Globulin

Not to be confused with globin or globular protein.

The globulins are a family of globular proteins that have higher molecular weights than albumins and are insoluble in pure water but soluble in dilute salt solutions. Some globulins are produced in the liver, while others are made by the immune system. Globulins, albumin, and fibrinogen are the major blood proteins. The normal concentration of globulins in human blood is about 2.6-4.6 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 four categories:

• Alpha 1 globulins
• Alpha 2 globulins
• Beta globulins
• Gamma globulins (one group of gamma globulins are the immunoglobulins, which are also known as "antibodies")

Globulins can be distinguished from one another using serum protein electrophoresis.

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

Sizes

Globulins exist in various sizes. The lightest globulins are the alpha globulins, which typically have molecular weights of around 92 kDa, while the heaviest class of globulins are the gamma globulins, which typically weigh about 120 kDa. Being the heaviest, the gamma globulins are among the slowest to segregate in gél electrophoresis. Since they are immunologically active, they are also called "immunoglobulins".

Nonhuman globulins

Crystal structure of a pumpkin seed globulin

Globulin proteins exist not only in other animal species, but also in plants. Vicilin and legumin, from peas and other legumes, function as protein storage within seeds. These proteins can cause allergic reactions if they bind with human IgE antibodies.

Pseudoglobulins and euglobulins

Pseudoglobulins are a class of globulins that are more soluble in ammonium sulfate than euglobulins. Pseudoglobulins are also soluble in pure water, while euglobulins are not.

External links

• Cornell
• Globulins at the US National Library of Medicine Medical Subject Headings (MeSH)