Monoclonal Antibodies to Rat Brain Acetylcholinesterase: Comparative Affinity for Soluble and Membrane-Associated Enzyme and for Enzyme from Different Vertebrate Species

Seven unique monoclonal antibodies were generated to rat brain acetylcholinesterase. Upon density gradient ultracentrifugation, immunoglobulin complexes with the monomeric enzyme appeared as single peaks of acetylcholinesterase activity with a sedimentation coefficient approximately 3S greater than that of the free enzyme. This behavior is consistent with the assumption of one binding site per enzyme molecule. Apparent dissociation constants of these antibodies for rat brain acetylcholinesterase calculated on the basis of this assumption ranged from about 10 nM to more than 1,000 nM. Some of the antibodies were less able to bind the membrane-associated enzyme that required detergent for solubilization than the naturally soluble acetylcholinesterase of detergent-free brain extracts. Species cross-reactivity was investigated with crude brain extracts from mammals (human, mouse, rabbit, guinea pig, cow, and cat) and from other vertebrates (chicken, frog, and electric eel). Three antibodies bound rat acetylcholinesterase exclusively; one had nearly the same affinity for all mammalian acetylcholinesterases investigated; the remaining three showed irregular binding patterns. None of the antibodies recognized frog and electric eel enzyme. Pooled antibody was found to be suitable for specific immunofluorescence staining of large neurons in the ventral horn of the rat spinal cord and smaller cells in the caudate nucleus. Other potential applications of these antibodies are discussed.