Cercospora beticola toxins. X. Inhibition of plasma membrane H+-ATPase by beticolin-1.

摘要

The effects of beticolin-1 (a toxin produced by the fungus Cercospora beticola) on purified maize cv. Mona 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 non-competitive with respect to ATP. When the 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 notaffected 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. It is suggested that the plasma membrane H+-ATPase is a direct target for beticolin-1, and that the kinetics of inhibition and the effect on the phosphorylated intermediate are linked and both depend on the lipid environment of the enzyme.