Blood proteins

Blood proteins, also termed plasma proteins, are proteins present in blood plasma. They serve many different functions, including transport of lipids, 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.

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[1] efforts in the 1970s and in more recent times this research has been performed using LC-tandem MS[2][3][4] based proteomics. The normal laboratory value of serum total protein is around 7 g/dL.

## Families of blood proteins

Blood protein | Normal level | % | Function

|
|
|

Albumins | 3.5-5.0 g/dl | 55% | create and maintain osmotic pressure; transport insoluble molecules
Globulins | 2.0-2.5 g/dl | 38% | participate in immune system
Fibrinogen | 0.2-0.45 g/dl | 7% | Blood coagulation
Regulatory proteins |  | <1% | Regulation of gene expression
Clotting factors  |  | <1% | 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
* Ceruloplasmin
* Complement component 3
* Complement component 4
* C-reactive protein (CRP)
* Lipoproteins (chylomicrons, VLDL, LDL, HDL)
* Transferrin
* Prothrombin
* MBL or MBP

## Notes

1. ↑ "High Resolution Two-Dimensional Electrophoresis of Human Plasma Proteins". Proceedings of the National Academy of Sciences 74 (12): 5421–5425. 1977. doi:10.1073/pnas.74.12.5421. PMID 271964.
2. ↑ Adkins JN (2002). "Toward a human blood serum proteome: analysis by multidimensional separation coupled with mass spectrometry". Molecular & Cellular Proteomics 1 (12): 947–955. doi:10.1074/mcp.M200066-MCP200. PMID 12543931.
3. ↑ Malmström, E; Kilsgård, O; Hauri, S; Smeds, E; Herwald, H; Malmström, L; Malmström, J (January 2016). "Large-scale inference of protein tissue origin in gram-positive sepsis plasma using quantitative targeted proteomics". Nat Commun 7: 10261. doi:10.1038/ncomms10261. PMID 26732734.
4. ↑ Geyer, PE; Kulak, NA; Pichler, G; Holdt, LM; Teupser, D; Mann, M (March 2016). "Plasma Proteome Profiling to Assess Human Health and Disease". Cell Syst 2 (3): 185–95. doi:10.1016/j.cels.2016.02.015. PMID 27135364.

## References

* Clinical Chemistry : a laboratory perspective / [edited by] Wendy Arneson, Jean Brickell.

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