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Plasma proteins
Plasma contains proteins that perform important functions like maintaining pH and colloid osmotic pressure. The most abundant protein is albumin, which makes up around 75% of plasma's colloid osmotic pressure. Other major classes of plasma proteins include globulins such as alpha-1 globulins containing thyroxine-binding globulin and alpha-1-antitrypsin; alpha-2 globulins containing ceruloplasmin and haptoglobin; beta-globulins containing transferrin; and gamma-globulins which are antibodies. These proteins transport substances like vitamins, minerals, lipids, and hormones or help in coagulation, immune defense, and acute phase responses.
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Plasma proteins
- 1. Plasma Proteins R. C.Gupta Professor and Head Dept. of Biochemistry National Institute of Medical Sciences Jaipur, India
- 2. BLOOD (45% cells, 55% plasma) Red bloodcells (erythrocytes) White blood cells (leukocytes) Platelets (thrombocytes) Plasma (water and solutes)
- 3. EMB-RCG Plasma is bloodminus the cells Plasma contains water and a number of solutes The most abundant solutes are proteins
- 4. The total proteinconcentration in plasma is 6-8 gm/dl Plasma contains a large number of proteins Some are present in very minute amounts e.g. hormones and enzymes These are not considered as plasma proteins
- 5. EMB-RCG Some proteins arepresent in plasma in significant concentrations They perform their functions in plasma These are called plasma proteins
- 6. EMB-RCG Some functions ofplasma proteins are of a general nature: Maintenance of pH Maintenance of colloid osmotic pressure
- 7. Some specialised functionsare performed by specific proteins: • Transport of hormones, vitamins, minerals, lipids etc • General defense against foreign invaders • Specific defense against antigens • Coagulation of blood • Fibrinolysis
- 8. EMB-RCG Plasma proteins areusually fractionated by electrophoresis Fractionation of plasma proteins
- 9. EMB-RCG Electrophoresis separates plasma proteins into: Albumin a1-Globulins a2-Globulins b-Globulins g-Globulins ‒Albumin ‒ a1-Globulins ‒ a2-Globulins ‒ b-Globulins ‒ g-Globulins ‒ +
- 10. EMB-RCG More sensitive techniquesseparate the b-globulins into b1- and b2-globulins Albumin Globulins b1 b2a1 a2 g
- 11. EMB-RCG Each globulin fractioncomprises a number of proteins All the plasma proteins except g-globulins are synthesized in liver The g-globulins are synthesized in and secreted by plasma cells
- 12. Most abundant proteinin plasma Concentration is 3.5 - 5.5 gm/dl Synthesized exclusively in liver EMB-RCG Albumin Half-life approximately 20 days
- 13. COP of plasmais mostly due to proteins EMB-RCG Proteins are the major colloids in plasma Albumin is responsible for 75% of COP of plasma Colloid osmotic pressure (COP) 75% 25% Albumin Others
- 14. Albumin is madeup of a single polypeptide chain of 585 amino acids Its molecular weight is 69,000 EMB-RCG
- 15. Functions of albumin •Vehicle for transferring amino acids from liver to extra-hepatic tissues • Carrier of free fatty acids, calcium, copper, unconjugated bilirubin, lipophilic hormones etc • Also carries drugs e.g. aspirin, phenytoin, dicoumarol, sulphonamides etc
- 16. Liver diseases dueto decreased synthesis of albumin Renal diseases due to loss of albumin in urine Kwashiorkor due to severe dietary deficiency of proteins Hypoalbuminaemia can occur in:
- 17. Hypoalbuminaemia decreases the colloidosmotic pressure of plasma This can result in oedema EMB-RCG
- 18. Another protein thatcan bind all the ligands that albumin can bind Smaller than albumin and moves ahead of albumin on electrophoresis Present in much lower concentration than albumin EMB-RCG Prealbumin
- 19. Globulins EMB-RCG Globulins comprise several fractions: •a1-Globulins • a2-Globulins • b-Globulins • g-Globulins
- 20. a1-Globulins EMB-RCG a1-Globulins include: • a-Lipoprotein(HDL) • Thyroxine-binding globulin (TBG) • Corticosteroid-binding globulin (CBG) • Retinol-binding protein (RBP) • a1-Antitrypsin • a1-Acid glycoprotein • a-Fetoprotein
- 21. EMB-RCG a-Lipoprotein (HDL) transports cholesterolfrom periphery to liver Thyroxine-binding globulin (TBG) transports thyroid hormones Corticosteroid-binding globulin (CBG) transports steroid hormones Retinol-binding protein (RBP) transports vitamin A
