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A new serine carboxypeptidase gene,  capA , was identified in  Aspergillus niger  CBS 513.88 by reading genomic information and performing sequence alignment, and the gene was cloned and expressed in  Pichia pastoris  GS115. In a shake flask, the enzyme activity of the recombinant strain GS115 (pPIC9K- capA ) reached 209.3 U mg −1 . The optimal temperature and pH for enzyme activity were determined to be 45 °C and 6.0, respectively. After incubation at 40–50 °C or at pH 4.0–8.0 for 1 h, the enzyme retained more than 80% or 60% of its initial activity. The presence of 1–10 mmol L −1  Mg 2+  enhanced the activity of CapA, whereas 1–10 mmol L −1  Cu 2+ , Fe 2+ , or Co 2+ , 10 mmol L −1  Mn 2+ , or 1–10 mmol L −1  phenylmethylsulfonyl fluoride (PMSF) significantly inhibited its activity. CapA had a broad substrate specificity and preferred the hydrophobic amino acids Leu and Lys at the C terminus of proteins, and  N -benzyloxycarbonyl- l -phenylalanyl- l -leucine (Cbz-Phe-Leu) was the optimal substrate, for which CapA exhibited  K  m  0.063 mmol L −1  and  k  cat  /K  m  186.35 mmol L −1  s −1 . The good thermostability, pH stability and hydrolysis characteristics of CapA provide a solid foundation for application in the food and biotechnology fields.

A new carboxypeptidase from Aspergillus niger with good thermostability, pH stability and broad substrate specificity