The monoclonal antibody MAC252 does not react with the (-) enantiomer of abscisic acid.

An RIA procedure has been developed for ABA quantification using MAC62, a monoclonal antibody raised against (+)-cis, trans -ABA. This widely used method now relies on MAC252, a recloned version of the exhausted MAC62. Recently, it has been suggested that MAC252 was not able to discriminate between the (+) and (-) enantiomers of ABA. As this can be misleading when interpreting RIA results, it has been carefully examined here whether MAC252 reacts with (-)-ABA. MAC252 exhibited negligible cross-reactivity with (-)-ABA, which was confirmed with commercial mixtures of ABA isomers. It is concluded that the RIA protocol can continue to be used with MAC252 as it was with MAC62.