Characterization of an aminopeptidase from Pseudozyma hubeiensis 31-B and potential applications

Yeast strain 31-B was isolated from the digestive juices of Nepenthes alata as an aminopeptidase producer and identified as Pseudozyma hubeiensis via morphological testing and comparative 26S ribosomal DNA-D1/D2 gene sequence analysis. Strain 31-B produced aminopeptidase as extracellular peptidase, but proteinase activity was not detected in the culture filtrate. The aminopeptidase from strain 31-B was purified from filtered culture medium by (NH4)2SO4 precipitation and four column chromatography steps: Diethylaminoethyl (DEAE)-Toyopearl 650 M, Butyl-Toyopearl 650 M, hydroxylapatite, and Toyopearl HW-55. Sodium dodecyl sulfate polyacrylamide gel electrophoresis yielded the purified enzyme as a single band with molecular mass 75.3 kDa. The optimum temperature and pH were approximately 40 °C and 8.0, respectively. The purified aminopeptidase preferentially hydrolyzed Leu-p-NA and its activity was inhibited by ethylenediaminetetraacetic acid. The isolated aminopeptidase reduced the bitterness of peptides generated from milk casein using a bacterial proteinase. These results show that the aminopeptidase produced by P. hubeiensis 31-B has potential application as a food additive in the dairy industry.