PLANT PHYSIOLOGY , Vol 111, Issue 3 773-779, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Cercospora beticola Toxins (X. Inhibition of Plasma Membrane H+-ATPase by Beticolin-1)
F. Simon-Plas, E. Gomes, M. L. Milat, A. Pugin and J. P. Blein
Laboratoire de Phytopharmacie, Institut National de la Recherche Agronomique/Universite de Bourgogne UA692, bv 1540, 21034 Dijon Cedex, France
Beticolin-1 is a toxin produced by the fungus Cercospora beticola. The
chemical structure of this toxin was previously elucidated. The effects of
beticolin-1 on purified corn root plasma membrane H+-ATPase were studied in
a solubilized form or were reconstituted into liposome membranes. The ATP
hydrolysis activity of the purified solubilized enzyme was inhibited by
micromolar concentrations of beticolin-1, and this inhibition was
noncompetitive with respect to ATP. When this purified enzyme was inserted
into liposome membranes, a competitive inhibition of the H+-ATPase
hydrolysis activity by beticolin-1 was observed. The effect of beticolin-1
on the formation of H+-ATPase-phosphorylated intermediate was also studied.
With the purified enzyme in its solubilized form, the level of
phosphorylated intermediate was not affected by the presence of
beticolin-1, whereas micromolar concentrations of the toxin led to a marked
inhibition of its formation when the enzyme was reconstituted into
liposomes. These data suggest that (a) the plasma membrane H+-ATPase is a
direct target for beticolin-1, and (b) the kinetics of inhibition and the
effect on the phosphorylated intermediate are linked and both depend on the
lipid environment of the enzyme.
