The Mechanism of Hydrolysis of Adenosine Di - and Tri - phosphate Catalysed by Potato Apyrase By MILDRED COHN

Under suitable conditions, phosphatases generally catalyse phosphate-transfer reactions (Axelrod, 1956). When these enzymes catalyse the hydrolysis of compounds with an oxygen bridge it has been experimentally demonstrated with 180 that cleavage occurs between P and 0, as would be anticipated from the fact that they are phosphoryltransferring enzymes. By this criterion, adenosine triphosphatases, which have been shown to catalyse the cleavage ofthe bond between 0 and the terminal P (Clarke & Koshland, 1953; Cohn, 1956), may be classified as phosphoryl-transferring enzymes. In the present work, adenosine diphosphate (ADP) and adenosine triphosphate (ATP) have been hydrolysed in H2180 with a potato-apyrase preparation to determine which bond is cleaved and consequently whether the enzyme may act as a phosphoryl-transferring enzyme or as an adenyland adenosine diphosphoryl-transferring enzyme. The effect of calcium ions on the reactions has also been investigated.