The biochemistry of botulinum toxin type B.

Botulinum toxin type B (BTX-B) is a member of a family of neurotoxins produced by the anaerobic bacteria Clostridium botulinum. BTXs specifically inhibit acetylcholine release at the neuromuscular junction and cause muscle paralysis in humans. The mechanism of action of BTXs involves inactivation of the neural exocytotic pathway by proteolytic cleavage of components of the exocytotic apparatus. Purified BTXs have been used clinically to treat disorders of muscle contraction, such as spasticity and dystonia. BTXs are purified as high molecular weight complexes that contain additional bacterial proteins which function to protect the toxin molecule. BTX complexes are stable in solution only at acidic pH. A new method was developed to purify intact BTX-B complexes. The resulting liquid formulation of high specific activity BTX-B (Elan's BTX-B evaluated as NeuroBloc) is buffered at pH 5.6 and demonstrates long-term stability at 2 to 25 degrees C.