An enzyme that is secreted or located on the outside surface of a cell, where it breaks down molecules in the cell's environment.
From Greek 'ekto-' (outside) + 'enzyme' (biological catalyst, from 'en-' within + 'zyme' fermentation). This biochemistry term emerged in the 20th century as scientists discovered enzymes functioning outside cells in digestive and immune processes.
Your saliva works because of ectoenzymes—these external enzymes start breaking down food the moment it enters your mouth, which is why chewing bread long enough makes it taste sweet.
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