An Immunological Study of Rat Acetylcholinesterase: Comparison with Acetylcholinesterases from Other Vertebrates

Abstract

We have examined the immunoreactivity of acetylcholinesterase from different vertebrate species with a rabbit antiserum raised against the purified rat brain hydrophobic enzyme (G₄ form). We found no significant interaction with enzymes from Electrophorus, Torpedo, chicken, and rabbit. The antiserum reacted with acetylcholinesterases from the brains of the other mammalian species studied, with titers decreasing in the following order: rat = mouse > human > bovine. The serum was inhibitory with murine and human acetylcholinesterases, but not with the bovine enzyme. The inhibition was partially depressed in the presence of salt (e.g., l M NaCl). In those species whose acetylcholinesterase was recognized by the antiserum, both soluble and detergent-soluble fractions behaved in essentially the same manner, interacting with the same antibodies. The apparent immunoprecipitation titer was decreased in the presence of salt, and it did not make any difference whether NaCl was included in the solubilization procedure or added to the extracts. Both G₁ and G₄ forms of acetylcholinesterase in the soluble and delergent-soluble fractions were recognized by the antiserum, and in the case of the human enzyme, by monoclonal antibodies produced against human erythrocyte acetylcholinesterase. However, the monomer G₁ showed a clear tendency to form smaller complexes and precipitate less readily than the tetramer' G₄. Athough we cannot exclude the existence of significant differences belween the various molecular forms of acelylcholinesterase, our results are consistent with the hypothesis that they all derive from the same gene or set of genes by postlranslalional modifications.