Plasma Proteins(Cont.) The plasma is the liquid medium of the blood(55-60%),in which the cell components namely erythrocytes,leukocytes,platelets and many proteins are suspended. Plasma – clotting factors=Serum Total concentration of plasma protein in blood is 7g/dl, which in total makes 7% of total blood volume.
General characteristicsof plasma proteins All the plasma proteins are synthesized in liver except gamma globulins which is synthesized by Plasma cells. Almost all the plasma proteins are glycoproteins. Some of the plasma proteins exhibit polymorphism(exist in different phenotypes) e.g α1 antitrypsin,transferrin and hepatoglobin.
The concentration of certain plasma proteins (acute phase proteins) increases in disease states such as inflamation and tissue damage.These include C-reactive proteins,hepatoglobin, fibrinogen and α1 antitrypsin.
Electrophoresis is the most commonly employed technique for the separation plasma proteins. Electrophoresis is used for the diagnosis of certain diseases e.g multiple myeloma,acute infections,Neprotic syndrome etc.
Plasma Proteins(Cont.) Albumins most abundant blood plasma protein. Concentration is 3.5-5.0g/dl Produced in the liver Normally constitutes about 60-80% of human plasma protein. Half life is of 20 days Examples In animals Serum albumin, ovalbumin,lactalbumin.
Plasma Proteins(Cont.) Functions Carriers for molecules of low water solubility including lipid soluble hormones, bile salts, un-conjugated bilirubin, free fatty acids (apo-protein), calcium ions, and some drugs like warfarin.
Plasma Proteins(Cont.) Metal Binding: A large proportion of zinc in serum is bound to albumin. Albumin binds other divalent cations, such as Ca, Mg, Mn, Cd, Co, and Ni. Fatty Acid Binding: Fatty acids, such as linoleic, linolenic and oleic acid are insoluble in aqueous solutions and must be delivered to cells by a carrier molecule.
Osmotic function Albumin contributes to 75-80% OF TOTAL PLASMA OSMOTIC PRESSURE(25 mm Hg).Thus albumin plays a predominant role in maintaing the blood volume and body fluid distribution. Decrease in plasma albumin levels results in fall in plasma osmotic pressure,leading to enhanced fluid retention in tissue spaces causing EDEMA.
Regulation of colloidal pressure Gaw: Clinical Biochemistry; Churchill Livingstone (1999), p. 44.
Plasma Proteins(Cont.) Mixed Disulfides or Albumin: Human and bovine albumins contain an unpaired sulfhydryl at position 34 in their primary sequences. This sulfhydryl group often forms a covalent link with other sulfhydryl molecules such as cysteine or glutathione. Protect these molecules from oxidation and improve their availability for cells.
Plasma Proteins(Cont.) Albumins (Cont.) Low albumin (hypoalbuminemia) may be caused by liver disease, nephrotic syndrome, burns, protein-losing enteropathy, malabsorption, malnutrition, pregnancy, genetic variations and malignancy. High albumin (hyperalbuminemia) is almost always caused by dehydration.
Plasma Proteins(Cont.) Globulin Some globulins are produced in the liver, while others are made by the immune system. High molecular weight Solubility and electrophoretic migration rates lower than for albumin Normal concentration in blood is 2 to 3.5 g/dl.
Plasma Proteins(Cont.) Globular protein. Protein electrophoresis is used to categorize globulins into the following four categories: Alpha 1 globulins Alpha 2 globulins Beta globulins Gamma globulins
Plasma Proteins(Cont.) Transferrin(β globulin) A glycoprotein polypeptide chain containing 679 amino acids Binds iron reversibly molecular weight of around 80 KDa transferrin protein loaded with iron binds to transferrin receptor transported into the cell
Plasma Proteins(Cont.) Each transferrin molecule has the ability to carry two iron ions in the ferric form (Fe3+). Protects the body against the toxic effects of free iron.
Plasma Proteins(Cont.) Increased serum transferrin level occurs in iron deficiency anemia. An absence of transferrin in the body occurs in a rare genetic disorder known as atransferrinemia.
Plasma Proteins(Cont.) Ceruloplasmin (Alpha 2 globulins) Copper-carrying protein Synthesized in the liver Carries 90% of the copper in our plasma Molecular weight 151KDa . Low Ceruloplasmin levels: hepatic disease, Wilsons disease. Elevated levels: pregnancy, acute and chronic inflammation
Plasma Proteins(Cont.) Fibrinogen Fibrous protein Involved in the clotting of blood Fibrin is made from fibrinogen Soluble plasma glycoprotein Synthesized by the liver 340 KDa glycoprotein
Plasma Proteins(Cont.) blood plasma is 1.5-4.0 g/L Hexamer containing two sets of three different chains (α, β, and γ), linked to each other by disulfide bonds. The N-terminal sections of these three chains contain the cysteines that participate in the cross-linking of the chains. The C-terminal parts of the α, β and γ chains contain a domain of about 225 amino-acid residues, which can function as a molecular recognition unit.
