PURIFICATION AND CHARACTERIZATION OF AN AMINOPEPTIDASE (PEP C-LIKE) FROM LACTOBACILLUS-CASEI SUBSP CASEI IFPL-731 ISOLATED FROM RAW GOATS MILK CHEESE

A Pep C-like aminopeptidase was purified from the cell-free extract of Lactobacillus casei subsp. casei IFPL 731 by ammonium sulphate precip itation, hydrophobic interaction chromatography, anion-exchange chroma tography, chromatofocusing and gel filtration. SDS-polyacrylamide gel electrophoresis showed one protein band of 50 kDa. The enzyme was a 20 0 kDa tetramer under non-reducing conditions. Activity was optimal at pH 7.5 and 55 degrees C and was inhibited by the thiol-group inhibitor , p-hydroxymercuribenzoate. Enzyme activity was strongly inhibited by 0.1 mM CU2+. The aminopeptidase hydrolyzed a wide range of p-nitroanil ide derivatives and several dipeptides and tripeptides, showing a pref erence for substrates containing hydrophobic residues at the N-termina l position. The enzyme showed a high affinity for Leu-pNA (K-m, 0.05 m M). (C) 1998 Elsevier Science Ltd. All rights reserved.