Alpha-1-Microglobulin (a1M)

Alpha-1-microglobulin (A1M), also known as protein HC (for Heterogeneous Charge), is a low molecular weight protein component of plasma first discovered in pathological human urine. It is a member of the lipocalin superfamily. Although much is now known of its structure and properties, the function and physiological role of A1M remains unclear, although evidence suggests that it functions in the regulation of the immune system. A1M is known to exist in both a free form and complexed to other macromolecules: immunoglobulin A (IgA) in humans and alpha-1-inhibitor-3 in the rat. Free A1M is a monomeric protein composed of one 188 residue polypeptide and contains three cysteines, two of which (residues 75 and 173) form a conserved intra-molecular disulphide link.