Plasma protein
Proteins present in blood serum
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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
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
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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.