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Plasma protein
Proteins present in blood serum
Proteins present in blood serum
Plasma proteins, sometimes referred to as blood proteins, are proteins present in blood plasma. They perform many different functions, including transport of hormones, vitamins and minerals in activity and functioning of the immune system. Other blood proteins act as enzymes, complement, components, protease inhibitors or kinin precursors. Contrary to popular belief, haemoglobin is not a blood protein, as it is carried within red blood cells, rather than in the blood serum.
Serum albumin accounts for 55% of blood proteins, is a major contributor to maintaining the oncotic pressure of plasma and assists, as a carrier, in the transport of lipids and steroid hormones. Globulins make up 38% of blood proteins and transport ions, hormones, and lipids assisting in immune function. Fibrinogen comprises 7% of blood proteins; conversion of fibrinogen to insoluble fibrin is essential for blood clotting. The remainder of the plasma proteins (1%) are regulatory proteins, such as enzymes, proenzymes, and hormones. All blood proteins are synthesized in liver except for the gamma globulins.
Families of blood proteins
| Blood protein | Normal level | % | Function | Albumins | Globulins | Fibrinogen | Regulatory proteins | Clotting factors |
|---|---|---|---|---|---|---|---|---|
| 3.5–5.0 g/dl | 55% | create and maintain osmotic pressure; transport insoluble molecules | ||||||
| 2.0–2.5 g/dl | 38% | participate in immune system | ||||||
| 0.2–0.45 g/dl | 7% | Blood coagulation | ||||||
| Regulation of gene expression | ||||||||
| Conversion of fibrinogen into fibrin |
Examples of specific blood proteins:
- Prealbumin (transthyretin)
- Alpha 1 antitrypsin (neutralizes trypsin that has leaked from the digestive system)
- Alpha-1-acid glycoprotein
- Alpha-1-fetoprotein
- alpha2-macroglobulin
- Gamma globulins
- Beta-2 microglobulin
- Haptoglobin
- Human Serum Albumin
- Ceruloplasmin
- Complement component 3
- Complement component 4
- C-reactive protein (CRP)
- Lipoproteins (chylomicrons, VLDL, LDL, HDL)
- Transferrin
- Prothrombin
- MBL or MBP
Clinical significance
Separating serum proteins by electrophoresis is a valuable diagnostic tool, as well as a way to monitor clinical progress. Current research regarding blood plasma proteins is centered on performing proteomics analyses of serum/plasma in the search for biomarkers. These efforts started with two-dimensional gel electrophoresis efforts in the 1970s, and in more recent times this research has been performed using LC-tandem MS based proteomics. The normal laboratory value of serum total protein is around 7 g/dL.
Scientists are able to identify blood proteins using Photo-affinity labeling, a means of using photo-reactive ligands as a labeling agent to identify targeted proteins.
References
- Clinical Chemistry : a laboratory perspective / [edited by] Wendy Arneson, Jean Brickell.
References
- (2013-01-01). "Chapter 18 - Clinical Pathology in Non-Clinical Toxicology Testing". Academic Press.
- (1977). "High Resolution Two-Dimensional Electrophoresis of Human Plasma Proteins". Proceedings of the National Academy of Sciences.
- Adkins JN. (2002). "Toward a human blood serum proteome: analysis by multidimensional separation coupled with mass spectrometry". Molecular & Cellular Proteomics.
- (January 2016). "Large-scale inference of protein tissue origin in gram-positive sepsis plasma using quantitative targeted proteomics". Nat Commun.
- (November 2013). "Photoaffinity labeling of plasma proteins". Molecules.
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