Plasma proteins

PLASMA PROTEINS
Department of Biochemistry, KMC, DuwakotSaturday, April
04, 2015
Rajesh Chaudhary 1

Biomedical importance
Function Example
Transport Thyroxine-binding globulin (thyroid
hormones)
Apolipoproteins (cholesterol, triglyceride)
Humoral immunity Immunoglobulins
Maintenance of oncotic pressure All proteins, particularly albumin
Enzymes Renin, coagulation factors, complement
proteins
Protease inhibitors a1-antitrypsin (acts on protease)
Buffering All proteins
Functions of plasma proteins
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Measurement of Plasma protein
 Total plasma proteins vary in concentration due to
three factors:
 1. Synthesis
 2. Removal
 3. Volume of distribution
 Posture
 Application of tourniquet
 Change in major proteins such as “Albumin” and/or
“Immunoglobulins”.
 State of hydration.
Saturday, April 04, 2015Rajesh Chaudhary
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Plasma proteins
 Plasma contains complex mixture of proteins.
 E.g.: glycoproteins and lipoproteins.
 Thousands of antibodies.
 Can be studied only after separating it.
 Methods to separate: salting-out method – by using solvents or
electrolytes.
 Plasma proteins can be separated into three major groups:
Fibrinogen, Albumin and Globulin.
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Plasma proteins
Total concentration of plasma
proteins: 7.0 – 7.5 g/dL
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Plasma protein or Serum protein ?
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What sample is used during separation of proteins –
either plasma or serum and why?
+ve -ve
Point of application

Most common method --
ELECTROPHORESIS
 Depends on the supporting medium used.
 Supporting mediums can be: agarose gel, polyacrylamide
gel, cellulose acetate membrane.
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Plasma proteins are classified according to their electrophoretic mobility.
Factors affecting mobility / movement of protein in separating medium?

Electrophoresis
Why to use a more sophisticated supporting medium?
Resolution !
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Densitometer graphical quantitation

Concentration of plasma protein
 …is important in determining the distribution of fluid between
blood and tissue.
 In arterioles: hydrostatic pressure is ~37 mm Hg.
 Interstitial pressure: 1 mm Hg (opposing it).
 The osmotic pressure exerted by plasma protein: 25 mm Hg.
 In venues the hydrostatic pressure is ~17 mm Hg with oncotic
and interstitial pressure as described above.
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Plasma proteins
(Plasma proteins have been studied extensively)
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 1. Most plasma proteins are synthesized in the liver.
 2. Plasma proteins are generally synthesized on membrane-bound
polyribosomes.
 3. Almost all plasma proteins are glycoproteins.
 4. Many plasma proteins exhibit polymorphism.
 5. Each plasma proteins has a characteristic half-life in the circulation.
 6. The levels of certain proteins in plasma increase during acute phase.

Causes of changes in total plasma
protein concentration
Increase Decrease
Hypergammaglobul
inemia
Protein synthesis
Malnutrition and
malabsorption liver
disease, humoral
immunodeficiency
protein synthesis
Artefactual
Haemoconcentration
due to stasis of blood
during venepuncture
Over-hydration
increased capillary
permeability
volume of
distribution
Dehydration
Volume of
distribution
Protein-losing states
catabolic states
excretion /
catabolism
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Major plasma proteins
 1. Albumin
 2. Globulin
 2.1. a-globulin
 2.1.1. a1-globulin / a1-antitrypsin
 2.1.2. a2-globulin / Haptoglobulin
 a2-macroglobulin
 2.2. b-globulin
 2.2.1. Transferrin
 2.3. g-globulin
 3. Acute phase proteins
 4. Other plasma proteins
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Albumin
 69 kDa in size and is a major protein in human plasma (3.4 –
4.7 g/dL).
 ~60% of total plasma protein is Albumin.
 40% is present in plasma and remaining 60% in extracellular
space.
 12 g/day of albumin is produced.
 Albumin production is reduced in live disease.
 Mature human albumin: 585 AA, single polypeptide chain, 17
disulfide bonds.
 Shape: ellipsoidal shape, thus doesn’t increase viscosity
plasma.
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Analbuminemia
 Condition in which human lacks albumin.
 Reason: because of mutation in gene splicing.
 Patient shows moderate edema.
 Binds with several forms of ligands.
 E.g. Calcium, steroid hormones, FFA, bilirubin etc.
 Plays an important role in copper transport in body.
 Used in treatment of hemorrhagic shock but it’s controversial.
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Haptoglobulin (Hp)
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 Binds extracorpuscular hemoglobin (Hb) in tight
noncovalent complex (Hb-Hp).
 Amount: 40-180 mg of hemoglobin-binding capacity per
deciliter.
 Molecular weight of Hb: 65 kDa.
 Molecular weight of Hp: 90 kDa.
 Total = 155 kDa.
 Haptoglobulin exists in three polymorphic forms: Hp 1-1,
Hp 2-1, and Hp 2-2.
 The level of haptoglobulin falls in hemoglytic anemia.
How does Hp level falls in hemolytic anemia?

