title: Cercospora beticola Toxins (X. Inhibition of Plasma Membrane H+-ATPase by Beticolin-1).
abstract: 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.
authors.affiliation: Laboratoire de Phytopharmacie, Institut National de la Recherche Agronomique/Universite de Bourgogne UA692, bv 1540, 21034 Dijon Cedex, France.
authors.forename: F.
authors.initials: F
authors.lastname: Simon-Plas
authors.forename: E.
authors.initials: E
authors.lastname: Gomes
authors.forename: M. L.
authors.initials: ML
authors.lastname: Milat
authors.forename: A.
authors.initials: A
authors.lastname: Pugin
authors.forename: J. P.
authors.initials: JP
authors.lastname: Blein