Summary: Procedure used to measure the activity of Aspartate Amino Transferase (AST). AST activity is measured by the enzymatically coupled reactions of AST (to form oxaloacetate from aspartate and α-ketoglutarate) and malate dehydrogenase (conversion of oxaloacetate to malate with oxdiation of NADH to NAD). The rate of NAD formation is monitored by the change in absorbance at 340 nm.