1. An enzyme that is excreted externally and that acts outside the organism. 2. An enzyme that is attached to the external surface of the plasma membrane of a cell.
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ec·to·en·zyme .ek-tō-'en-.zīm n an enzyme acting outside the cell
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ec·to·en·zyme (ek″to-enґzīm) exoenzyme.Medical dictionary. 2011.