Blood & Laboratory Values

Plasma Proteins – Function & Diseases

Plasma proteins

The proteins in the blood plasma are called plasma proteins . They differ from serum proteins primarily in their coagulation factors. The plasma proteins take on numerous tasks in the organism and can be affected by deficiency symptoms in the context of various diseases.

What are plasma proteins?

The physician understands the plasma proteins to be the proteins of the blood plasma, which are also referred to as blood proteins . Plasma differs from blood serum in its coagulation factors, which also belong to the plasma proteins. In total, about one hundred different proteins and glycoproteins are contained in the blood plasma. The proteins make up about six to eight grams per 100 milliliters of blood plasma. The term serum protein must be distinguished from plasma proteins.

Serum proteins are all blood proteins minus the clotting factor fibrinogen . The plasma proteins can be split into albumins and globulins by electrophoresis. This means that the proteins in the blood plasma, as charged colloidal parts or molecules, divide into albumins and globulins when migrating across an electric field. These two groups are present in plasma in an approximate ratio of 40 to 60 percent.

Anatomy & Structure

Globulins are either α1, α2, γ or β globulins. The electrophoretic mobility of these four subgroups is their main distinguishing feature. In addition to around four percent α1-globulins, the plasma contains around eight percent α2-globulins and twelve percent β-globulins. At 16 percent, γ-globulins make up the largest proportion of blood plasma. The biosynthesis of plasma proteins takes place mainly in the liver and in the lymph . 

In glycoproteins, translation occurs via post-translational modification. In their active form, glycosyl residues bind to nucleoside diphosphate. Glycosyl transferases bind them to proteins. Like all proteins, plasma proteins are biological macromolecules made up of amino acids . Globular proteins are nearly spherical in quaternary or tertiary structure. More than 100 amino acids are linked to form chains in proteins. The proteins in blood plasma are also known as spheroproteins. They are easily soluble in water and saline.

Function & Tasks

Plasma proteins perform a variety of tasks in the human body. On the one hand, they maintain colloid osmotic pressure, which in turn plays a role in maintaining plasma volume. The pH of the blood is also 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.

The transport of hormones and enzymes also takes place on carrier proteins in the blood plasma. Plasma proteins such as fibrinogen, which help with homeostasis, are particularly important for blood coagulation. In addition, plasma proteins take on important tasks in processes of the immune system , such as in inflammation . In this context, there is also talk of immunoglobulins or antibodies , which react to antigensare formed. Immunoglobulins recognize foreign bodies and bind to these antigens to destroy them. Transcortin, which is responsible for the transport of steroids, is one of the α1-globulins. 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 ceruloplasmin transports copper. Transferrin, which is responsible for the transport of iron , belongs to the β-globulins . β-lipoprotein transports blood lipids while fibrinogen is known as a blood clotting factor . Hemopexin is a final β-globulin and binds free heme. The immunoglobulins belong to the fifth globulin group, whose components are also known as γ-globulins.

Diseases

In the case of dysproteinemia, there are shifts in the quantitative ratio of blood proteins. This phenomenon can be either congenital or acquired. Acquired dysproteinemias can be caused, for example, by acute infections. In this case, the proportion of albumins decreases and the proportion of globulins increases. This phenomenon can also occur with major blood loss or after surgery. A distinction must be made between these acquired forms of dysproteinemia and congenital maldistribution, as is the case with alpha-1-antitrypsin deficiency. 

Due to a genetic defect, too little alpha-1-antitrypsin is produced. A genetic deficiency of individual plasma proteins is also referred to as defect proteinemia. Paraproteinemia is to be distinguished from this. As part of this disease, certain immunoglobulins or chains of immunoglobulins are increasingly formed. Such processes occur, for example, in the context of Waldenstrom’s disease . This is a malignant lymphoma disease in which the lymphoma cells overproduce immunoglobulin M. There is also an overconcentration of immunoglobulins in multiple myeloma. In this cancer of the bone marrow, the antibody-producing cells in the blood plasma multiply.

These degenerated plasma cells produce an excess of antibodies or antibody fragments. In connection with the plasma proteins, both hypoproteinemia and hyperproteinemia can also occur. In the first event, the concentration of plasma proteins falls below 66 grams per liter. In hyperproteinemia, on the other hand, the concentration is over 83 grams per liter. Hypoproteinemia can be caused, for example, by liver damage or malnutrition. Hyperproteinemia, on the other hand, is usually associated with inflammatory processes and can occur, for example, in the context of tuberculosis .

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.