Serum albumin
Encyclopedia
Serum albumin, often referred to simply as albumin is a protein
that in humans is encoded by the ALB gene
.
Serum albumin is the most abundant plasma protein in mammal
s. 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 acid
s. Too much serum albumin in the body can be harmful.
(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 steroid
s, fatty acid
s, and thyroid hormone
s 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 vesicle
s to produce the secreted albumin.
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 rat
s) function at a lower blood pressure
, they need less oncotic pressure
to balance this, and thus need less albumin to maintain proper fluid distribution.
Serum albumin contains eleven distinct binding domains for hydrophobic compounds. One hemin
and six long-chain fatty acid
s can bind to serum albumin at the same time.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the ALB gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
Serum albumin is the most abundant plasma protein in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. Albumin is essential for maintaining the osmotic pressure
Osmotic pressure
Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane....
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
Hemin
Hemin is an iron-containing porphyrin. More specifically, it is Protoporphyrin IX containing a ferric iron ion with a chloride ligand....
and fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s. Too much serum albumin in the body can be harmful.
Function
Major contributors to oncotic pressureOncotic pressure
Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins in blood plasma that usually tends to pull water into the circulatory system.Throughout the body, dissolved compounds have an osmotic 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 steroid
Steroid
A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...
s, fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s, and thyroid hormone
Thyroid hormone
The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland primarily responsible for regulation of metabolism. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine ,...
s and plays a role in stabilizing extracellular fluid volume. Albumin is a globular un-glycosylated
Glycosylation
Glycosylation is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule . In biology glycosylation refers to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules...
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
Endoplasmic reticulum
The endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...
. The product, proalbumin, is in turn cleaved in the Golgi vesicle
Golgi apparatus
The Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
s to produce the secreted albumin.
Types
Serum albumin is widely distributed in mammals. Examples include:- The human version is human serum albuminHuman serum albuminHuman serum albumin is the most abundant protein in human blood plasma. It is produced in the liver. Albumin constitutes about half of the blood serum protein...
. - Bovine serum albuminBovine serum albuminBovine serum albumin is a serum albumin protein derived from cows. It is often used as a protein concentration standard....
, or BSA, is commonly used in immunodiagnostic procedures, clinical chemistry reagents, cell culture media, protein chemistry research and molecular biologyMolecular biologyMolecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
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 membraneGlomerular basement membrane
The glomerular basement membrane is the basal laminal portion of the glomerulus. The Glomerular capillary endothelial cells, the GBM and the filtration slits between the podocytes perform the filtration function of the glomerulus, separating the blood in the capillaries from the filtrate that...
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
Nephrotic syndrome
Nephrotic syndrome is a nonspecific disorder in which the kidneys are damaged, causing them to leak large amounts of protein from the blood into the urine....
leading to albumin loss in the urine. Nephrotic syndrome patients are sometimes given albumin to replace the lost albumin.
Because smaller animals (for example rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s) function at a lower blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
, they need less oncotic pressure
Oncotic pressure
Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins in blood plasma that usually tends to pull water into the circulatory system.Throughout the body, dissolved compounds have an osmotic 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
Hemin
Hemin is an iron-containing porphyrin. More specifically, it is Protoporphyrin IX containing a ferric iron ion with a chloride ligand....
and six long-chain fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s can bind to serum albumin at the same time.
See also
- Human serum albuminHuman serum albuminHuman serum albumin is the most abundant protein in human blood plasma. It is produced in the liver. Albumin constitutes about half of the blood serum protein...
- Bovine serum albuminBovine serum albuminBovine serum albumin is a serum albumin protein derived from cows. It is often used as a protein concentration standard....
- Blood plasma fractionationBlood plasma fractionationBlood plasma fractionation refers to the general processes of separating the various components of blood plasma, which in turn is a component of blood obtained through blood fractionation.-Blood plasma:...
- Chromatography in blood processingChromatography in blood processingChromatographic techniques have been used in blood processing and purification since the 1980s. It has emerged as an effective method of purifying blood components for therapeutic use.-Human blood plasma:...