Any of various enzymes found in cells that break down proteins, especially important in digestion and cellular breakdown processes.
From Greek kathaíresis (digestion) plus the enzyme suffix -in, coined in the 19th century when biochemists discovered these protein-breaking molecules. The Greek root connects to the idea of breaking down or dissolving.
Your cells are filled with cathepsins—tiny molecular scissors that break down old proteins—and when cells die, cathepsins actually digest the cell itself from the inside out.
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