AFP, also known as alpha-fetoprotein, is a major plasma protein produced by the yolk sac and the liver during fetal development. It is thought to be the fetal form of serum albumin. This protein binds to copper, nickel, fatty acids and bilirubin. The main function of this is to prevent the virilization of female fetuses. As it does not bind estrogen, its function in humans is less clear. Recombinant human AFP, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.