acid-phosphatase and beticolin-1

Beticolin-1 and beticolin-2, yellow toxins produced by the phytopathogenic fungus Cercospora beticola, inhibit the plasma membrane H(+)-ATPase. Firstly, since beticolins are able to form complexes with Mg2+, the role of the beticolin/Mg2+ complexes in the inhibition of the plasma membrane proton pump has been investigated. Calculations indicate that beticolins could exist under several forms, in the H(+)-ATPase assay mixture, both free or complexed with Mg2+. However, the percentage inhibition of the H(+)-ATPase activity is correlated to the concentration of one single form of beticolin, the dimeric neutral complex Mg2H2B2, which appears to be the active form involved in the H(+)-ATPase inhibition. Secondly, since previous data suggested that beticolins could also be active against other Mg2(+)-dependent enzymes, we tested beticolin-1 on the vacuolar H(+)-PPase, which requires Mg2+ as co-substrate, and on the alkaline and acid phosphatases, which do not use Mg2+ as co-substrate. Only vacuolar H(+)-PPase is sensitive to beticolin-1, which suggests that beticolins are specific to enzymes that use a complex of Mg2+ as the substrate. The same Mg2H2B2 complex which is responsible of the plasma membrane H(+)-ATPase inhibition appears to be also involved in the inhibition of the vacuolar H(+)-PPase.

Topics: Acid Phosphatase; Alkaline Phosphatase; Biological Transport, Active; Cell Membrane; Enzyme Inhibitors; Heterocyclic Compounds, 4 or More Rings; Inorganic Pyrophosphatase; Magnesium; Mycotoxins; Proton-Translocating ATPases; Pyrophosphatases; Vacuoles; Zea mays