α₁-Acid Glycoprotein (AAG, Orosomucoid)

Abstract

α₁-Acid glycoprotein is found in human serum and in the serum of many other species. Although the biological function of this protein is unknown it is well established that it has a relatively high affinity for steroids — especially progesterone; it also binds certain drugs. Scatchard analysis shows that there is one primary binding site for progesterone and other Δ⁴-3-ketosteroids per mol of protein. The interaction of steroids with AAG¹ is mainly hydrophobic in nature and, accordingly, follows the polarity rule. The transport of progesterone in human serum is primarily mediated by CBG and by albumin; the contribution of AAG to the total binding capacity is very small.