Characterization of the Aminopeptidase System fromLactobacillus caseiSubsp.caseiIFPL 731

The cell-free extract of Lactobacillus casei subsp. casei IFPL 731 was subjected to ammonium sulfate precipitation, hydrophobic interaction chromatography, two steps of anion-exchange chromatography, and gel filtration. Six peaks with aminopeptidase (Ap) activity toward p -nitroanilide ( p NA) derivatives were found (Ap I to Ap VI). Ap I, Ap III, Ap IV, and Ap V hydrolyzed preferentially Lys- p NA and were identified as metalloenzymes; only Ap IV was strongly activated by the sulfydryl group reagent p -hydroxymercuribenzoic acid. Peak Ap II cleaved Leu- p NA, but not Lys- p NA or Arg- p NA, and it was not affected by inhibitors of metallopeptidases but by p -hydroxymercuribenzoic acid. Ap VI preferentially hydrolyzed Leu- p NA, and it was a metalloenzyme. Ap III was purified to homogeneity and identified as an aminopeptidase N with a molecular mass of 95 kDa by SDS−PAGE as well by gel filtration. Ap IV was also purified and seems to be tetrameric with a molecular mass of 30 kDa.