Aspartic aminotransferase has two isoenzymes, namely, the cytoplasmic aspartic aminotransferase (s-ast) and the mitochondrial aspartic aminotransferase (m-ast), which are widely found in liver, heart, skeletal muscle, kidney and other tissues of animals or humans, especially the heart and liver.In general, the activity of s-ast in serum is much higher than that of m-ast, and the activity of m-ast accounts for less than 10% of the total AST activity. However, when there is liver damage, especially when there is necrosis of heart and liver cells, the activity of m-ast is significantly increased.

                                                     m-AST   

L-Aspartic acid+α-Ketodioic acid一→Oxaloacetate+glutamic acid.

                                                   MDH

Oxaloacetate+α-Ketoglutarate一→L-Malic acid+NAD﹢.