Ultrafiltration
The active fractions from Mono Q-Sepharose were combined
and applied to a stirred ultrafiltration cell (Millipore 8400; Millipore,
Billerica, MA) using a 10-kDa MW cut-off membrane (PBGC
membrane, Millipore). The concentrated enzyme was stored at
20 C for further analyses. All the purification steps were conducted
at temperatures not exceeding 4 C.