Monoclonal Antibodies to Rabbit Brain Acetylcholinesterase: Selective Enzyme Inhibition, Differential Affinity for Enzyme Forms, and Cross‐Reactivity with Other Mammalian Cholinesterases

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Abstract
Eleven unique monoclonal IgG antibodies were raised against rabbit brain acetylcholinesterase (AChE, EC 3.1.1.7), purified to electrophoretic homogeneity by a 2-step procedure involving immunoaffinity chromatography. The apparent dissociation constants of these antibodies for rabbit AChE ranged from about 10 nM to more than 100 nM (assuming 1 binding site/catalytic subunit). Species cross-reactivity was investigated with crude brain extracts from rabbit, rat, mouse cat, guinea-pig and human. One antibody bound rabbit AChE exclusively; most bound AChE from 3 or 4 species; 2 bound enzyme from all species tested. Identical, moderate affinity for rat and mouse brain AChE was displayed by 2 antibodies; 2 others were able to distinguish between these similar antigens. Nine of the antibodies had lowered affinity for AChE in the presence of 1 M NaCl, but 2 were salt resistant. Analysis of mutual interferences in AChE binding suggested that certain of the antibodies were competing for nearby epitopes on the AChE surface. One antibody was a potent AChE inhibitor (IC50 [median inhibitory concentration dosage] = 10-8 M), blocking up to 90% of the enzyme activity. Most of the antibodies were less able to bind the readily soluble AChE of detergent-free brain extracts than the AChE which required detergent for solubilization. The extreme case, an antibody that was unable to recognize nearly half of the soluble AChE, was suspected of lacking affinity for the hydrophilic enzyme form.