My thesis is about the preference of cyclooxygenase 2 over prostacyclin synthase. I mutated the C terminus of cyclooxygenase 2 and then analysed the production of prostaglandins. My research revealed that the C terminus removal results in a lower production of prostacyclin. It can thus be concluded that the C terminus plays a significant role in the preference of cyclooxygenase 2 over prostacylin synthase.