Purification and Properties of a Periplasmic Aminoendopeptidase from Escherichia coli

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Abstract
A periplasmic aminoendopeptidase from Escherichia coli has been purified to homogeneity. It is a monomer of molecular weight 45000 and containing one – SH group that is necessary for catalytic activity. The study of its substrate specificity indicated that the enzyme has both aminopeptidase and endopeptidase activity. The pH optimum for l-alanine p-nitroanilide hydrolysis is between 7 and 7.5 and that for 125I-labelled casein proteolysis between 7.3 and 7.6. The activation energy for the hydrolysis of l-alanine p-nitroanilide was calculated to be 5.3 kcal × mol−1 (22.2 kJ × mol−1).