This article is about the class of proteins. For the substance sometimes called albumen, see egg white. For the specific albumins found in vertebrate bloodstreams, see serum albumin. For other uses, see Albumin (disambiguation).
Albumin is a family of globular proteins, the most common of which are the serum albumins. All of the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins are commonly found in blood plasma and differ from other blood proteins in that they are not glycosylated. Substances containing albumins are called albuminoids.
Albumins in general are transport proteins that bind to various ligands and carry them around.[6] Human types include:
Human serum albumin is the main protein of human blood plasma. It makes up around 50% of human plasma proteins. It binds water, cations (such as Ca2+, Na+ and K+), fatty acids, hormones, bilirubin, thyroxine (T4) and pharmaceuticals (including barbiturates). Its main function is to regulate the oncotic pressure of blood.[7] The isoelectric point of albumin is 4.7.[8]
Alpha-fetoprotein is a fetal plasma protein that binds various cations, fatty acids and bilirubin.
The four canonical human albumins are arranged on chromosome 4 region 4q13.3 in a tandem manner.[10]
Classification
Albumins found in animals can be divided into six subfamilies by phylogeny. The Vitamin-D binding proteins occupy families 1–3. The other albumins are mixed among each other in families 4–6. ECM1 is in family 6.[6]
In addition to their medical use, serum albumins are valued in biotechnology. Bovine serum albumin is usually used, although versions from humans and genetically-modified rice are also used to reduce animal cruelty.
Other albumin types
A few other proteins are also sometimes called albumins. They are not in the same family as vertebrate albumins:
Some plant seeds, including hemp, encode "2S albumins". These are named for their egg-like coagulation property.[11]
Structure
The 3D structure of human serum albumin has been determined by X-ray crystallography to a resolution of
2.5 ångströms (250 pm).[1] Albumin is a 65–70 kDa protein.
Albumin comprises three homologous domains that assemble to form a heart-shaped protein.[2] Each domain is a product of two subdomains that possess common structural motifs.[2] The principal regions of ligand binding to human serum albumin are located in hydrophobic cavities in subdomains IIA and IIIA, which exhibit similar chemistry. Structurally, the serum albumins are similar, each domain containing five or six internal disulfide bonds.
Forensic uses
Worldwide, certain traditional Chinese medicines contain wild bear bile, banned under CITES legislation. Dip sticks, similar to common pregnancy tests, have been developed to detect the presence of bear albumin in traditional medicine products, indicating that bear bile had been used in their creation.[12]
Terminology
Albumin is pronounced /ˈælbjʊmɪn/; formed from Latin: albumen[13] "(egg) white; dried egg white".
See also
Cohn process (human serum albumin purification method)
^ abSugio S, Kashima A, Mochizuki S, Noda M, Kobayashi K (June 1999). "Crystal structure of human serum albumin at 2.5 A resolution". Protein Engineering. 12 (6): 439–46. doi:10.1093/protein/12.6.439. PMID10388840.
^Haefliger DN, Moskaitis JE, Schoenberg DR, Wahli W (October 1989). "Amphibian albumins as members of the albumin, alpha-fetoprotein, vitamin D-binding protein multigene family". Journal of Molecular Evolution. 29 (4): 344–54. Bibcode:1989JMolE..29..344H. doi:10.1007/BF02103621. PMID2481749. S2CID1456034.
^Schoentgen F, Metz-Boutigue MH, Jollès J, Constans J, Jollès P (June 1986). "Complete amino acid sequence of human vitamin D-binding protein (group-specific component): evidence of a three-fold internal homology as in serum albumin and alpha-fetoprotein". Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 871 (2): 189–98. doi:10.1016/0167-4838(86)90173-1. PMID2423133.
^Farrugia A (January 2010). "Albumin usage in clinical medicine: tradition or therapeutic?". Transfusion Medicine Reviews. 24 (1): 53–63. doi:10.1016/j.tmrv.2009.09.005. PMID19962575.
^Nishio H, Heiskanen M, Palotie A, Bélanger L, Dugaiczyk A (May 1996). "Tandem arrangement of the human serum albumin multigene family in the sub-centromeric region of 4q: evolution and chromosomal direction of transcription". Journal of Molecular Biology. 259 (1): 113–9. doi:10.1006/jmbi.1996.0306. PMID8648639.
