As its name suggests, alpha-2-macroglobulin is a large protein. It is synthesized in the liver. Its main function is to inhibit the activity of certain enzymes to ensure correct blood clotting. Alpha-2-macroglobulin is also an acute-phase protein. Levels tend to increase somewhat in an entire series of inflammatory attacks and to be low in cases of severe liver damage.
The interest for alpha-2-macroglobulin in electrophoresis is due to its large size. It is so big that it is held in the blood even in the most severe of kidney conditions. A high percentage of alpha-2-macrobglobulin (but not the level in grams per litre) therefore indicates that proteins of smaller sizes were lost by a damaged kidney (nephrotic syndrome).