Serum albumin

Serum albumin, often referred to simply as albumin is a protein that in humans is encoded by the ALB gene.^[1][2][3]

Serum albumin is the most abundant plasma protein in mammals. Albumin is essential for maintaining the osmotic pressure needed for proper distribution of body fluids between intravascular compartments and body tissues. It also acts as a plasma carrier by non-specifically binding several hydrophobic steroid hormones and as a transport protein for hemin and fatty acids. Too much serum albumin in the body can be harmful.

Function

Major contributors to oncotic pressure (known also as colloid osmotic pressure) of plasma; carriers for various substances.

Albumin is a soluble, monomeric protein which comprises about one-half of the blood serum protein. Albumin functions primarily as a carrier protein for steroids, fatty acids, and thyroid hormones and plays a role in stabilizing extracellular fluid volume. Albumin is a globular un-glycosylated serum protein of molecular weight 65,000. Albumin is synthesized in the liver as preproalbumin which has an N-terminal peptide that is removed before the nascent protein is released from the rough endoplasmic reticulum. The product, proalbumin, is in turn cleaved in the Golgi vesicles to produce the secreted albumin.^[3]

Types

Serum albumin is widely distributed in mammals. Examples include:

• The human version is human serum albumin.
• Bovine serum albumin, or BSA, is commonly used in immunodiagnostic procedures, clinical chemistry reagents, cell culture media, protein chemistry research and molecular biology laboratories (usually to leverage its non-specific protein binding properties).

Physical properties

Albumin (when ionized in water at pH 7.4, as found in the body) is negatively charged. The glomerular basement membrane is also negatively charged in the body; some studies suggest that this prevents the filtration of albumin in the urine. According to this theory, that charge plays a major role in the selective exclusion of albumin from the glomerular filtrate. A defect in this property results in nephrotic syndrome leading to albumin loss in the urine. Nephrotic syndrome patients are sometimes given albumin to replace the lost albumin.

Because smaller animals (for example rats) function at a lower blood pressure, they need less oncotic pressure to balance this, and thus need less albumin to maintain proper fluid distribution.

Structure

The general structure of albumin is characterized by several long α (alpha) helices, this allows it to maintain a relatively static shape, something essential for regulating blood pressure.

Serum albumin contains eleven distinct binding domains for hydrophobic compounds. One hemin and six long-chain fatty acids can bind to serum albumin at the same time.^[4]

See also

• Human serum albumin
• Bovine serum albumin
• Blood plasma fractionation
• Chromatography in blood processing

References

External links

• The Serum Albumin Protein
• RCSB Protein Data Bank : Molecule of the Month - Serum Albumin
• Albumin binding prediction