Bafilomycin A1 is a non-competitive inhibitor of the tonoplast H+-ATPase of maize coleoptiles
1994
White, P.J.
When microsomal membranes from maize (Zea mays L. cv. Clipper) coleoptiles were separated by isopycnic centrifugation on a continuous 10-45% sucrose gradient, bafilomycin A1-inhibited ATPase activity co-localized with the activities of the tonoplast marker-enzymes, nitrate-inhibited ATPase and K+-dependent pyrophosphatase. Thus, bafilomycin A1 is a specific inhibitor of the vacuolar H+-ATPase of maize coleoptiles. Inhibition of the vacuolar H+-ATPase by bafilomycin A1 was strictly dependent upon the concentration of the enzyme present in the assay medium, suggesting a stoichiometric association between bafilomycin A1 and the vacuolar H+-ATPase. In tonoplast-enriched preparations, half-maximal inhibition was obtained at 43 pmol bafilomycin A1 mg-1 protein. Bafilomycin A1 inhibited the vacuolar H+-ATPase in a simple non-competitive manner: increasing bafilomycin A1 concentrations reduced the Vmax of the H+-ATPase, but had no effect on its Km towards ATP.
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