Aspartate transaminase (AST) is similar to alanine transaminase (ALT) in that it is another enzyme associated with liver parenchymal cells.It is raised in acute liver damage. It is also present in red blood cells and cardiac muscle, skeletal muscle, and kidney and brain tissue, and may be elevated due to damage to those sources as well.AST was defined as a biochemical marker for the diagnosis of acute myocardial infarction in 1954. However the use of AST for such a diagnosis is now redundant and has been superseded by the cardiac troponins.

The 2 isoenzymes are homodimeric. In liver about 80% of the enzyme activity is mitochondrial in origin, whereas in serum the enzyme activity is largely cytosolic.