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.
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".
Non human globulins
Globulin proteins exist in other species as well, such as in dogs and plants: cucurbitin from squashes and vicilin and legumin from legumes and peas, functioning as protein storage within seeds. These proteins can cause allergic reactions if they bind with human IgE antibodies.
Pseudoglobulins and euglobulins
- Sanchez-Monge, R.; Lopez-Torrejón, G.; Pascual, C. Y.; Varela, J.; Martin-Esteban, M.; Salcedo, G. (12 November 2004). "Vicilin and convicilin are potential major allergens from pea". Clinical & Experimental Allergy 34 (11): 1747–1753. doi:10.1111/j.1365-2222.2004.02085.x.
- Harris, T; Eagle (1935). "THE IMMUNOLOGICAL SPECIFICITY OF THE EUGLOBULIN AND PSEUDOGLOBULIN FRACTIONS OF HORSE AND HUMAN SERUM". J Gen Physiol 19 (2): 383–396. doi:10.1085/jgp.19.2.383. PMC 2141424. PMID 19872935.
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