An aminopeptidase with a very broad substrate specificity was purified to homogeneity from SBT 2171 by FPLC. The enzyme was purified 144-fold from a cell-free extract with a yield of 16%. The purified enzyme appeared as a single band on an SDS-PAGE gel. It had a molecular mass of 95 kDa and an isoelectric point of 4.9. The enzyme hydrolysed a large range of naphthylamide- and nitroanilide-substituted amino acids, as well as several di-, tri- and oligopeptides. It also exhibited significant prolineiminopeptidase-like activity, since it hydrolysed several proline-containing peptides. Prolyl--nitroanilide was hydrolysed with a low affinity (Michaelis-Menten constant 0.6 mM) and a of 2.5 μmol min (mg protein) while lysyl--nitroanilide was hydrolysed with a high affinity 0.003 mM; 37.5 μmol min (mg protein)]. The aminopeptidase activity, which was optimal between pH 6.0 and 8.0 and at 50 °, was very stable at 30 ° for more than 7 d. The activity lost by treatment with the thiol-blocking reagents could be restored with ß-mercaptoethanol, while Co and Mn restored the activity of the EDTA-treated enzyme. Immunological experiments with antibodies raised against the aminopeptidases from and clearly showed that both aminopeptidases are at least immunologically different from each other.


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