Endoprotease

Part of speech: noun

Definitions

1. An enzyme that breaks peptide bonds inside the interior of a protein chain rather than at its ends
2. A protein-digesting enzyme that cuts a polypeptide at internal sites, splitting it into smaller fragments
3. A class of proteolytic enzymes acting on bonds away from the termini of amino acid chains within proteins

Etymology: Endoprotease is a compound built from two parts, and the first is a Greek prefix that describes where the action happens. "Endo-" comes from the Greek "endon," meaning "within" or "inside," and it appears in scientific coinages such as "endoscope" and "endothermic." A protease is an enzyme that breaks down proteins by cutting the chains of amino acids that make them up, and the word combines "protein" with the Greek-derived suffix "-ase," used for enzymes generally. Put together, an endoprotease is a protease that cuts a protein chain at points inside the chain rather than chewing away at its ends. The contrast is with exopeptidases, which trim amino acids one at a time from the terminal positions. The distinction is a practical one for biochemists, who use it to describe how an enzyme attacks its target.