Chemical modification of taipoxin and the consequences for phospholipase activity, pathophysiology, and inhibition of high-affinity choline uptake.

Treatment of taipoxin with p-bromophenacyl bromide resulted in modification of single histidine residues in the alpha and beta subunits. The modification decreased the neurotoxicity (lethality) 350-fold, but the inhibitory action on high-affinity choline transport was reduced only threefold. The phospholipase activity and Ca2+-association constants for taipoxin and its subunits were determined. A model for the neurotoxicity of taipoxin indicates the alpha subunit as the ultimate cause of the disruption of synaptic transmission.