Salt-Stimulated Adenosine Triphosphatases from Carrot, Beet, and Chara Australis

Abstract

Soluble adenosine triphosphatases (ATPases) from carrot, beetroot, and the fresh-water alga Chara australis were activated by sodium and potassium chlorides, but not by choline chloride, and were inhibited by potassium sulphate and fluoride. Ouabain was not inhibitory, and Na+-K+ synergism of the type found with animal "transport" ATPases was not observed, The ATPases had acid pH optima and were not activated by Mg2+; fractionation on Sephadex and electrophoresis in starch gel gave identical patterns of ATPase activity (with or without potassium chloride) and acid phosphatase. The identity of the salt-stimulated ATPases with acid phosphatase was supported by parallel inhibition by trypan blue and adenylyl methylene diphosphonate and by association of the activities during purification. Enzyme eluted from carrot cell-wall fractions at high ionic strength was indistinguishable from the soluble enzyme. Cell walls freed of enzyme with alkali took up the ATPase from a soluble preparation of carrot enzyme. Trypan blue at a concentration (14 [mu][image]) causing marked inhibition of salt-stimulated ATPase did not inhibit potassium chloride uptake in aged carrot slices. The specificity of salt stimulation and the possible involvement of salt-stimulated ATPase in active transport of salt into plant cells is discussed.