<P> A number of blood transport proteins are evolutionarily related, including serum albumin, alpha - fetoprotein, vitamin D - binding protein and afamin . </P> <P> Albumin binds to the cell surface receptor albondin . </P> <P> Serum albumin is the main protein of human blood plasma . It binds water, cations (such as Ca, Na and K), fatty acids, hormones, bilirubin, thyroxine (T4) and pharmaceuticals (including barbiturates): its main function is to regulate the Oncotic pressure of blood . Alpha - fetoprotein (alpha - fetoglobulin) is a fetal plasma protein that binds various cations, fatty acids and bilirubin . Vitamin D - binding protein binds to vitamin D and its metabolites, as well as to fatty acids . The isoelectric point of albumin is 4.9 . </P> <P> The 3D structure of human serum albumin has been determined by X-ray crystallography to a resolution of 2.5 ångströms (250 pm). Albumin is a 65--70 kDa protein . </P>

What is the function of albumin in blood