The transaminase enzyme was first discovered by Braunstein and Kritzman in 1938 in pigeon breast muscle. This enzyme was later purified by Cohnen in 1940. In 1941, Cohnen showed that the enzyme transaminase was particularly abundant in cardiac and skeletal muscle. it was this observation that lead La Due and his associates to estimate serum levels of transaminase following myocardial infarction with the idea that the necrotic myocardium would be likely to liberate aminopherase into the blood stream. They also discovered that hepatitis and skeletal muscle necrosis were responsible for elevated serum levels of the enzyme.