Use of a preparative-scale, recirculating isoelectric trapping device for the isolation and enrichment of acidic proteins in bovine serum

A recirculating, preparative-scale isoelectric trapping device, developed for the binary isoelectric trapping separation of proteins has been used to desalt, isolate and enrich the pI < 4 protein fraction from a 150 mL sample of bovine serum. Subsequent re-separation of the 2 < pI < 4 fraction with pH 3.0, 3.5 and 3.9 buffering membranes resulted in distinct, narrow pI fractions whose components could be readily analyzed by reversed-phase HPLC, even though they were below the detection limit in the original bovine serum sample. The entire isoelectric trapping process (from desalting to collection of the final, narrow pI fractions) took only 7 h, indicating the potential of the recirculating, preparative-scale isoelectric trapping device as a front-end component in the proteomic work-flow when sufficiently large samples are available.