- 22. EMB-RCG a1-Antitrypsin is nowcalled a1-anti- proteinase It is an inhibitor of serine proteases e.g. trypsin, elastase etc An important function of a1-antitrypsin is to prevent destruction of elastin in lungs a1-Antitrypsin
- 23. EMB-RCG Small amounts ofelastase are released in lungs continuously from naturally dying neutrophils Much larger amounts are released in pulmonary infection as neutrophils accumulate at the site of infection a1-Antitrypsin binds to elastase and prevents its proteolytic action
- 24. EMB-RCG An inherited deficiencyof a1-antitrypsin results in unchecked action of elastase on elastin Destruction of elastin decreases the elasticity of lungs resulting in emphysema
- 25. EMB-RCG Smokers with a1-antitrypsindeficiency are particularly prone to emphysema Cigarette smoke converts a critical methionine residue of a1-antitrypsin into methionine sulphoxide This prevents the binding of a1-antitrypsin to elastase
- 26. EMB-RCG a1-Acid glycoprotein isanother acute phase protein These are released in acute infections a1-Antitrypsin belongs to the group of acute phase proteins (or reactants)
- 27. EMB-RCG Acute phase proteinshelp the immune system in fighting against infectious agents They also help in clearing up the debris from the site of infection Release of acute phase proteins is induced by some interleukins secreted by macro- phages and T lymphocytes
- 28. EMB-RCG a-Fetoprotein (AFP) issynthesized in foetal life but not after birth It is synthesized in some cancers as the cancer cells revert to the undifferentiated type Therefore, a-fetoprotein is used as a tumour (cancer) marker a-Fetoprotein
- 29. a2-Globulins EMB-RCG a2-Globulins include: • Ceruloplasmin •Haptoglobin • a2-Macroglobulin
- 30. EMB-RCG A copper-containing protein 90%of plasma copper is tightly bound to ceruloplasmin Rest is loosely bound to albumin Ceruloplasmin
- 31. EMB-RCG Ceruloplasmin was believedto be a copper carrier in the past But copper bound to ceruloplasmin is not released easily Hence the carrier function is performed by albumin
- 32. EMB-RCG Ceruloplasmin possesses ferroxidase activity Itsreal function is to oxidise ferrous iron to the ferric form Is also an acute phase protein
- 33. Another acute phaseprotein Can bind free haemoglobin (Hb) Haptoglobin
- 34. Hb released intoplasma from ruptured RBCs can easily pass through glomeruli This can clog tubular lumen It can also cause loss of iron from the body
- 35. EMB-RCG Haptoglobin binds freehaemoglobin Combined size of the two is too big to pass through glomeruli This prevents leakage of haemoglobin into glomerular filtrate and loss of iron
- 36. EMB-RCG a2-Macroglobulin is ageneral protease inhibitor It inhibits coagulation and fibrinolysis a2-Macroglobulin levels are increased in nephrotic syndrome a2-Macroglobulin
- 37. b-Globulins EMB-RCG b-Globulins include: • b-Lipoprotein(LDL) • Transferrin • Complement components C1q and C3 • Haemopexin • C-Reactive protein (CRP)
- 38. EMB-RCG b-Lipoprotein (LDL) transportscholesterol from liver to periphery Transferrin transports iron Complement components help the immune system in fighting against infections
- 39. EMB-RCG Binds free haem Ifhaem enters plasma, it is freely filtered by the glomeruli This can lead to loss of iron from the body Haemopexin
- 40. EMB-RCG Haemopexin binds haemreleased in plasma This prevents glomerular filtration of haem and loss of iron
- 41. EMB-RCG So named becauseit reacts with C polysaccharide C Polysaccharide is present in the capsule of pneumococci C-Reactive protein (CRP)
- 42. EMB-RCG CRP is anacute phase protein It can stimulate the classic complement cascade upon entry of any pathogen in the body Raised CRP concentration in plasma shows the presence of some infection in the body
- 43. EMB-RCG g-Globulins act asantibodies Also known as immunoglobulins as they perform an immune function g-Globulins
- 44. EMB-RCG Is an acutephase protein Is converted into fibrin during coagulation Several fibrin molecules aggregate to form the clot Fibrinogen Is one of the coagulation factors
- 45. Fibrinogen Fibrin monomer Fibrin dimer Fibrinpolymer Fibrin polymer cross-linked