globulin

globulin

globulin, any of a large family of proteins of a spherical or globular shape that are widely distributed throughout the plant and animal kingdoms. Many of them have been prepared in pure crystalline form. The term globulin is a partly procedural one, used in classifying an otherwise diverse group of proteins that are soluble in water or dilute salt solutions. Among the most important are the immunoglobulins (Ig), the antibodies of the immune system (see immunity). They are classified into five types based upon structure: IgA, IgD, IgE, IgG, and IgM. IgG or γ-globulin is the most common and forms about 70% of the immunoglobins in the blood. Other globulins are involved in the transport of a variety of substances, including lipids, hormones, and inorganic ions.

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Globulin

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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

globulin

[′gläb·yə·lən]

(biochemistry)

A heat-labile serum protein precipitated by 50% saturated ammonium sulfate and soluble in dilute salt solutions.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

globulin

any of a group of simple proteins, including gamma globulin, that are generally insoluble in water but soluble in salt solutions and coagulated by heat

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005