Molecular model of cyclooxygenase-1 enzyme (COX-1, blue and grey spirals) complexed with eicosapentaenoic acid (EPA, blue ball-and-stick model). EPA is a polyunsaturated omega-3 fatty acid, present in fish oil. COX-1 is the enzyme that catalyses the reaction that converts EPA into prostaglandins: lipids used in the body for tissue repair and mediating inflammation. Amino acid Tyr 385 is needed for this catalysis to occur and the other labelled amino acids shown are needed for the correct positioning of the substrate, EPA. COX-1 also has a protoporphyrin IX ring (upper left, grey spheres) with cobalt (blue) in the centre.