globulin

[GLOBUL(E) + -IN.]

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A general name for any member of a heterogeneous group of serum proteins precipitated by 50% saturated ammonium sulfate. See also Protein; Serum.

The introduction of electrophoresis during the 1930s permitted subdivision of the globulins into alpha, beta, and gamma globulins on the basis of relative mobility at alkaline pH (8.6). However, each of these subgroups, though electrophoretically homogeneous, consists of a great variety of proteins with different biological properties and markedly different sizes and chemical properties other than net charge. Thus the α₂-globulins, for example, as defined by moving boundary or paper electrophoresis, contain proteins ranging in molecular weight from approximately 50,000 to approximately 1,000,000 (α₂-macroglobulin), each with differing functions. See also Electrophoresis; Immunoglobulin.

Globular (as opposed to fibrous) proteins that are relatively insoluble in water, but soluble in dilute salt solutions. They occur in blood (serum globulins, including immunoglobulins), milk (lactoglobulins), and some plants.

A class of proteins.

A general term for proteins that are insoluble in water or highly concentrated salt solutions but soluble in moderately concentrated salt solutions. All plasma proteins except albumin and prealbumin are globulins. The plasma globulins can be separated into five fractions by serum protein electrophoresis (SPE). In order of decreasing electrophoretic mobility these fractions are the alpha₁, alpha₂, beta₁ and beta₂ globulins, and the gamma globulins.
The globulins include carrier proteins, which transport specific substances; acute phase reactants, which are involved in the inflammatory process; clotting factors; complement components; and immunoglobulins. Examples are transferrin, a beta₁ globulin that transports iron, and alpha₁-antitrypsin, an acute phase reactant that inhibits serum proteases. The gamma globulin fraction is almost entirely composed of immunoglobulins.

• accelerator g. — a substance present in plasma, but not in serum, that functions in the formation of intrinsic and extrinsic thromboplastin; called also clotting factor V.
• antihemophilic g. (AHG) — clotting factor VIII.
• antilymphocyte g. (ALG) — a substance used as an immunosuppressive agent in organ transplantation, usually in combination with immunosuppressive drugs; it is the gamma globulin fraction of antilymphocyte serum.
• immune g. — a sterile solution containing antibodies normally present in blood, derived from donor animals, sometimes after hyperimmunization with certain microorganisms; used for passive immunization against some infectious diseases and in the treatment of gamma globulin deficiency.
• serum g. — the fraction of proteins precipitated from blood serum by half saturation with ammonium sulfate; the principal groups include the α-, β- and γ-globulins.

Globulin is one of the two types of serum proteins, the other being albumin. This generic term encompasses a heterogeneous series of families of proteins, with larger molecules and less soluble in pure water than albumin, which migrate less than albumin during serum electrophoresis. The normal range in blood is 2 to 3.5 g/dl.

It is sometimes used synonymously with globular protein. However, albumin is also a globular protein, but not a globulin. All other serum globular proteins are globulins.

Protein electrophoresis is used to categorize globulins into the following four categories:

• Alpha 1 globulins
• Alpha 2 globulins
• Beta globulins
• Gamma globulins (one group of gamma globulins are immunoglobulins, that function as antibodies)

Reference ranges for blood tests, comparing blood content of globulins (shown in purple at right) with other constituents.

External links

• Serum Proteins
• Cornell
• Understanding and interpreting serum protein electrophoresis
• MeSH Globulins

v • d • e Proteins Processes Protein biosynthesis - Posttranslational modification - Protein folding - Protein targeting - Proteome - Protein methods Structures Protein structure - Protein structural domains - Proteasome Types List of types of proteins - List of proteins - Membrane protein - Globular protein (Globulin, Albumin) - Fibrous protein

v • d • e Proteins: globulins Serum Alpha globulins serpins: alpha-1 (Alpha 1-antichymotrypsin, Alpha 1-antitrypsin) · alpha-2 (Alpha 2-antiplasmin) · Antithrombin (Heparin cofactor II) carrier proteins: alpha-1 (Transcortin) · alpha-2 (Ceruloplasmin) · Retinol binding protein other: alpha-1 (Orosomucoid) · alpha-2 (alpha-2-Macroglobulin, Haptoglobin) Beta globulins carrier proteins: Sex hormone-binding globulin · Transferrin other: Angiostatin · Haemopexin · Beta-2 microglobulin · Factor H · Plasminogen · Properdin Gamma globulin Immunoglobulins Other Fibronectin · Macroglobulin/Microglobulin · Transcobalamin Other Beta-lactoglobulin (Lactoferrin) · Thyroglobulin · Alpha-lactalbumin

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The original article states: “Globulin is one of the two types of serum proteins, the other being albumin.” However, according to Marieb & Hoehn (2007, pg. 649, Table 17.1), there are in fact, three types of serum proteins, including the aforementioned globulin, albumin, as well as fibrinogen. Reference: Marieb, E. M., & Hoehn, K. (2007). Human Anatomy & Physiology (7th ed.). San Francisco, CA: Pearson Benjamin Cummings.

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