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 m onoclonal antibody raised against (+)-cis, trans -ABA. This widely used met hod now relies on MAC252, a recloned version of the exhausted MAC62. Recent ly, it has been suggested that MAC252 was not able to discriminate between the (+) and (-) enantiomers of ABA. As this can be misleading when interpre ting RIA results, it has been carefully examined here whether MAC252 reacts with (-)-ABA, MAC252 exhibited negligible cross-reactivity with (-)-ABA, w hich 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 M AC62.