Microsomal membranes from Cicer arietinum (chick-pea) roots contained an ATP phosphohydrolase activity that could be solubilized by high-ionic-strength media. The enzyme has been purified to homogeneity by affinity and ion-exchange chromatography. It has the properties of an ATP diphosphohydrolase (apyrase, EC 3.6.1.5) that hydrolyses different nucleoside di- and tri-phosphates but has no activity towards monophosphoric esters and pyrophosphate. No stimulation by K+ could be demonstrated for either the membrane-bound or the purified enzyme, and therefore it would seem not to be related to the K+ -dependent ATPase postulated to mediate K+ transport in plants.
