An aminopeptidase A (EC was purified from subsp. NCDO 712. Of the 18 aminoacyl-alanine dipeptides tested, the enzyme hydrolysed Asp-Ala, Glu-Ala and Ser-Ala. It was also active against tripeptide substrates but did not hydrolyse Ala-Asp or Ala-Glu. The kinetics of dipeptide hydrolysis were allosteric with positive cooperativity of substrate binding. The Hill constants were 1.52 for Asp-Ala, 1.51 for Glu-Ala and 1.61 for Ser-Ala. The was found to be 245000 by gel-filtration chromatography. A single band corresponding to an of 41 000 was detected by SDS-PAGE of the purified enzyme which indicated that the enzyme is hexameric. Activity against glutamate -nitroanilide was optimum at 65 °C and pH 8. Activity was inhibited by 1 mM-EDTA, implying that the enzyme is metal-containing. Cu, Mn and Zn (all at 1 mM) inhibited activity and Co was stimulatory.


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