Adenosine Triphosphatase Activity in Cell-Wall Preparations and Excised Roots of Barley

Abstract

Cell-wall preparations from barley roots contain about 20 per cent of the ATP-ase activity of the whole homogenate. This activity is maximal near pH 7, activated by calcium and magnesium ions and shows further activation when sodium and potassium chlorides are applied at alkaline pH values. High concentrations of sodium chloride and ammonium sulphate are needed to elute the activity from the walls which suggests an ionic binding with the wall fraction. Excised root tips release inorganic phosphate from ATP with no lag phase, and this activity shows a response to variation in substrate and magnesium concentration similar to that of the cell-wall preparations, suggesting a surface location of the enzyme. The properties of this hydrolytic activity are discussed in relation to those described in other plant systems and to animal transport ATP-ases.