AMP, O-phospho-[phospho-alpha-glucan], and phosphate. This enzyme belongs to the family of transferases, to be specific, those transferring phosphorus-containing groups (phosphotransferases) with paired acceptors (dikinases). The systematic name of this enzyme class is ATP:phospho-alpha-glucan, water phosphotransferase. Other names in common use include PWD, and OK1.