The globulins are a family of

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 (formi ...

s that have higher

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

s than albumins and are insoluble in pure water but dissolve in dilute salt solutions. Some globulins are produced in the liver, while others are made by the immune system. Globulins, albumins, and

fibrinogen Fibrinogen (factor I) is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood clo ...

are the major

blood protein Blood-proteins, also termed plasma proteins, are proteins present in blood plasma. They serve many different functions, including transport of lipids, hormones, vitamins and minerals in activity and functioning of the immune system. Other blood pr ...

s. The normal concentration of globulins in human blood is about 2.6-3.5 g/dL. The term "globulin" is sometimes used synonymously with "globular protein". However, albumins are also globular proteins, but are ''not'' globulins. All other serum globular proteins are globulins.

Types of globulins

All globulins fall into one of the following three categories : *

Alpha globulins Alpha globulins are a group of globular proteins in plasma that are highly mobile in alkaline or electrically charged solutions. They inhibit certain blood proteases and show significant inhibitor activity. The alpha globulins typically have mo ...

Beta globulins Beta globulins are a group of globular proteins in plasma that are more mobile in alkaline or electrically charged solutions than gamma globulins, but less mobile than alpha globulins. Examples of beta globulins include: * beta-2 microglobulin ...

Gamma globulins Gamma globulins are a class of globulins, identified by their position after serum protein electrophoresis. The most significant gamma globulins are immunoglobulins (antibodies), although some immunoglobulins are not gamma globulins, and some g ...

(one group of gamma globulins is the

immunoglobulin An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

s, which are also known as "antibodies") Globulins can be distinguished from one another using

serum protein electrophoresis Serum protein electrophoresis (SPEP or SPE) is a laboratory test that examines specific Blood proteins, proteins in the blood called globulins. The most common indications for a serum protein electrophoresis test are to diagnose or monitor multip ...

. Globulins exert

oncotic pressure Oncotic pressure, or colloid osmotic-pressure, is a form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel's plasma (blood/liquid) that causes a pull on fluid back into the capillary. Participating colloids displace ...

. Their deficiency results in loss of carrier functions of globulins, oedema due to decreased oncotic pressure, and susceptibility to infections due to decreased gamma-globulins (immuno-globulins) leading to decreased production of antibodies.

Sizes ~ weights

Globulins exist in various sizes. The lightest globulins are the alpha globulins, which typically have molecular weights of around 93

kDa The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at re ...

, while the heaviest class of globulins are the gamma globulins, which typically weigh about 1193 kDa. Being the heaviest, the gamma globulins are among the slowest to segregate in gel electrophoresis. The immunologically active gamma globulins are also called "

s" or "

antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

Human blood plasma levels

The normal concentration of globulins in human blood is about 2.6-4.6 g/dL. Blood values sorted by mass and molar concentration

Nonhuman globulins

Crystal structure of pumpkin seed globulin

Globulin proteins exist not only in other animal species, but also in plants.

Vicilin Vicilin is a legumin-associated globulin protein. Vicilin can be described as a storage protein found in legumes such as the pea or lentil. Vicilin is a protein that protects plants from fungi and microorganism. It has been hypothesized it's an all ...

and

legumin Legumin is family of globular proteins obtained from beans, peas, lentils, vetches, hemp (specifically edestin) and other leguminous seeds. Edestin is a biologically active legumin protein that is digestible for human bodies. Garden peas are a co ...

, from peas and other legumes, function as protein storage within seeds. These proteins can cause allergic reactions if they bind with human

IgE Immunoglobulin E (IgE) is a type of antibody (or immunoglobulin (Ig) " isotype") that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains (ε chain) and two light chains, with the ε c ...

antibodies.

Pseudoglobulins and euglobulins

Pseudoglobulins are a class of globulins that are more soluble in

ammonium sulfate Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...

than euglobulins. Pseudoglobulins are also soluble in pure

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

, while euglobulins are not.

References

External links

* Blood proteins {{protein-stub