Immunological Properties of Rat Brain Choline Acetyltransferase1

Four antisera active against choline acetyltransferase (ChAc) were obtained by injecting 22 rabbits with rat brain ChAc. The ChAc preparations used for immunization (specific activity from 015 to 2 μmol/min/mg of protein) were not pure and the antisera produced were not monospecific. The antisera inhibited and precipitated ChAc, but the precipitated enzyme‐antibody complexes still retain ChAc activity. One millilitre of the most active serum precipitates 0–5 μmol/min of rat brain ChAc at the equivalence point. Its titre expressed in mg/ml of immunoglobulins precipitated with the antigen and the equivalence point was calculated at about 0.08 mg/ml of serum. This relatively low titre explains the lack of any visible ChAc immunoprecipitate in an immunodiffusion test. Cross‐reactivity studies revealed that ChAc has undergone few changes during evolution, since antisera produced against rat brain ChAc still precipitate ChAc from fish (Torpedo).