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.

Any of a major class of proteins insoluble in pure water and soluble in dilute saline (salt) solutions. In their natural state, the protein chain is folded into a globular form. Globulins are found in many plants, especially cereals. Globulins in animal fluids include enzymes, antibodies (the gamma globulins), lipoproteins, complement components, transport proteins, and various types of fibrous and contractile proteins.

Learn more about globulin with a free trial on Britannica.com.

Subgroup of the globulins. In humans and many other mammals, most antibodies are in the gamma globulin fraction of blood. A human gamma globulin preparation may be administered (by injection) to persons lacking immunity, either generally or to a particular disease, after exposure or before expected exposure.

Learn more about gamma globulin with a free trial on Britannica.com.

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.

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)

External links

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