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Changes of membrane‐associated Mg 2+ ‐activated ATPase of cucumber roots during calcium starvation
Author(s) -
Matsumoto Hideaki,
Kawasaki Toshio
Publication year - 1981
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1981.tb02714.x
Subject(s) - atpase , enzyme , enzyme assay , calcium , biochemistry , chemistry , enzyme activator , biology , organic chemistry
The properties of membrane‐associated ATPase of cucumber ( Cucumis sativus cv. Seiriki No. 2) roots cultured in a complete medium (complete enzyme) and in a medium lacking Ca 2+ (Ca 2+ ‐deficient enzyme) were investigated. The basal activity of membrane‐associated ATPase increased during Ca 2+ starvation, while Mg 2+ ‐activation of the enzyme decreased and even resulted in inhibition by high Mg 2+ concentration at the late stage of the Ca 2+ starvation. The complete enzyme had low basal activity and showed a Mg 2+ ‐activated hyperbolic reaction curve in relation to ATP concentration. Ca 2+ ‐deficient enzyme with high basal activity showed a biphasic reaction curve and Mg 2+ ‐activation was seen only at high ATP concentrations. Activation of membrane‐associated ATPase by various cations was decreased or lost during Ca 2+ starvation. The basal ATPase activity of Ca 2+ ‐deficient enzyme increased for various substrates including pyrophosphate, p‐nitrophenyl phosphate, glucose‐6 phosphate, β‐glycerophosphate, AMP, ADP and ATP. Mg 2+ ‐activation was found only for ADP and ATP in both the complete and Ca 2+ ‐deficient enzymes, but the activation for ATP was greatly reduced by Ca 2+ starvation. The heat inactivation curves for basal and Mg 2+ ‐activated ATPase did not differ much between the complete and Ca 2+ ‐deficient enzyme. The delipidation of membrane‐associated enzyme by acetone affected the protein content and the basal activity slightly, but inhibited the Mg 2+ ‐activated ATPase activity clearly with somewhat different behaviour between the complete and Ca 2+ ‐deficient enzyme.