Blood group typing by electrophoresis based on isoelectric focusing

The electrophoresis of proteins and enzymes is described with respect to its application and contribution to the blood group typing in the medico-legal field. Isoelectric focusing (IEF) has many advantages over conventional electrophoresis because of minimizing band diffusion, higher resolution, phenotyping under equilibrium and non-equilibrium conditions. The difference between the resolving capabilities of IEF and conventional electrophoresis is due to the pH environment within the gel. In IEF, protein separation is accomplished in a pH gradient across a gel and the net charge of a protein is variable, whereas with conventional electrophoresis the pH is essentially constant throughout the gel and net charge of a protein is also constant. A variable net charge difference along the gel plays an important role for good separation under non-equilibrium conditions. Moreover, the appropriate addition of chemical separators increases the net charge difference of proteins under non-equilibrium conditions and provides good resolution in shorter focusing times. The chemical separators also improve the resolution of isozymes and increase the protein solubility as a result of the buffering capacity. On the other hand, a shift of isozyme patterns from the same individual can be observed depending on the kind of sample. The shift is caused by the hemoglobin in phosphoglucomutase (PGM1) typing, the actin in group specific component (GC) typing and the different isoelectric points (pI) in α-1-antitrypsin (PI) typing. Therefore, the most suitable technique should be selected based on the system used and the sample conditions.