Characterization of plasma membrane bound cation stimulated atpase isolated from the roots of cucumis sativus
Canadian Journal of Botany 66(7): 1470-1473
ISSN/ISBN: 0008-4026 DOI: 10.1139/b88-202
A membrane fraction enriched with Mg2+- or Mn2+-dependent, monovalent cation stimulated ATPase was isolated from cucumber roots (Cucumis sativus L.) by an aqueous two-polymer phase system of Dextran T500 (6.5%, w/w) and polyethylene glycol (PEG) 3350 (6.5%, w/w) at pH 7.8. The ATPase activity associated with the upper PEG-rich fraction (plasma membrane) was characterized. The optimum pH for the activation by Mg2+ and Mn2+ was in the range 5.8-6.0. The activity was substrate specific for ATP. Kinetics with Mg2+ or Mn2+ followed a simple Michaelis-Menten relationship. The apparent Km for Mg2+ activation (0.60 mM) of the ATPase was about twice that of the apparent Km for Mn2+ (0.38 mM). ATPase was stimulated by monovalent cations and showed an order of cation preference of K+ > Na+ > Rb+ = NH4+ > Li+ > choline. Calcium inhibited the plasma membrane ATPase, apparently by a direct interaction with ATPase rather than by disrupting the MgATP2- complex.