A comparison of flexible and constrained haptens in eliciting antibody catalysts for paraoxon hydrolysis

A new amine-oxide hapten was employed as an antigen, producing seven monocl onal antibodies (mAbs) from a panel of 20 that catalyzed paraoxon hydrolysi s. The current hapten design differs from that previously described in that the molecule is inherently more flexible than its constrained predecessor. One of the seven antibody catalysts, mAb 1H9, showed the highest activity and was selected for detailed study. At pH = 8.77, the catalytic hydrolysis of paraoxon by mAb 1H9 followed Michaelis-Menten kinetics affording a k(ca t) = 3.73 x 10(-4) min(-1) and a K-m,= 1.12 mM with a rate acceleration k(c at)/k(uncat) = 56. The hapten was found to be a competitive inhibitor of an tibody-catalyzed paraoxon hydrolysis with a K-i,= 0.54 mM. A comparison of both the number and proficiency of antibody catalysts obtained when utilizi ng a flexible versus constrained hapten indicates that, for paraoxon hydrol ysis, constrained haptens elicit superior catalysts, suggesting that furthe r development should begin with the use of constrained haptens in producing more proficient antibody catalysts for paraoxon hydrolysis. (C) 1999 Elsev ier Science Ltd. All rights reserved.