And the four major mechanisms of action that we spoke of previously include Covalent catalysis acidbased catalysis, metal ion catalysis and catalysis by proximity and orientation. And so, to demonstrate these mechanisms, we're going to begin our discussion on the first group of protein enzymes used inside our body, namely the proteases. So what exactly is a protease? Well, a protease is a protein enzyme. It's an enzyme molecule that is a protein that catalyzes the hydrolysis, the breaking of peptide bonds and peptide bonds, also known as amide bonds are the bonds that hold amino acids together in any protein molecule, in any polypeptide chain. Now, why would we need to actually break a peptide bond in the first place?