Albumin

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Not to be confused with serum albumin.
This article is about the class of proteins. For the substance sometimes called albumen, see Egg white. For other uses, see Albumin (disambiguation).
Serum albumin family
PDB 1ao6 EBI.jpg
Structure serum albumin.[1][2]
Identifiers
Symbol Serum_albumin
Pfam PF00273
Pfam clan CL0282
InterPro IPR014760
SMART SM00103
PROSITE PS51438
SCOP 1ao6
SUPERFAMILY 1ao6

The albumins (formed from Latin: albumen[3] "(egg) white; dried egg white") are a family of globular proteins, the most common of which is serum albumin. The albumin family consists of all proteins that are water-soluble, are moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins are commonly found in blood plasma, and are unique from other blood proteins in that they are not glycosylated. Substances containing albumins, such as egg white, are called albuminoids.

A number of blood transport proteins are evolutionarily related, including serum albumin, alpha-fetoprotein, vitamin D-binding protein and afamin.[4][5][6]

Function[edit]

Serum albumin is the main protein of human blood plasma.[7] 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 colloidal osmotic 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 biological role of afamin (alpha-albumin) has not yet been characterised.[citation needed]

Structure[edit]

The 3D structure of human serum albumin has been determined by X-ray crystallography to a resolution of 2.5 Å.[8] Albumin is a 65-70 kDa protein.

Albumin comprises three homologous domains that assemble to form a heart-shaped molecule.[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, as shown schematically below:

                    +---+          +----+                        +-----+
                    |   |          |    |                        |     |
 xxCxxxxxxxxxxxxxxxxCCxxCxxxxCxxxxxCCxxxCxxxxxxxxxCxxxxxxxxxxxxxxCCxxxxCxxxx
   |                 |       |      |             |               |
   +-----------------+       +------+             +---------------+
 
C = cysteine, x = any amino acid

Types[edit]

Serum albumin[edit]

Main article: Serum albumin

Serum albumin is the most abundant blood plasma protein and is produced in the liver and forms a large proportion of all plasma protein. The human version is human serum albumin, and it normally constitutes about 50% of human plasma protein.[7]

Serum albumins are important in regulating blood volume by maintaining the oncotic pressure (also known as colloid osmotic pressure) of the blood compartment.[7] They also serve as carriers for molecules of low water solubility this way isolating their hydrophobic nature, including lipid soluble hormones, bile salts, unconjugated bilirubin, free fatty acids (apoprotein), calcium, ions (transferrin), and some drugs like warfarin, phenobutazone, clofibrate & phenytoin. For this reason, it's sometimes referred as a molecular "taxi". Competition between drugs for albumin binding sites may cause drug interaction by increasing the free fraction of one of the drugs, thereby affecting potency.

Specific types include:

Low albumin (hypoalbuminemia) may be caused by liver disease, nephrotic syndrome, burns, protein-losing enteropathy, malabsorption, malnutrition, late pregnancy, artefact, genetic variations and malignancy.

High albumin (hyperalbuminemia) is almost always caused by dehydration. In some cases of retinol (Vitamin A) deficiency, the albumin level can be elevated to high-normal values (e.g., 4.9 g/dL). This is because retinol causes cells to swell with water (this is also the reason too much Vitamin A is toxic).[9] In lab experiments it has been shown that All-trans retinoic acid down regulates human albumin production[10]

Normal range of human serum albumin in adults (> 3 y.o.) is 3.5 to 5 g/dL. For children less than three years of age, the normal range is broader, 2.9-5.5 g/dL.[11]

Albumin binds to the cell surface receptor Albondin.

Other types[edit]

Other types include the storage protein ovalbumin in egg white, and different storage albumins in the seeds of some plants, including hemp.[12]

  • Note that the protein 'albumin' is spelled with an "i", while "albumen" with an "e", is the white of an egg, which contains (among other things) several dozen types of albumin (with an 'i'), mostly ovalbumin.

