Trypsin. Polarized light micrograph of crystals of the digestive enzyme trypsin. Trypsin is involved in the digestion of proteins by breaking down peptones into smaller peptide chains. Peptones are large protein fragments produced by enzyme action in the first stages of protein digestion. Trypsin is secreted by the pancreas in an inactive form, trypsinogen, which is converted to trypsin in the duodenum by the action of the enzyme enteropeptidase. Magnification: x100 at 6x7cm size.