globulin

Globulins are a group of water-soluble, globular proteins found in blood serum and other bodily fluids. They are distinct from albumin and are commonly categorized by electrophoretic mobility into alpha, beta, and gamma fractions. In humans, the gamma globulin fraction contains immunoglobulins (antibodies) produced by plasma cells, while the alpha and beta fractions include a variety of transport and enzymatic proteins.

Within the human serum, alpha globulins include proteins such as alpha-1 antitrypsin and several carrier proteins; beta globulins include transferrin, which transports iron, and various components of the complement system and lipoprotein-related proteins. The gamma globulins are largely composed of immunoglobulins (IgG, IgA, IgM, IgD, and IgE), which mediate humoral immunity by recognizing and neutralizing pathogens.

Globulins are largely synthesized in the liver, with many alpha and beta globulins produced there, and immunoglobulins synthesized by plasma cells in lymphoid tissues. They perform diverse roles, including transport of metal ions and lipids, regulation of proteolysis, immune defense, and participation in the coagulation and inflammatory cascades.

Clinical relevance is often assessed through serum protein electrophoresis, which separates the globulin fractions. Abnormal globulin patterns can indicate infections, autoimmune diseases, liver disorders, or gammopathies such as multiple myeloma, where a monoclonal gamma globulin spike may be observed. Globulin levels may also decrease in immunodeficiency or protein-losing conditions.

In plants, globulins also refer to a class of seed storage proteins, such as vicilins and legumins, which are distinct from serum globulins in animals.