Color development upon reaction of ferric ion with the toxin JSTX, a glutamate receptor blocker present in the venom gland of the spider Nephila clavata (Joro spider).

A spider toxin, JSTX, derived from Nephila clavata, which blocks glutamate receptor was found to react with Fe3+. Mechanism of the coloration may be chelate formation since the green color completely faded upon the addition of EDTA. The colored JSTX significantly lost its neurophysiological activity. This unique coloration may be useful for not only detecting specific blockers of the glutamate receptor in spider venom but also for characterizing the glutamate receptor.