Identification and Partial Purification of a Dipeptidyl Aminopeptidase from Streptococcus faecalis

A dipeptidyl aminopeptidase was identified in Streptococcus faecalis JH2SS and was partially purified (approximately 245-fold) by HPLC. Gel filtration chromatography indicated an M r of 140 000. The partially purified enzyme exhibited a requirement for Co2+. The pH optimum for the hydrolysis of l-Val-l-Ala-p-nitroanilide was approximately 9·5. The apparent K m for this substrate was 0·22 mm. The enzyme preferentially hydrolysed X-Ala-Y substrates, but also utilized X-Pro-Y substrates, and therefore is most closely related to the mammalian dipeptidyl aminopeptidase II (EC 3.4.14.-). The enzyme was inhibited by p-chloromercuribenzoate, but not by iodoacetate, N-ethylmaleimide or the serine protease inhibitor phenylmethylsulphonyl fluoride.