Cells use enzymes internally to grow, reproduce and create energy, and they often excrete enzymes outside their cell walls as well. For example, E. coli bacteria excrete enzymes to help break down food molecules so they can pass through the cell wall into the cell.
Peptidases break peptides down into individual amino acids.
Some proteases are extremely specialized, while others break down just about any chain of amino acids. Amylases - Amylases break down starch chains into smaller sugar molecules. Your saliva contains amylase and so does your small intestine. Lipases - Lipases break down fats . Cellulases - Cellulases break cellulose molecules down into simpler sugars.