A protein is a biological macromolecule that consists of amino acids with peptide bonds between them. Proteins are found in all cells and usually account for more than 50 percent of their dry weight. They not only provide structure but also have essential functions as “molecular machines”. They enable cell movements, transport metabolites, pump ions, catalyze chemical reactions and can detect signaling substances. The molecular mass of proteins ranges from 10,000 to 1,000,000 per molecule. Enzymatic hydrolysis of proteins by peptidases is called proteolysis. Auto-proteolysis is when a peptidase degrades itself. Proteolysis can be inhibited by protease inhibitors.