Albumin is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

globular protein In biochemistry, globular proteins or spheroproteins are spherical ("globe-like") proteins and are one of the common protein types (the others being fibrous, disordered and membrane proteins). Globular proteins are somewhat water-soluble (form ...

s, the most common of which are the

serum albumin Serum albumin, often referred to simply as blood albumin, is an albumin (a type of globular protein) found in vertebrate blood. Human serum albumin is encoded by the ''ALB'' gene. Other mammalian forms, such as bovine serum albumin, are chem ...

s. All of the proteins of the albumin family are water-

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins are commonly found in

blood plasma Blood plasma is a light Amber (color), amber-colored liquid component of blood in which blood cells are absent, but which contains Blood protein, proteins and other constituents of whole blood in Suspension (chemistry), suspension. It makes up ...

and differ from other

blood proteins Plasma proteins, sometimes referred to as blood proteins, are proteins present in blood plasma. They perform many different functions, including transport of hormones, vitamins and minerals in activity and functioning of the immune system. Other ...

in that they are not

glycosylated Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not ...

. Substances containing albumins are called ''albuminoids''. A number of blood transport proteins are evolutionarily related in the albumin family, including serum albumin,

alpha-fetoprotein Alpha-fetoprotein (AFP, α-fetoprotein; also sometimes called alpha-1-fetoprotein, alpha-fetoglobulin, or alpha fetal protein) is a protein that in humans is encoded by the ''AFP'' gene. The ''AFP'' gene is located on the ''q'' arm of chromosome ...

vitamin D-binding protein Vitamin D-binding protein (DBP), also/originally known as gc-globulin (group-specific component), is a protein that in humans is encoded by the ''GC'' gene. DBP is genetically the oldest member of the albuminoid family and appeared early in the ev ...

and

afamin Afamin is a protein that in humans is encoded by the ''AFM'' gene. Function This gene is a member of the albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All of the proteins of the album ...

. This family is only found in

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

. ''Albumins'' in a less strict sense can mean other proteins that coagulate under certain conditions. See ' for

lactalbumin Lactalbumin, also known as "whey protein", is the albumin contained in milk and obtained from whey. Lactalbumin is found in the milk of many mammals. There are alpha Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet ...

ovalbumin Ovalbumin (abbreviated OVA) is the main protein found in egg white, making up approximately 55% of the total protein. Ovalbumin displays sequence and three-dimensional homology to the serpin superfamily, but unlike most serpins it is not a serine ...

and plant "2S albumin".

Function

Albumins in general are transport proteins that bind to various

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s and carry them around. Human types include: *

Human serum albumin Human serum albumin is the serum albumin found in human blood. It is the most abundant protein in human blood plasma; it constitutes about half of serum protein. It is produced in the liver. It is soluble in water, and it is monomeric. 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 acid In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...

s, hormones,

bilirubin Bilirubin (BR) (adopted from German, originally bili—bile—plus ruber—red—from Latin) is a red-orange compound that occurs in the normcomponent of the straw-yellow color in urine. Another breakdown product, stercobilin, causes the brown ...

, thyroxine (T4) and pharmaceuticals (including barbiturates). Its main function is to regulate the

oncotic pressure Oncotic pressure, or colloid osmotic-pressure, is a type of osmotic pressure induced by the plasma proteins, notably albumin, in a blood vessel's plasma (or any other body fluid such as blood and lymph) that causes a pull on fluid back into ...

of blood. The

isoelectric point The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electric charge, electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). Howe ...

of albumin is 4.7. *

Alpha-fetoprotein Alpha-fetoprotein (AFP, α-fetoprotein; also sometimes called alpha-1-fetoprotein, alpha-fetoglobulin, or alpha fetal protein) is a protein that in humans is encoded by the ''AFP'' gene. The ''AFP'' gene is located on the ''q'' arm of chromosome ...

is a fetal plasma protein that binds various cations, fatty acids and bilirubin. *

Vitamin D-binding protein Vitamin D-binding protein (DBP), also/originally known as gc-globulin (group-specific component), is a protein that in humans is encoded by the ''GC'' gene. DBP is genetically the oldest member of the albuminoid family and appeared early in the ev ...

binds to vitamin D and its metabolites, as well as to fatty acids. * Not much is known about

. It seems to carry lipidated Wnt proteins and Vitamin E around. * Extracellular matrix protein 1 is a less canonical albumin. It regulates bone mineralization. The four canonical human albumins are arranged on chromosome 4 region 4q13.3 in a tandem manner.

Classification

Albumins found in animals can be divided into six subfamilies by

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

. 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. In addition to their medical use, serum albumins are valued in biotechnology.

Bovine serum albumin Bovine serum albumin (BSA or "Fraction V") is a serum albumin protein derived from cows. It is often used as a protein concentration standard in lab experiments. The nickname "Fraction V" refers to albumin being the fifth fraction of the origin ...

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: *

Ovalbumin Ovalbumin (abbreviated OVA) is the main protein found in egg white, making up approximately 55% of the total protein. Ovalbumin displays sequence and three-dimensional homology to the serpin superfamily, but unlike most serpins it is not a serine ...

is a storage protein in egg white (albumen). It is a

serpin Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be ...

. *

Lactalbumin Lactalbumin, also known as "whey protein", is the albumin contained in milk and obtained from whey. Lactalbumin is found in the milk of many mammals. There are alpha Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet ...

, or

whey protein Whey protein is a mixture of proteins isolated from whey, the liquid material created as a by-product of cheese production. The proteins consist of α-lactalbumin, β-lactoglobulin, serum albumin and immunoglobulins. Glycomacropeptide also m ...

, is a protein fraction of milk. It is mainly Beta-lactoglobulin, although serum albumin also comprises a small part of it. * Some plant

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

s, including

hemp Hemp, or industrial hemp, is a plant in the botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial and consumable use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest ...

, encode " 2S albumins". These are named for their egg-like coagulation property.

Structure

The 3D structure of human serum albumin has been determined by X-ray crystallography to a resolution of . Albumin is a 65–70 kDa protein. Albumin comprises three homologous domains that assemble to form a heart-shaped protein. Each domain is a product of two subdomains that possess common structural motifs. 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 detection

Worldwide, certain

traditional Chinese medicine Traditional Chinese medicine (TCM) is an alternative medicine, alternative medical practice drawn from traditional medicine in China. A large share of its claims are pseudoscientific, with the majority of treatments having no robust evidence ...

s contain wild bear bile, banned under

CITES CITES (shorter acronym for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of inte ...

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.

Etymology

Albumin is pronounced ; formed from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

: ''

albumen Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens, it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms aro ...

'' "egg white", itself derived from the latin ''albus'': white.

References

External links

*
The Albumin website

Albumin binding prediction

PDBe-KB
provides an overview of all the structure information available in the PDB for Human Serum albumin. {{Authority control Blood proteins A