Electrophoresis: It is the movement of charged molecules in an electrical field towards the oppositely charged electrode. It is used for separation of proteins for diagnosis of some diseases such as immune disease, genetic diseases (such as Hb S and Hb C diseases. The rate of migration of charged molecules depends on: a - amount of charge on the molecule OR b- molecular weight (size) of the molecule if the charge is equal. Serum protein electophoresis: In the standard method, serum samples are applied to support medium (agarose gel) on plate close to the cathode end. Both ends of support medium is immersed in alkaline buffer (pH 8.6), so proteins in this pH will be negatively charged.

2) The support strip is connected to two electrodes and a current is passed through the strip to separate proteins. 3) As serum proteins are negatively charged, they will move toward anode (positive electrode). Serum proteins move according to their density and amount of charge then arranged into 5 bands: albumin moves faster to the anode followed by α1 globulin, α2 globulin, β globulin and γ globulins.

 In case of decreased serum albumin (hypoalbuminaemia), the albumin band becomes less dense. This occurs,for example, in advanced liver disease as liver is the site of albumin synthesis. The separated proteins are made visible by staining. 4) Density (Intensity of color) of each band is directly proportional to its serum concentration, so albumin will show the most dense band (serum albumin is gm%, while globulins gm%).

Electrophoresis

Electrophoresis apparatus

Use of Protein Electrophoresis to diagnose sickle cell HbA moves faster than HbS because it is more negatively chareged (glutamic acid (negatively charged) in Hb A is replaced by valine (non polar in HbS). Carriers have both HbA and HbS so the sample will be separated as two bands (one for HbA, the faster) and the second for HbS.