Preparative separation of immunoglobulins from bovine colostrum by continuous divergent‐flow electrophoresis

Immunoglobulins in bovine colostrum were separated and fractionated from other proteins using the method and instrumentation developed in our laboratory. The proposed separation was based on bidirectional isotachophoresis/moving boundary electrophoresis with electrofocusing of the analytes in a pH gradient from 3.9 to 10.1. The preparative instrumentation included the trapezoidal non-woven fabric that served as separation space with divergent continuous flow. The defatted and casein precipitate-free colostrum supernatant was loaded directly into the instrument without any additional colostrum pre-preparation. Immunoglobulin G was fractionated from other immune proteins such as bovine serum albumin, β-lactoglobulin, and α-lactalbumin, and was continuously collected in separated fractions over 3 h. The fractions were further processed, and isolated immunoglobulin G in the liquid fractions was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by re-focusing in gel isoelectric focusing. Separated immunoglobulin G was detected in seven fractions by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a gradually decreased concentration in the fractions. Re-focusing of the proteins in the fractions by gel isoelectric focusing revealed multiple separated zones of immunoglobulin G with the isoelectric point values covering the range from 5.4 to 7.2. Each fraction contained distinct zones with gradually increased isoelectric point values and decreased concentrations from fraction to fraction.