Preparation and properties of acetylcholinesterase from the sea mussel Mytilus edulis.

The large-scale isolation of an acetylcholinesterase from the haemolymph of the sea mussel mytilus edulis by means of fractional (NH4)2SO4 precipitation, affinity chromatography and isoelectric focusing is described. The yield is about 20% of the initial enzyme activity with a specific activity of 1727 nkat/mg protein. Purification steps are followed by disc electrophoresis, analytical isoelectric focusing and immunoelectrophoresis, showing the enzyme to be homogeneous with an isoelectric point of 4.81 +/- 0.02 and to have an apparent molecular weight of 245,000, which is composed by six equal subunits as judged by C- and N-terminal amino acid analysis. The acetylcholinesterase is a metalloprotein containing three Fe2 ions per subunit (molecular weight 40625); this consists of 351 amino acid and six sugar residues, but contains no sialic acid. As calculated from CD data, the enzyme has about 55% helical structure.