Purification and partial characterization of an intracellular aminopeptidase from Streptococcus salivarius subsp. thermophilus strain ACA-DC 114

E. TSAKALIDOU AND G. KALANTZOPOULOS. 1992. An intracellular aminopeptidase from Streptococcus salivarius subsp. thermophilus strain ACA-DC 114, isolated from traditional Greek yoghurt, was purified by chromatography on DEAE-cellulose and Sephadex G-100. The enzyme had a molecular weight of 89 000. It was active over a pH range 4.5-9.5 and had optimum activity on L-lysyl-4-nitroanilide at pH 6.5 and 35°C with K _m= 1.80 mmol/l; above 55°C the enzyme activity declined rapidly. The aminopeptidase was capable of degrading substrates by hydrolysis of the N -terminal amino acid; it had very low endopeptidase and no carboxypeptidase activity. The enzyme was strongly inactivated by EDTA. Serine and sulphydryl group reagents had no effect on enzyme activity.