Transferrin / b1-globulin
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 Glycoprotein with 76 kDa of size, having 20 polymorphic
forms is synthesized in liver.
 Have 20 polymorphic forms.
 Transfers 2 moles of Fe3+ per mole of transferrin.
 Approximately 200 billion red blood cells (about 20 mL) are
catabolized per day, releasing about 25 mg of iron into the
body.
 Iron consumed through diet is absorbed as Fe2+.
 Free iron is toxic but diminishes potential toxicity and also
directs where it is required.
 Total concentration of transferring in plasma 300 mg/dL.

Ceruloplasmin / a2-globulin
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 Molecular weight: 160 kDa.
 Blue in color because of high copper content.
 Carries 90% of copper in plasma, 10% is carried by
Albumin.
 Exhibit copper-dependent oxidase activity.
 Level of Ceruloplasmin decreases in liver disease – Wilson’s
disease (hepatolenticular degeneration) and Menkes
disease.
 Body total copper content is 100 mg located mostly in bone,
liver, kidney, and muscle.
 Daily consumption is 2-4 mg, out of which 50% is absorbed
in upper small intestine.

Comparison of Menkes and Wilson
disease
Sunday, April 05, 2015Rajesh Chaudhary
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Menkes Disease Wilson Disease
Location of gene Xq13.3 13q14.3
Inheritance X-linked recessive Autosomal recessive
Gene product Cu2+-binding p-type ATPase Cu2+-binding p-type ATPase
Expression In all tissues except liver Liver, Kidney, Placenta
Mutations Variety Variety
Onset At birth Late childhood
Clinical findings Cerebral degeneration,
abnormal hair, early death
Liver diesase, neurological
signs, can survive late
adulthood

a1-antitrypsin / a1-antiproteinase
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 Molecular weight: 52 kDa.
 Single polypeptide chain of 394 AA. Major
component of a1-fraction.
 Synthesized by macrophages and hepatocytes and
a principle “serine protease inhibitor”.
 Inhibits trypsin, elastase and certain other
proteases.
 Have 75 polymorphic forms.
 Its deficiency results in emphysema.

a1-antitrypsin / a1-antiproteinase
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a2-macroglobulin
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 Large glycoprotein with molecular weight 720 kDa.
 Consists of 4 subunits each subunits with 180kDa.
 Comprise of 8-10% of total plasma proteins.
 Approximately 10% of total copper in plasma is
transported by a2-macroglobulin, remainder is
transported by albumin.
 Major panprotease inhibitor.
 Cleared from plasma after binding to receptor located in
many cell types.

1. Harper’s Biochemistry, 25th. Edition
2. Mark’s Basic Medical Biochemistry, 8th.
Edition
3. Clinical Chemistry, William J Marshal, 6th.
Edition
References
Saturday, April 04, 2015
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Rajesh Chaudhary

Plasma proteins

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