Production and Characterization of Monoclonal Antibodies against Aspartate Aminotransferase-P(2) from Lupin Root Nodules

Twenty-one monoclonal antibodies were raised against the aspartate aminotransferase-P₂ isoenzyme from root nodules of Lupinus angustifolius L.] cv Uniharvest. Induction of this isoenzyme is positively correlated with the onset of N₂ fixation in effective root nodules and is associated with the assimilation of ammonia by the plant in the Rhizobium-legume symbiosis. The monoclonal antibodies produced were all of the IgG class, recognized five different epitopes on the protein, and represented greater than 90% of the available epitopes. These epitopes were not unique to lupin nodule aspartate aminotransferase-P₂ but were shown to be present on the enzyme from tobacco leaves and potato. Four of the epitopes were conformational with a fifth epitope recognized by the appropriate monoclonals in both its native and denatured forms. None of the monoclonal antibodies produced reacted with Rhizobium Iupini NZP2257 extracts. Antibodies against two epitopes showed some cross-reaction with the constitutive aspartate aminotransferase-P₁ isoenzyme also found in lupin root nodules. However, affinity of these monoclonals for AAT-P₁ was three orders of magnitude lower than for AAT-P₂. Monoclonals against the other epitopes appeared to be specific for aspartate aminotransferase-P₂.