Fig. 3

Purification of VcIIIPK in BL21-AI strain (a, b) and preservation of the purified enzyme (c, d). a SDS-PAGE (12%) of a freshly purified VcIIIPK at different protein concentrations and b the same desalted sample of VcIIIPK after a month (old VcIIIPK) of being stored with 80% ammonium sulfate. Lane M indicates the low range molecular weights (Sigma Marker). c Residual activity and d SDS-PAGE (12%) of VcIIIPK after the first days of purification and storage in different conditions: A. without glycerol at 4 °C, B. 20% glycerol at 4 °C, C. 20% glycerol at − 20 °C and D. 20% glycerol at − 70 °C. 100% of activities without and with glycerol were 176 ± 29 and 185 ± 23 μmoles/min mg, respectively. In c the error bars represent the standard deviation of three independent experiments. d Performed from one of the experiments of c. Lane M shows the broad range molecular weights (BIO-RAD)