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

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Abstract
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 Km= 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.