Aminopeptidase A(Pep A)is a metal-dependent enzyme that specifically hydrolyze peptides with the N-terminal amino acids glutamic acid(Glu)and aspartic acid(Asp).A possible application of PepA is the hydrolysis of Glu/Asp-rich food proteins such as wheat gluten and casein,increasing the flavor and solubility of food protein.In the present study,the gene encoding a Pep A from Lactococcus lactis ssp.lactis IL1403 was synthesized and introduced into Pichia pastoris GS115(His4).Lc-Pep A was successfully expressed and secreted to the culture medium,followed by identification and purification to homogeneity.Characteristics study demonstrated that Lc-Pep A could specifically hydrolyze the substrates Glu-pNA and Asp-pNA with similar catalytic activity,and this was further confirmed by the kinetics parameters measured.Additionally,Lc-Pep A showed a broad thermostability and pH stability with an optimum temperature of 60℃and an optimum pH of 8.0.The enzyme activity of Lc-Pep A was activated by metal ions Co2+,Mn2+,and Zn2+ but was strongly inhibited by Ni2+and Cu2+.The routine proteinase inhibitor had no effect on the activity of Lc-Pep A.However,Lc-Pep A was strongly inhibited by the metallopeptidase inhibitor,EDTA,and disulfide bond-reducing agents.The study may facilitate production and application of Lc-Pep A.
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