Plasma proteins 42
Plasma proteins Quantitatively, proteins are the most important part of the soluble components of the blood plasma. concentrations of between 60 and 80 g L 1, they constitute approximately 4% of the body s total protein. Their tasks include transport, regulation of the water balance, hemostasis, and defence against pathogens. Some 100 different proteins occur in human blood plasma.
Plasma proteins are broadly divided into5 fractions: - albumins α1, α2, β and γ-globulins Table 1. Most plasma proteins are synthesized by the liver except antibodies and hormones With the exception of albumin, almost all plasma proteins are glycoproteins. 12 Proteins Comprise ~96% of the Protein Mass in Plasma 3
Table 1 classes of most common plasma proteins
1-Albumin The most frequent protein in the plasma, at around 45 g L 1, is albumin. Common functions of albumin: 1-Due to its high concentration, albumin plays a crucial role in maintaining the bloods colloid osmotic pressure (oncotic pressure). The oncotic pressure prevents fluid leaking out of capillaries in to tissue fluid. 2-represents an important amino acid reserve for the body. 3-Albumin has binding sites for apolar substances and therefore functions as a transport protein for long-chain fatty acids, Bilirubin, drugs, and some steroid hormones and vitamins Bilirubin is toxic if it is free, by binding with albumin it looses its toxicity.
4- serum albumin binds Ca 2+ and Mg 2+ ions and make them inactive. The albumin fraction also includes transthyretin (prealbumin), which together with other proteins transports the hormone thyroxine and its metabolites.
A number of pathological conditions causes low conc of albumin in Blood: Liver disease Malnutrition and malabsorption Nephrotic syndrome Protein losing entropathy Acute phase reaction Clinical uses of urine albumin measurements Clinical use of serum albumin measurements A low serum albumin is not an indication of any Underlying disease, however further investigation must be made for underlying diseases. Most diagnostic use of Serum albumin is to determine serum calcium
Albumin is the principle protein in urine a condition termed microalbuminurea Also known as: Microalbumin; ACR; UACR Formal name: Urine Albumin and Albumin/Creatinine Ratio Which describes urine albumin concentrations 3 250mg/L. Microblumin urea is very useful to monitor increased risk diabetic nephropathy. The urine albumin test or albumin/creatinine ratio (ACR) is used to screen people with chronic conditions, such as diabetes and hypertension, that put them at an increased risk of developing kidney disease. The urine creatinine concentration reflects renal flow as the creatinine output / day of an individual is quite constant.
2-Alpha 1-antitrypsin It is a serine protease inhibitor, it protects tissues from enzymes of inflammatory cells Clinical uses of AAS measurements It is performed to investigate neonatal janudice and patients with liver diseases 3-Haptoglobin Hepatoglobin is a Hb binding protein in plasma In normal conditions, Hb is packaged with in the RBCs. Free Hb occur in low conc in the plasma, If it is high in the plasma it can precipitate in the kidney tubules And damage them. A condition called intravascular haemolysis causes the lyse of the RBCs in blood vessels and the release of HB. Clinical use of haptoglobin: It is used to diagnose anaemia or jaundice
4-Caeruloplasmin Is a large protein which contain about 90% of copper content in plasma and transport copper. It is a ferro oxidase (changes Fe +2 to Fe +3 ) It is essential for the absorption of Iron from digested food by the Small intestine. Iron is absorbed in the Fe +2 state but can only bind to transferrin in The Fe +3 state Clinical use For the investigation of* wilson s or menkes disease The test is usually accompanied by the measurement of copper conc. In menekes disease both copper and caeruloplasmin are low. In wilsons disease the serum copper and caeruloplasmin are usually low and the concentration of copper in solid body tissues Are always high.
*Wilson s disease results from the deficiency of copper transport protein And the linkage of copper to caeruloplasim. The result is accumulation of copper in liver and therefore copper Leaks out from the liver and are deposited in other body tissues Especially the liver and the brain causing lots of complications *The Menkes disease results from impaired copper absorption in the Small intestine which causes low serum copper concs. in plasma Low copper impairs enzymes that need copper to be activated and results in nuerodegeneration and death within the first decades of life.
5- C-reactive protein (CRP) is a protein whose concentration increases dramatically during An inflammatory event Once bound to bacteria it activates the immune system to attack Clinical use It is an ideal marker of inflammation It is used to monitor infection A special type of CRP test, the high-sensitivity CRP test (hs-crp), is used to find out if you might have a sudden heart problem, such as a heart attack. Inflammation can damage the inner lining of the arteries and make having a heart attack more likely. But the connection between high CRP levels and heart attack risk is not understood very well. 12
6-Immunoglobins Some important immunological terms Anti body: also called immunoglobulin, is protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies are produced by specialized white blood cells called B lymphocytes or B cells.
Clinical use of Ig measurements High level of Igs IgG IgM IgA IgE High IgG may mean a long-term (chronic) infection, such as HIV High IgM Liver disease, primary biliary cirrhosis Alcoholic liver cirrhosis multiple myeloma is present. IgA also get higher in some autoimmune diseases, such as rheumatoid arthritis a parasite infection is present Low level of Igs IgG IgM IgA susceptibility to bacterial infections Also used to monitor those patients treated with immunotherapy multiple myeloma, some types of leukemia leukemia, kidney damage (nephrotic syndrome), a problem with the intestines (enteropathy