Characterization of a Ca2+‐translocating ATPase from corn root microsomes

Abstract

Brauer, D., Schubert C. and Tu, S,‐I. 1990. Characterization of a Ca2+‐translocating ATPase from corn root microsomes. ‐ Physiol. Plant. 78: 335‐344.The existence of a Ca2+‐translocating ATPase in microsomes from maize (Zea mays L. cv, WF9 × Mo17) roots was evaluated using assays to follow Ca2+‐stimulation of ATP hydrolysis and Ca2+ transport by changes in the fluorescence of chlorotetracycline, ATP hydrolysis by microsomes was stimulated by the addition of Ca2+ and further enhanced by the Ca ionophore A23187 and bovine brain calmodulin only in the presence of Ca2+, Stimulation by these agents was additive and sensitive to vanadate. These results were consistent with the presence of a Ca2+‐translocating ATPase in microsomal membranes. The fluorescence of chlorotetracycline in the presence of microsomes and Ca2+ increased upon the addition of ATP, indicating the transport of Ca2+, The initial rate and extent of change in fluorescence were stimulated by calmodulin and quenched by the addition of either A23187 or EGTA, but not by protonophores. Changes in chlorotetracycline fluorescence were prevented by vanadate. Therefore, results using chlorotetracycline also indicated the presence of a Ca2+‐translocating ATPase, Localization experiments indicated that the majority of the Ca2+‐translocating ATPase was on the endoplasmic reticulum.