Changes of membrane associated magnesium activated atpase of cucumber cucumis sativus roots during calcium starvation
Matsumoto, H.; Kawasaki, T.
Physiologia Plantarum 52(4): 442-448
ISSN/ISBN: 0031-9317 DOI: 10.1111/j.1399-3054.1981.tb02714.x
The properties of membrane-associated ATPase of cucumber (C. sativus cv. Seiriki No. 2) roots cultured in a complete medium (complete enzyme) and in a medium lacking Ca2+ (Ca2+-deficient enzyme) were investigated. The basal activity of membrane-associated ATPase increased during Ca2+ starvation, while Mg2+-activation of the enzyme decreased and even resulted in inhibition by high Mg2+ concentration at the late stage of the Ca2+ starvation. The complete enzyme had low basal activity and showed a Mg2+-activated hyperbolic reaction curve in relation to ATP concentration. Ca2+-deficient enzyme with high basal activity showed a biphasic reaction curve and Mg2+-activation was seen only at high ATP concentrations. Activation of membrane-associated ATPase by various cations was decreased or lost during Ca2+ starvation. The basal ATPase activity of Ca2+-deficient enzyme increased for various substrates including pyrophosphate, p-nitrophenyl phosphate, glucose-6-phosphate, .beta.-glycerophosphate, AMP, ADP and ATP. Mg2+-activation occurred only for ADP and ATP in both the complete and Ca2+-deficient enzymes, but the activation for ATP was greatly reduced by Ca2+ starvation. The heat inactivation curves for basal and Mg2+-activated ATPase did not differ much between the complete and Ca2+-deficient enzyme. The delipidation of membrane-associated enzyme by acetone affected the protein content and the basal activity slightly, but inhibited the Mg2+-activated ATPase activity clearly with somewhat different behavior between the complete and Ca2+-deficient enzyme.