Medical uses[edit]

For patients with low blood volume, there is no evidence that albumin reduces mortality when compared with cheaper alternatives such as normal saline, or that albumin reduces mortality in patients with burns and low albumin levels. Therefore, the Cochrane Collaboration recommends that it not be used, except in clinical trials.[13]

In acoustic droplet vaporization (ADV), albumin is sometimes used as a surfactant. ADV has been proposed as a cancer treatment by means of occlusion therapy.[14]

See also[edit]

References[edit]

  1. ^ Sugio S, Kashima A, Mochizuki S, Noda M, Kobayashi K; Kashima; Mochizuki; Noda; Kobayashi (June 1999). "Crystal structure of human serum albumin at 2.5 A resolution". Protein Eng. 12 (6): 439–46. doi:10.1093/protein/12.6.439. PMID 10388840. 
  2. ^ a b c He XM, Carter DC; Carter (1992). "Atomic structure and chemistry of human serum albumin". Nature 358 (6383): 209–15. doi:10.1038/358209a0. PMID 1630489. 
  3. ^ Historia Naturalis 28, 6, 18.  |first1= missing |last1= in Authors list (help)
  4. ^ Haefliger DN, Moskaitis JE, Schoenberg DR, Wahli W; Moskaitis; Schoenberg; Wahli (October 1989). "Amphibian albumins as members of the albumin, alpha-fetoprotein, vitamin D-binding protein multigene family". J. Mol. Evol. 29 (4): 344–54. doi:10.1007/BF02103621. PMID 2481749. 
  5. ^ Schoentgen F, Metz-Boutigue MH, Jollès J, Constans J, Jollès P; Metz-Boutigue; Jollès; Constans; Jollès (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". Biochim. Biophys. Acta 871 (2): 189–98. doi:10.1016/0167-4838(86)90173-1. PMID 2423133. 
  6. ^ Lichenstein HS, Lyons DE, Wurfel MM, Johnson DA, McGinley MD, Leidli JC, Trollinger DB, Mayer JP, Wright SD, Zukowski MM; Lyons; Wurfel; Johnson; McGinley; Leidli; Trollinger; Mayer; Wright; Zukowski (July 1994). "Afamin is a new member of the albumin, alpha-fetoprotein, and vitamin D-binding protein gene family". J. Biol. Chem. 269 (27): 18149–54. PMID 7517938. 
  7. ^ a b c Farrugia A (January 2010). "Albumin usage in clinical medicine: tradition or therapeutic?". Transfus Med Rev 24 (1): 53–63. doi:10.1016/j.tmrv.2009.09.005. PMID 19962575. 
  8. ^ Sugio S , Kashima A , Mochizuki S , Noda M , Kobayashi K; Kashima; Mochizuki; Noda; Kobayashi (June 1999). "Crystal structure of human serum albumin at 2.5 A resolution". Protein Engineering 12 (6): 439–446. doi:10.1093/protein/12.6.439. PMID 10388840. 
  9. ^ Gaull, H; Wright, CE; Gaull, GE (December 1984). "Protective effect of taurine, zinc and tocopherol on retinol-induced damage in human lymphoblastoid cells.". J Nutr. 114 (12): 2256–61. PMID 6502269. 
  10. ^ Suzuki, T; Matsuura, T; Ohkawa, K; Miyamura, T; Okazaki, I; Watanabe, T; Suzuki, T (July 2006). "All-trans retinoic acid down-regulates human albumin gene expression through the induction of C/EBPbeta-LIP". Biochem J. 397 (2): 345–53. doi:10.1042/BJ20051863. PMC 1513275. PMID 16608438. 
  11. ^ "Normal Ranges for Common Laboratory Tests." Rush University
  12. ^ "Hemp Repairs Damaged DNA". High Times. 28 Aug 2014. Retrieved 10 Sep 2014. 
  13. ^ Albumin Reviewers (Alderson p, Bunn F (2011). "Human albumin solution for resuscitation and volume expansion in critically ill patients". Cochrane Database Syst Rev (10): CD001208. doi:10.1002/14651858.CD001208.pub3. PMID 21975732. 
  14. ^ Lo, A. H.; Kripfgans, O. D.; Carson, P. L.; Rothman, E. D.; Fowlkes, J. B. (May 2007). "Acoustic droplet vaporization threshold: effects of pulse duration and contrast agent". IEEE Trans Ultrason Ferroelectr Freq Control 54 (5): 933–946. doi:10.1109/tuffc.2007.339. PMID 17523558. 

External links[edit]

This article incorporates text from the public domain Pfam and InterPro IPR014760