We've been using the S219V mutant for cleaving out tags. We usually do our cleavage reactions in an overnight dialysis after a Ni-column into 50mM Tris, 100-200 mM NaCl, 5 mM BME at 4C. I've never found problems with losing any protein in the reaction and recover usually >90% of the protein after passing through the column a second time to remove the tag and protease.
Feel free to contact me if you have any questions. Best of luck, Peter
