PLANT PHYSIOLOGY , Vol 113, Issue 1 163-174, Copyright © 1997 by American Society of Plant Biologists
|
BIOCHEMISTRY AND ENZYMOLOGY |
Sterol Modulation of the Plasma Membrane H+-ATPase Activity from Corn Roots Reconstituted into Soybean Lipids
A. Grandmougin-Ferjani, I. Schuler-Muller and M. A. Hartmann
Institut de Biologie Moleculaire des Plantes, du Centre National de la Recherche Scientifique, 28 rue Goethe, 67083 Strasbourg Cedex, France
A partially purified H+-ATPase from the plasma membrane (PM) of corn (Zea
mays L.) roots was inserted into vesicles prepared with soybean (Glycine
max L.) phospholipids and various concentrations of individual sterols
using either a freeze-thaw sonication or an octylglucoside dilution
procedure. Both methods yielded a functional enzyme that retained its
native characteristics. We have investigated the effects of typical plant
sterols (i.e. sitosterol, stigmasterol, and 24-methylcholesterol) on both
ATP hydrolysis and H+ pumping by the reconstituted corn root PM ATPase. We
have also checked the influence of cholesterol and of two unusual sterols,
24-methylpollinastanol and 14[alpha],24-dimethylcholest-8-en-3[beta]-ol.
Here we present evidence for a sterol modulation of the plant PM H+-ATPase
activity. In particular, cholesterol and stigmasterol were found to
stimulate the pump, especially when present at 5 mol%, whereas all of the
other sterols tested behaved as inhibitors at any concentration in
proteoliposomes. In all situations H+ pumping was shown to be more
sensitive to a sterol environment than was ATP hydrolysis. Our results
suggest the occurrence of binding sites for sterols on the plant PM
H+-ATPase.
