Identification and partial purification of a cation-sensitive neutral endopeptidase from bovine pituitaries

An apparently new endopeptidase with a pH optimum between 7.0 and 7.5 was purified 600 fold from bovine pituitaries. The enzyme hydrolyzed synthetic substrates such as Cbz-Gly-Gly-Leu-pNA and Cbz-Gly-Gly-Tyr-Leu-pNA by splitting the bond between the leucine residue and p-nitroaniline. Replacement of the leucine residue by alanine, greatly diminished the rate of reaction. Simple model trypsin and chymotrypsin substrates such as Bz-DL-Arg-2NA and N-succinyl-Phe-2NA were not attacked. The enzyme was also inactive toward aminopeptidase and carboxypeptidase substrates. Strong inhibition of the enzyme was observed at relatively low concentrations of sodium and potassium ions. Leupeptin, pepstatin and phenylmethylsulfonylfluoride had no effect on enzyme activity, however inhibition was obtained with p-mercuribenzoate. Preliminary experiments with filtration through Sephadex G-100 columns suggest a molecular weight in excess of 100,000.