Purification of lentil lectins using preparative electrophoresis

Electrophoresis presents an interesting alternative to chromatography for the purification of biological compounds. To document the performance of three preparative electrophoresis apparatus currently available, they were applied to the purification of lectins from lentil seeds which contain two isolectins usually purified by chromatography. Purification by electrophoresis consists of first isolating a mixture of the two isolectins and then separating them. For the first step, either of two free-flow electrophoresis apparatus were employed: the Elphor VaP 22, using field step electrophoresis and the Biostream using zone electrophoresis. To optimize the process, the Biostream was modified to a recycling mode. This required repositioning one dialysis membrane which separates an electrode from the separation chamber. This allowed the lentil extract to be desalted by electrodialysis directly in the apparatus prior to fractionation. A high concentration of lectins was collected at the cathode and acidic proteins were collected at the anode. The bulk of the extract was recycled until the whole volume was processed. In a second step the isolectins were separated by recycling isoelectric focusing in the recycling isoelectric focusing apparatus. The present work clearly demonstrates that electrophoretic methods provide lectins with higher purity than chromatographically purified commercial products.