Purification and characterization of an aminopeptidase from Lactobacillus delbrueckii subsp. bulgaricus

Abstract An aminopeptidase was purified from cell-free extracts of Lactobacillus delbrueckii subsp. bulgaricus B14. Electrophoretic purity was achieved by anion exchange chromatography, metal chelating chromatography with immobilized Cu 2+ , and two steps of FPLC anion exchange chromatography. A molecular mass of 95 kDa was calculated by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme probably does not consist of subunits. Suitable substrates for activity assays were l -Lys-NA and l -Ala- l -Arg-NA which were cleaved fastest at 50°C and pH 7. The peptidase is a metal-dependent enzyme which was inhibited completely by 0·1 m m EDTA. Activity was increased by 1 m m Mn 2+ and 0·1 m m Hg 2+ . Aminopeptidase activity inhibited by EDTA could be restored by the addition of Mn 2+ . Properties of the enzyme are compared to the corresponding enzymes of other species of lactic acid bacteria.