Monovalent Ion Stimulated Adenosine Triphosphatase From Oat Roots

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Abstract
Monovalent ion stimulated ATPase activity from oat (Avena sativa) roots has been found to be associated with various membrane fractions (cell wall, mitochondrial and microsomal) of oat roots. The ATPase requires Mg2+ (or Mn+2) but is further stimulated by K+ and other monovalent ions. The monovalent ions are ineffective in the absence of the divalent activating cation. The ATPase has been described with respect to monovalent ion specificity, temperature, pH, substrate specificity, and Mg2+ and K+ concentrations. It was further shown that oligomycin inhibits a part of the total ATPase activity and on the basis of the oligomycin sensitivity it appears that at least 2 membrane associated ATPases are being measured. The mitochondrial fraction is most sensitive to oligomycin and the microsomal fraction is least sensitive to oligomycin. The oligomycin insensitive ATPase appears to be stimulated more by K+ than the oligomycin sensitive ATPase. It was further shown that per gram fresh weight of roots, approximately 0.7 to 0.8 μmoles of K+ were absorbed per μmole of K+ stimulated ATP hydrolysis. This result was obtained for a variety of K+ concentrations and was taken to mean that sufficient membrane associated ATPase exists to account for K+ transport in the oat roots.