Haptoglobin(Alpha 2globulin) Acute phase protein. It binds with free hemoglobin(extracorpuscular hemoglobin) that spills into the plasma due to hemolysis. The Hp-Hb complex (155,000) cannot pass through glomeruli of kidney while free Hb (65,000) can. Hepatoglobin therefore prevents the loss of free hemoglobin into the kidney.
C-REACTIVE PROTEIN (CRP)• Major component of the acute phase response and amarker of bacterial infection.• Mediates the binding of foreign polysaccharides,phospholipids and complex polyanions, as well as theactivation of complement• <1 mg/mL in normal plasma• Slightly elevated levels of CRP are indicative ofchronic, low-grade inflammation and have beencorrelated with an increased risk of cardiovasculardisease .
Higher vertebrates including man,have evolved a defense system to protect themselves against the invasion of foreign substances a virus,a bacterium or a protein.The defense strategies of the body are collectively known as immunity.
CELLULAR IMMUNITY.Mediated by T cells. HUMORAL IMMUNITY.Mediated by immunoglobulins or antibodioes produced by the B cells.
Plasma Proteins(Cont.) Antibodies Also known as immunoglobulins Abbreviated as Ig Gamma globulin proteins General structure of all antibodies is very similar
Antibodies Proteins that recognize and bind to a particular antigen with very high specificity. Made in response to exposure to the antigen. One virus or microbe may have several antigenic determinant sites(epitopes), to which different antibodies may bind. Each antibody has at least two identical sites that bind antigen: Antigen binding sites. Valence of an antibody: Number of antigen binding sites. Most are bivalent. Belong to a group of serum proteins called immunoglobulins (Ig’s).
Antibody structure Disulfide bond Variable & Constant Regions Carbohydrate VL & CL VH & CH CL Hinge Region VL CH2 CH3 CH1 Hinge Region VH
Human ImmunoglobulinClasses IgG - Gamma heavy chains IgM - Mu heavy chains IgA - Alpha heavy chains IgD - Delta heavy chains IgE - Epsilon heavy chains
• L chains are one of two types•Designated κ and λ and only•one type is found in Ig.
• L and H chains are subdivided intovariable and constant regions.The regionsare composed of three-dimensionally folded,repeating segments called domains. An Lchain consists of one variable (VL) and oneconstant (CL) domain.Most H chains consistof one variable (VH) and three constant(CH)domains.(IgG and IgA have three CHdomains,whereas IgM and IgE have four.)
The variable regions areresponsible for antigenbinding ,whereasthe constant regions are responsiblefor various biologic functions eg,complement activation and binding tocell surface receptors.
Immunoglobulin Classes I. IgG Structure: Monomer Most abundant (75-80%). Can traverse blood vessels. Transfers mother’s immunity to fetus. Mediates foreign cell destruction by complement system.
Immunoglobulin Classes II. IgM J Structure: Pentamer Ch Percentage serum antibodies: 5-10% ain Location: Blood, lymph, B cell surface (monomer) C Half-life in serum: 5 days 4 Complement Fixation: Yes Placental Transfer: No Known Functions: First antibodies produced during an infection. Effective against microbes and agglutinating antigens.
Immunoglobulin Classes III. IgA Structure: Dimer Percentage serum antibodies: 10-15% Location: Secretions (tears, saliva, intestine, milk), blood and lymph. Predominant antibody in the clostrum. Half-life in serum: 6 days Known Functions: Localized protection of mucosal surfaces. Provides immunity to infant digestive tract.
Immunoglobulin Classes IV. IgD Structure: Monomer Percentage serum antibodies: 0.2% Location: B-cell surface, blood, and lymph Half-life in serum: 3 days Known Functions: In serum function is unknown. On B cell surface, act as B cell receptor, initiate immune response.
Immunoglobulin Classes V. IgE Structure: Monomer Percentage serum antibodies: 0.002% Location: Bound to mast cells and basophils throughout body. Blood. Placental Transfer: No Known Functions: Allergic reactions. The IgE molecules tightly bind with mast cells and release histamine and cause allergy.
Multiple Myeloma(Plasmacell cancer). Abnormal Ig production Malignancy of a single clone of plasma cells in bone marrow. Results in overproduction of Ig’s,mostely(75%) IgG,and in some cases(25%) IgA or IgM. Synthesis of normal immunoglobulins is diminshed causing diminshed immunity.
Bence jones proteins. These are light chains of immunoglobulins that are synthesized in excess. In about 20% of patients of multiple myeloma,Bence jones proteins are excreated in the urine which often damages the renal tubules.