PLASMA PROTEINS M.Prasad Naidu MSc Medical Biochemistry, Ph.D,.

INTRODUCTION Total blood volume is 4.5-5 litres. If blood containing anticoagulants (e.g.heparin , potassium oxalate) is centrifuged , the plasma separates out as a supernatant while the cells remain at the bottom. About 55-60% of blood is plasma The packed cell volume or hematocrit is about 40-45%

Introduction It constitutes about 55% of the blood volume. Plasma is the clear straw coloured fluid portion of the blood minus its cellular elements. It constitutes about 55% of the blood volume. Serum is plasma minus clotting factors (fibrinogen & prothrombin ). The defribrinated plasma is called serum

COMPOSITION OF PLASMA Is the main constituent of Plasma – 91% PLASMA contains the following composition: WATER: Is the main constituent of Plasma – 91% SOLIDS: 9% of the plasma (1% inorganic molecules & 8% organic molecules)

OTHER ORGANIC MOLECULES Carbohydrates : Glucose ( 100-120 mg%) Fats : neutral fats, phospholipids (150-300mg%) Cholesterol (150-240 mg%)

Non protein nitrogenous substances : Non protein nitrogenous substances : ammonia, amino acids, creatine, creatinine (0.6-1.2 mg%) xanthine, hypoxanthine, urea (20-40 mg%) & uric acid (2-4 mg%). Hormones enzymes & antibodies.

Inorganic molecules are sodium, potassium, calcium, magnesium, chloride, iodide, iron, phosphates & copper. Gases presents in the plasma are O2 ,Co2,& N2 .

plasma proteins… - forms 7% of the solids in plasma - their normal valves – 7.4 gm% ranges from (6.4 – 8.3 gm%) INCLUDES: ALBUMIN GLOBULINS FIBRINOGEN

NORMAL VALUES Total protein content of normal plasma is 6 - 8 g/100ml The plasma proteins consist of : 1)albumin (3.5-5 g/dl) 2)globulins (2.5-3.5 g/dl) 3)fibrinogen (200-400 mg/dl)

The albumin : globulin ratio is usually between 1.2 :; 1 to 1.5 :1 Almost all plasma proteins , except immunoglobulins are synthesized in liver

SEPARATION OF PLASMA PROTEINS USING SALTS In clinical laboratory, separation is usually done by salts. Thus , fibrinogen is precipitated by 10% and globulins by 22% concentration of sodium sulphate Ammonium sulphate will precipitate : albumin by full-saturation globulin by half-saturation

ESTIMATION OF PLASMA PROTEINS In clinical laboratory , total proteins of patients are estimated by Biuret method. Albumin is quantitated by Bromo cresol green (BCG) method , in which the dye is preferentially bound with albumin , and the colour intensity is measured colourimetrically.

OTHER METHODS: Lowry’s method Kjeldahl’s method Dye-binding method UV-absorption method

ELECTROPHORESIS The most common method of analyzing plasma proteins is by electrophoresis. The term electrophoresis refers to the movement of chargeD particles through an electrolyte when subjected to an electric field

In clinical laboratory , cellulose acetate is widely used as a supporting medium. Its use permits resolution , after staining , of plasma proteins into five bands , designated albumin , α1 , α2 , β and γ fractions, respectively

The stained strip of cellulose acetate is called electrophoretogram. The amounts of these five bands can be conveniently quantified by use of Densitometric scanning machines. Characteristic changes in the amounts of one or more of these five bands are found in many diseases.

ABNORMAL PATTERNS IN CLINICAL DISEASES Various abnormalities can be identified in the electrophoretic pattern 1) CHRONIC INFECTIONS: The gammaglobulins are increased

2)MULTIPLE MYELOMA : In para-proteinemias , a sharp spike is noted and is termed as M-band. This is due to monoclonal origin of immunoglobulins

PRIMARY IMMUNE DEFICIENCY : The gamma globulin fraction is reduced NEPHROTIC SYNDROME : All proteins except very big molecules are lost through urine , and α-2-fraction will be very prominent

CIRRHOSIS OF LIVER : Albumin synthesis by liver is decreased , with a complementary excess synthesis by globulins by reticuloendothelial system

CHRONIC LYMPHATIC LEUKEMIA: Gamma globulin fraction is reduced ALPHA-1-ANTITRYPSIN DEFICIENCY: The alpha-1 band is thin or even missing

ALBUMIN Albumin (69 kDa) is the major protein in human plasma(3.4-4.7 g/dl) It makes up approximately 60% of the total plasma protein. About 40% of albumin is present in the plasma, and the other 60% is present in the extracellular space.

The liver produces about 12g of albumin per day , representing about 25% of total hepatic protein synthesis Albumin can come out of vascular compartment. So albumin is present in CSF and interstitial fluid.

FUNCTIONS OF ALBUMIN 1)COLLOID OSMOTIC PRESSURE OF PLASMA: The total osmolality of serum is 278-305 mosmol/kg. This is exerted mainly by salts, which can pass easily from intravascular to extravascular space. Therefore, the osmotic pressure exerted by electrolytes inside and outside the vascular compartments will cancel each other.

But proteins cannot easily escape out of blood vessels, and therefore , proteins exert the ‘effective osmotic pressure’. It is about 25mm Hg, and 80% of it is contributed by albumin. The maintenance of blood volume is dependent on this effective osmotic pressure

Regulation of colloidal pressure Gaw: Clinical Biochemistry; Churchill Livingstone (1999), p. 44.

TRANSPORT FUNCTION: Albumin is the carrier of various hydrophobic substances in the blood such as: i)bilirubin & non-esterified fatty acids ii)drugs (sulpha,aspirin,salicylate,) iii)hormones(steroid hormones,thyroxine) iv)metals (calcium,copper,heavy metals)

3)BUFFERING ACTION : Albumin has maximum buffering capacity amongst all proteins It has a total of 16 histidine residues which contribute to this buffering action.

4)NUTRITIONAL FUNCTION: All tissue cells can take up albumin by pinocytosis. It is then broken down to amino acid level. So albumin may be considered as the transport form of essential amino acids from liver to extrahepatic cells.

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