Purification and amino acid composition of type A botulinum neurotoxin

A method to purify type A botulinum neurotoxin from a 64 liter bacterial culture is reported. The procedure includes cation exchange chromatography at pH 7.0. The final product, essentially homogeneous (according to polyacrylamide gel-sodium dodecylsulfate electrophoresis), is a mixture of two forms of the neurotoxin (mol. wt 145,000); the dichain or nicked form (over 95%) and its precursor the single chain or unnicked form. Two batches of the neurotoxin purified by the method described here and one batch purified according to the method of Sugii and Sakaguchi were similar in purity and amino acid composition. The best estimate of the number of amino acid residues per neurotoxin molecule (mol. wt 145,000) is: Asp200Thr75Ser79Glu114Pro44Gly64Ala53Val70CyS10Met22Ile111Leu104Tyr71 Phe68Lys100His14Arg43Trp17.