C. botulinum produces the toxin as a complex of proteins, among which is the neurotoxic moiety. The toxin is synthesized as a relatively inactive single-chain polypeptide with a molecular weight of ~150 kDa. It becomes an active toxin by selective proteolytic cleavage to yield the heavy and light chains that are linked by a single disulphide bond and non-covalent interactions. The toxin’s light chain is a Zn++-containing endopeptidase that blocks acetylcholine-containing vesicles from fusing with the terminal membrane of the motor neuron, resulting in flaccid muscle paralysis