Orosomucoid (alpha1-acid glycoprotein)

General Information

Alpha1-acid glycoprotein (also known as orosomucoid) is a classical acute phase protein showing a 3-4 fold increase during inflammation or tissue damage. Concentrations of this protein peak 3-5 days after the initiating event. Decreased levels are associated with severe liver disease and protein losing syndromes. Structurally it belongs to the lipocalin superfamily of secretory proteins. The lipocalin protein superfamily is one of exhibits diversity at the level of sequence and function. It consists of more than 25 small extracellular proteins originating from a wide variety of tissues in vertebrate and invertebrate animals, plants and bacteria. Lipocalins are characterised by three molecular recognition properties: the binding of small hydrophobic substances, the binding to cell-surface receptors, and the formation of complexes with other soluble macromolecules. A typical lipocalin consists of a 160-180 amino-acid peptide, folded into 8-9 b-strands which form a coffee filter-like cone with a hydrophobic interior. The plasma proteins: retinol-binding protein, alpha1-acid glycoprotein , and alpha-1 microglobulin, the nasal odorant-binding proteins, the bilin-binding proteins of butterflies and crustacyanin, the protein which gives the shell of crayfish its unusual colour properties, are all examples of lipocalins.

Alpha1-acid glycoprotein promotes fibroblast growth and interacts with collagen. Its main clinical use is in the assessment of acute and recurring inflammations as well as of tumours with cell necrosis. It can be used to differentiate bewteen acute phase reactions (where it is elevated) and oestrogen induced effects (concentrations normal or decreased). Along with haptoglobin, it is a useful marker of slight in vivo haemolysis.