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Adenosine Triphosphatase from Soybean Callus and Root Cells

Department of Biology, University of Houston, Houston, Texas 77004

The ATPase activity of a membrane fraction from soybean (Glycine max L.) root and callus cells, presumed to be enriched in plasma membrane, has been characterized with respect to ion stimulation, pH requirement, and nucleotide specificity. The enzyme from both sources was activated by divalent cations (Mg²⁺ > Mn²⁺ > Zn²⁺ > Ca²⁺ > Sr²⁺) and further stimulated by monovalent salts. Preparations from root cells were stimulated by monovalent ions according to the sequence: K⁺ > Rb⁺ > Choline⁺ > Na⁺ > Li⁺ > NH₄⁺ > Cs⁺ > tris⁺. Membrane preparations from callus cells showed similar stimulatory patterns except for a slight preference for Na⁺ over K⁺. No synergism between K⁺ and Na⁺ was found with preparations from either cell source.

The pH optimum for ATP hydrolysis in the presence of 50 mM KCl and 3 mM MgSO₄ was 6.5 for both preparations and slightly higher in the presence of 3 mM MgSO₄ alone. The order of nucleotide preference was found to be: ATP >> ADP > GTP > CTP > UTP. Maximal glucan synthetase activity at high (1 mM), but not at low (1 µM), substrate was found to be coincident with the position of this fraction on the sucrose gradient.