Albumin
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Albumin (Latin: albus, white) refers generally to any protein with water solubility, which is moderately soluble in concentrated salt solutions, and experiences heat coagulation (protein denaturation). Substances containing albumin, such as egg white, are called albuminoids. It has a molecular weight of about 65kD (65,000 Atomic mass units) and consists of 584 amino acids and contains no carbohydrate.
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[edit] Types
[edit] Serum albumin
The most well-known type of albumin is serum albumin. It is most common in the blood or serum (providing its name) but it can also appear in other fluid compartments (providing the basis for the CSF/serum albumin ratio, for example.)
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 60% of human plasma protein.
Serum albumins are important in regulating blood volume by maintaining the oncotic pressure (also known as colloid osmotic pressure) of the blood compartment. 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:
- human serum albumin
- bovine serum albumin (cattle serum albumin) or BSA, often used in medical and molecular biology labs.
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 become raised to High-normal values (ex: 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).[1] In lab experiments it has been shown that All-trans retinoic acid down regulates human albumin production[2]
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, 2.5-5.5 g/dL.[3]
Albumin binds to the cell surface receptor Albondin.
[edit] Other types
Other types include the storage protein ovalbumin in egg white, and different storage albumins in the seeds of some plants.
- 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.
[edit] Albumin Measurement
Plasma albumin is a component of the Liver Function Tests (LFTs) but may be ordered separately. Albumin can be measured in Serum (yellow-top tube), plain tube with no additives (red-top tube) or heparin plasma (green-top tube). The reference interval is 36 - 52 g/L. (note upper limit increased from 47 g/L on the 15th June 2007) One of the method used is Bromocresol green on a Roche Modular or Olympus AU2700 analyser.
[edit] References
- ^ Gaull (December 1984). "Protective effect of taurine, zinc and tocopherol on retinol-induced damage in human lymphoblastoid cells.". J Nutr.. PMID 6502269.
- ^ Suzuki (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. PMID 16608438.
- ^ "Normal Ranges for Common Laboratory Tests." Rush University. [1]
[edit] External links
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Wikisource has the text of the 1911 Encyclopædia Britannica article Albumin. |
[edit] See also
- Cohn process (human serum albumin purification method)
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