Among the plasma proteins, the physician understands the proteins of the blood plasma, which are also called blood protein. From the blood serum, the plasma differs by its coagulation factors, which also belong to the plasma proteins. Overall, the blood plasma contains approximately one hundred different proteins and glycoproteins. On 100 milliliters of blood plasma, the proteins account for about six to eight grams. The term "serum protein" should be distinguished from plasma proteins.
Serum proteins are all blood proteins minus the coagulation factor fibrinogen. By electrophoresis, the plasma proteins can be split into albumins and globulins. This means that the proteins of the blood plasma as charged colloidal parts or molecules in the migration through an electric field in albumin and globulins share. These two groups are present in plasma in an approximate ratio of 40 to 60 percent.
Globulins are either α1, α2, γ or β globulins. The electrophoretic mobility of these four subgroups is their most important distinguishing feature. In addition to about four percent α1-globulins, the plasma contains about eight percent α2-globulins and twelve percent β-globulins. The γ-globulins make up the largest proportion of blood plasma with 16 percent. The biosynthesis of plasma proteins occurs mainly in the liver and in the lymph.
Glycoproteins undergo translation via posttranslational modification. Glycosyl residues bind in their active form to nucleoside diphosphate. Glycosyl transferases bind to proteins. Like all proteins, plasma proteins are biological macromolecules of amino acids. Globular proteins are almost spherical in the quartic or tertiary structure. More than 100 amino acids are linked in chains to proteins. The proteins of the blood plasma are also called spheroplasts. They are easy to dissolve in water and saline.
Plasma proteins take on versatile tasks in the human body. On the one hand, they maintain the colloid osmotic pressure, which in turn plays a role in the maintenance of plasma volume. Also, the pH of the blood is maintained by plasma proteins. Apart from that, the blood protein has a transport function. They transport water-insoluble substances through the body and are therefore also called carrier proteins.
Also, the transport of hormones and enzymes takes place on carrier proteins of blood plasma. For blood clotting, especially plasma proteins such as fibrinogen, which help with homeostasis, are irreplaceable. In addition, plasma proteins take over important tasks in processes of the immune system, such as in inflammation. In this context, immunoglobulins or antibodies are also mentioned, which are formed in response to antigens. Immunoglobulins recognize foreign bodies and bind to these antigens to destroy them. Among the α1-globulins is mainly transcortin, which is responsible for the transport of steroids. The α1-antitrypsin inhibits protease. The same applies to α1-antichymotrypsin. The plasma protein HDL is a carrier protein for blood lipids.
Prothrombin acts as a proenzyme of thrombin and transcobalamin transports cobalamin through the bloodstream. The α2-globulins include haptoglobin, which binds and transports hemoglobin. α2-macroglobulin and α2-antithrombin inhibit blood clotting while caeruloplasmin transports copper. The β-globulins include transferrin, which is responsible for the transport of iron. β-lipoprotein transports blood lipids, while fibrinogen is known as a blood coagulation factor. Hemopexin is a last β-globulin and binds to free heme. The immunoglobulins belong to the fifth globulin group, whose components are also known as γ-globulins.
In dysproteinemias, shifts occur in the quantitative ratio of blood proteins. This phenomenon can be either innate or acquired. Acquired dysproteinemias can be caused for example by acute infections. The proportion of albumins in this case decreases and the proportion of globulins increases. This phenomenon can also occur with greater blood loss or after surgery. To distinguish these acquired forms of dysproteinemia is a congenital maldistribution, as it is the case of alpha-1-antitrypsin deficiency.
Due to a genetic defect, too little alpha-1-antitrypsin is produced. There is also a question of defective proteinemia in the case of a genetically determined lack of individual plasma proteins. This should be distinguished from paraproteinaemia. In the context of this disease, certain immunoglobulins or chains of immunoglobulins are increasingly formed. Such processes occur, for example, in the context of Waldenström's disease. This is a malignant lymphoma disease, the lymphoma cells operate an overproduction of immunoglobulin M. Multiple myeloma also has an excess concentration of immunoglobulins. In this cancer of the bone marrow, the antibody-producing cells proliferate in the blood plasma.
These degenerate plasma cells produce an excess of antibodies or antibody fragments. In addition, both hypoproteinaemia and hyperproteinemia may occur in the context of plasma proteins. At the former appearance, the concentration of plasma proteins falls below 66 grams per liter. In hyperproteinemia, however, the concentration is above 83 grams per liter. The cause of hypoproteinemia may be, for example, liver damage or malnutrition. Hyperproteinemias, on the other hand, are usually associated with inflammatory processes and can occur, for example, in the context of tuberculosis.