The goals of this work involve: (1) a more complete understanding of the mechanisms of toxicity of botulinum neurotoxins; and (2) exploration of the intracellular events leading to exocytosis. This will be accomplished by correlating inhibition of exocytosis by botulinum neurotoxic serotypes A and E to their cleavage of SNAP-25 (synaptosomal attachment protein of 25 kDa), a protein involved in exocytosis. By relating the ability of these toxins to inhibit exocytosis, their ability to cleave SNAP-25, and the functionality of SNAP-25 after exposure to botulinum neurotoxin, a better understanding of neurotoxin action and the mechanisms of exocytosis can be gained. This information may allow for better treatment for poisoning by botulinum neurotoxin, which is considered the most toxic substance on earth. It also may lead to more effective use of botulinum neurotoxin as a drug used in the treatment of a variety of spastic paralytic conditions, as well as increasing our basic understanding of the fundamental cellular process of exocytosis. Exocytosis will be measured using a well-established technique of monitoring norepinephrine release from mechanically permeabilized PC12 cells. The proteolytic cleavage of SNAP-25 in the C-terminal region by the botulinum neurotoxin will be monitored by western analysis.