Adenosine Triphosphatase from Soybean Callus and Root Cells

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Abstract
The ATPase activity of a membrane fraction from soybean (Glycine max L.) root and callus cells, presumed to be enriched in plasma membrane, was 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 ATP .mchgt. ADP > GTP > CTP > UTP. Maximal glucan synthetase activity at high (1 mM) but not at low (1 .mu.M), substrate was coincident with the position of this fraction on the sucrose gradient.