Changes in cytosolic Mg2+ levels can regulate the activity of the plasma membrane H+-ATPase in maize.
Plant PM (plasma membrane) H+-ATPase, a major consumer of cellular ATP, is driven by the MgATP complex which may dissociate at low cytosolic Mg2+ activity. We investigated whether hydrolytic activity of PM H+-ATPase is inhibited at ATP concentrations exceeding the Mg2+ concentration. Activity in isolated maize PMs was measured at pH 6.5 in the presence of 5 mM Mg2+ (high) or 2 mM Mg2+ (low), whereas K+ was applied at concentrations of 155 mM (high) or 55 mM (low). In all experiments, with membrane vesicles either from roots or leaves, the enzyme activity decreased in the presence of Mg2+-free ATP. At inhibitory ATP concentrations, the activity was not influenced by the K+ concentration. The activity was restored after increasing the Mg2+ concentration. ATP inhibition also occurred at pH 7.5. Kinetic modelling shows that Mg2+-free ATP acted as a competitive inhibitor with a Ki in the range of the Km. Ki decreased by 75% at low K+ concentration. Ki was one order of magnitude lower at pH 7.5 compared with pH 6.5. The observed inhibition is consistent with a concept in which down-regulation of the cytosolic Mg2+ activity is involved in (phyto)hormonal stress responses.
Institute of Plant Nutrition, Justus Liebig University, 35392 Giessen, Germany. stefan.m.hanstein@ernaehrung.uni-giessen.de
Stefan
S
Hanstein
Xiaozhi
X
Wang
Xiaoqing
X
Qian
Peter
P
Friedhoff
Ammara
A
Fatima
Yuhua
Y
Shan
Ke
K
Feng
Sven
S
Schubert
D000255:Adenosine Triphosphate / Q000378:metabolism; D001667:Binding, Competitive; D055162:Biocatalysis; D002462:Cell Membrane / Q000201:enzymology*; D025222:Chloroplast Proton-Translocating ATPases / Q000378:metabolism; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008954:Models, Biological; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000201:enzymology / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D015398:Signal Transduction; D003313:Zea mays / Q000201:enzymology* / Q000378:metabolism*
D010940:Plant Proteins; D000255:Adenosine Triphosphate; D025222:Chloroplast Proton-Translocating ATPases; D017506:H(+)-K(+)-Exchanging ATPase; D006180:Proton-Translocating ATPases; D008274:Magnesium; D011188:Potassium