ex·o·tox·in
(ek'sō-tok'sin), A specific, soluble, antigenic, usually heat labile, injurious substance elaborated by certain gram-positive or gram-negative bacteria; it is formed within the cell, but is released into the environment where it is rapidly active in extremely small amounts; most exotoxins are proteinaceous (MW 70,000-900,000) and can have the toxic portion of the molecule destroyed by heat, prolonged storage, or chemicals; the nontoxic but antigenic form is a toxoid.
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