Preparation of bacterial X-prolyl dipeptidyl aminopeptidase and its stabilization by organic cosolvents.

To obtain large amounts of the X-prolyl dipeptidyl aminopeptidase from Lactococcus lactis subsp lactis (PepX, E.C. 3.4.14.5), PepX was purified from a commercial L. lactis cell extract. The enzyme was purified in only three steps and the last one was performed by HPLC on a C4 reverse-phase column using acetonitrile as an eluent. Despite its high molecular mass (175 kDa), the enzyme was recovered with a good activity yield (75%). Advantages and drawbacks of this technique compared to the classical ones are discussed. The stability of the enzyme in aqueous solutions and in the presence of 10 water-miscible solvents was also investigated. PepX was found to be stabilized by dimethyl sulfoxide, triglyme, and glycerol.