Plasma proteins, sometimes referred to asblood proteins, areproteins present inblood plasma. They perform many different functions, including transport ofhormones,vitamins andminerals in activity and functioning of theimmune system. Other blood proteins act asenzymes, complement, components,protease inhibitors orkinin precursors. Contrary to popular belief,haemoglobin is not a blood protein, as it is carried withinred blood cells, rather than in the bloodserum.
Serum albumin accounts for 55% of blood proteins,[1] is a major contributor to maintaining theoncotic pressure of plasma and assists, as a carrier, in the transport of lipids andsteroid hormones.Globulins make up 38% of blood proteins and transportions, hormones, and lipids assisting inimmune function.Fibrinogen comprises 7% of blood proteins; conversion of fibrinogen to insolublefibrin is essential forblood clotting. The remainder of the plasma proteins (1%) areregulatory proteins, such as enzymes,proenzymes, andhormones. All blood proteins are synthesized inliver except for thegamma globulins.[1]
| Blood protein | Normal level | % | Function |
|---|---|---|---|
| Albumins | 3.5–5.0 g/dl | 55% | create and maintainosmotic pressure; transport insoluble molecules |
| Globulins | 2.0–2.5 g/dl | 38% | participate inimmune system |
| Fibrinogen | 0.2–0.45 g/dl | 7% | Bloodcoagulation |
| Regulatory proteins | <1% | Regulation of gene expression | |
| Clotting factors | <1% | Conversion of fibrinogen into fibrin |
Examples of specific blood proteins:[citation needed]
Separatingserum proteins byelectrophoresis is a valuablediagnostic tool, as well as a way to monitorclinical progress. Current research regardingblood plasma proteins is centered on performingproteomics analyses of serum/plasma in the search forbiomarkers. These efforts started withtwo-dimensional gel electrophoresis[2] efforts in the 1970s, and in more recent times this research has been performed using LC-tandem MS[3][4] basedproteomics. The normal laboratory value ofserum total protein is around 7 g/dL.[citation needed]
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.[5]
