Monoclonal antibodies to the α- and β-subunits of the plant mitochondrial F₁-ATPase

We have generated nine monoclonal antibodies against subunits of the maize (Zea mays L.) mitochondrial F₁-ATPase. These monoclonal antibodies were generated by immunizing mice against maize mitochondrial fractions and randomly collecting useful hybridomas. To prove that these monoclonal antibodies were directed against ATPase subunits, we tested their cross-reactivity with purified F₁-ATPase from pea cotyledon mitochondria. One of the antibodies (α-ATPaseD) cross-reacted with the pea F₁-ATPase α-subunit and two (β-ATPaseD and β-ATPaseE) cross-reacted with the pea F₁-ATPase β-subunit. This established that, of the nine antibodies, four react with the maize α-ATPase subunit and the other five react with the maize β-ATPase subunit. Most of the monoclonal antibodies cross-react with the F₁-ATPase from a wide range of plant species. Each of the four monoclonal antibodies raised against the α-subunit recognizes a different epitope. Of the five β-subunit antibodies, at least three different epitopes are recognized. Direct incubation of the monoclonal antibodies with the F₁-ATPase failed to inhibit the ATPase activity. The monoclonal antibodies α-ATPaseD and β-ATPaseD were bound to epoxide-glass QuantAffinity beads and incubated with a purified preparation of pea F₁-ATPase. The ATPase activity was not inhibited when the antibodies bound the ATPase. The antibodies were used to help map the pea F₁-ATPase subunits on a two-dimensional map of whole pea cotyledon mitochondrial protein. In addition, the antibodies have revealed antigenic similarities between various isoforms observed for the α- and β-subunits of the purified F₁-ATPase. The specificity of these monoclonal antibodies, along with their cross-species recognition and their ability to bind the F₁-ATPase without inhibiting enzymic function, makes these antibodies useful and invaluable tools for the further purification and characterization of plant mitochondrial F₁-ATPases.