Optimal conditions for protease use in the assay of serum mitochondrial aspartate aminotransferase

The optimal conditions for selective proteolytic inactivation of cytosolic aspartate aminotransferase (c‐AST) to determine mitochondrial aspartate aminotransferase (m‐AST) in serum were studied. Protease 401 was found to be effective over a pH range of 6.0‐10.0. A pH of 9.5 with 0.5% albumin in the reagent mixture was determined to be optimal for inactivation of c‐AST and preservation of m‐AST, lactic dehydrogenase (LDH), and malic dehydrogenase (MDH) in the assay procedure. The presence of serum endogenous protein inhibitors such as aα 1 ‐antitrypsin and α 2 ‐macroglobin did not inhibit protease 401.