Aspartate aminotransferase from Eleusine coracana, a C4 plant: purification, characterization, and preparation of antibody

Aspartate aminotransferase (AspAT) isozymes from Eleusine coracana (an NAD-malic enzyme type C4 plant) were examined. Three groups of isoenzymes were identified (AspAT-1, AspAT-2, and AspAT-3). AspAT-1 (localized in the mesophyll cells) and AspAT-3 (localized in the bundle sheath cells), both of which are considered to function in the C4 acid pathway, were purified and their kinetic and physical properties studied. Both isoenzymes had a molecular mass of 80 kDa and were shown to consist of two identical 40-kDa monomers. Except for the higher affinity for aspartate and the lower activity for the forward direction (Asp----OAA) at lower pH exhibited by AspAT-3 compared with AspAT-1, the isozymes had similar kinetic properties. However they had quite different isoelectric points. Polyclonal antibodies raised against AspAT-3 preferentially cross-reacted with AspAT-3 but did show some cross-reactivity with AspAT-1.