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Plasma Proteins
Reading assignment Harper’s Biochemistry: PP 737-745
Dr. Zeyad El-Akawi Jreisat, M.D, M.A, Ph.D
Blood
• Solid elements:
– Red cells
– White cells
– Platelets
• Liquid medium:
– Plasma
Blood
Major Functions of Blood
- Respiration
- Nutrition
- Excretion
- Acid-base balance
- Water balance
- Body temperature regulation
- Defense
- Hormone transport and regulation of metabolism
- Metabolite transport
- Coagulation
Difference between
plasma and serum????
Serum = plasma - coagulation factors
Plasma Composition
• Water
• Plasma proteins
92%
7% (total 7.0-7.5 g/dL)
– Simple
– Conjugated
• Glycoproteins
• Lipoproteins
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Electrolytes (Na+, K+, Ca+2, Cl-, HCO3-)
Metabolites
Nutrients
Hormones
Other solutes
1%
Plasma proteins
• Most plasma proteins, with the exception of
immunoglobulins and protein hormones are synthesized in
the liver
• Plasma proteins are generally synthesized on membranebound polyribosomes
– Rough endoplasmic membrane → smooth endoplasmic membrane
→ Golgi apparatus → secretory vesicles → Plasma
• Almost all plasma proteins are glycoproteins
• Plasma proteins circulate in the blood and between the
blood and the extra-cellular tissue spaces. Their movement
occurs not only by passive diffusion through junctions
between capillary endothelial cells but by active transport
mechanisms and by pinocytosis and exocytosis
Plasma proteins
• Because of this movement, most extra-vascular fluids
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normally contain small amount of plasma proteins
The concentration of protein in the plasma is important in
determining the distribution of fluid between blood and
tissues
Many plasma proteins exhibit polymorphism
– Alpha1-antitrypsin, haptoglobin, transferrin,
ceruloplasmin and immunoglobulins
Each plasma protein has a characteristic half-life in the
circulation
Most plasma proteins are catabolized in the liver.
Plasma proteins
• Alterations in plasma proteins occurs in health and disease
• The levels of certain proteins in plasma increase during
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acute inflammatory states or secondary to certain types of
tissue damage
Some of these alterations have genetic origin, many more
reflect physiological or pathological processes
Variations in the amount or kinds of protein found in
plasma or extra-vascular fluids depend on many factors
– Genetic
– Physiological
– Pathological
Classification of plasma proteins based on
their function
• Antiproteases: antichymotrypsin, alpha1-antitrypsin,
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alpha2-macroglobulin, antithrombin
Blood clotting: various coagulation factors, fibrinogen
Enzymes:
– Function in blood; coagulation factors, cholinesterase
– Leakage from cells or tissues; aminotransferases
Hormones: Erythropoietin
Immune defense: immunoglobulins, complement proteins,
beta2-microglobulin
Involvement in inflammatory responses: Acute phase
response proteins (c-reactive proteins, alpha1-acid
glycoprotein)
Oncofetal: alpha-1 fetoprotein (AFP)
Classification of plasma proteins based on
their function
• Transport or Binding proteins:
– Albumin; various ligands, including bilirubin, free fatty acids, ions
(Ca+2), metals (Cu+2, Zn+2), metheme, steroids and other hormones,
drugs.
– Ceruloplasmin: contains Cu+2
– Corticosteroid-binding globulin: transcortin (binds cortisol)
– Haptoglobin: binds extracorpuscular hemoglobin
– Lipoproteins: chylomicrons, VLDL, LDL, HDL
– Hemopexin: binds heme
– Ritenol-binding protein: binds retinol
– Sex hormone-binding globulin: binds testosterone, estradiol
– Thyroid-binding globulin: binds T3, T4
– Transferrin: transport iron
– Transthyretin (prealbumin): binds T4 and forms a complex with
retinol-binding protein
Plasma proteins separation
• Separation of individual proteins from a complex mixture is
accomplished by the use of solvents or electrolytes or both to remove
different protein fractions in accordance with their solubility
characteristics.
• Salting out: a method for separation of plasma proteins using various
concentrations of
[Sodium or ammonium sulfate]
• Plasma proteins can be separated by this method into three groups
– Fibrinogen
– Albumin
– Globulins
Plasma proteins separation
• Electrophoresis:
– The most common method of analyzing plasma proteins
– Using different supporting medium, the most common
in clinical laboratories is cellulose acetate
(electrophoretogram)
– Separated proteins into five bands: albumin, alpha1,
alpha2, beta, and gamma fractions
– The amount of bands quantified by densitometric
scanning machine
Electrophoresis
Plasma protein electrophoresis
Quantified of plasma proteins by
densitometric scanning machine
Plasma proteins separation
• Antibodies:
– Specific plasma proteins are separated by specific
monoclonal antibodies fixed on stationary phase
(Column Chromatography)
– Allowing isolation of pure proteins from the complex
mixture present in plasma
Acute phase reactant proteins
**Concentration of these proteins rise significantly in acute
inflammation, chronic inflammation and cancer**
• Alpha1-antitrypsin (AAT): congenital deficiency may be
associated with emphysema or cirrhosis
• Alpha1-acid glycoprotein (AAG): binds cationic drugs and
hormones
• Haptoglobin (HAP): binds hemoglobin, reduced by
hemolysis
• Ceruloplasmin (CER): contains copper, antioxidant,
decreased in Wilson’s disease
• C4: Complement factor
• C3: Complement factor
• C-reactive protein (CRP): Nonspecific defense against
infectious agents
• Fibrinogen
**Stimulatory factors, Interleukin-1 (IL-1) and interleukin-6
(IL-6) at the gene level**
Plasma proteins
• Albumin:
– is the major protein of human plasma (3.4-4.7 g/dL)
– Approximately 40% of albumin is present in plasma and the other
60% in the extracellular space
– It synthesized in the liver as preproprotein
– The synthesis of albumin is depressed in a variety of diseases,
particularly those of the liver (decreased albumin/globulin ratio)
– Responsible for 75-80% of the osmotic pressure of human plasma
– Absence of albumin (analbuminemia) might caused by mutation
that affect splicing
– It binds many ligands (free fatty acids, calcium, certain steroid
hormones, bilirubin, tryptophan)
– It binds and transport drugs (sulfonamides, penicillin G,
dicumarol, aspirin)
– It transports copper
• Haptoglobin:
– Binds extracorpuscular hemoglobin preventing free hemoglobin
from entering the kidney
– Exist in three polymorphic forms, Hp1-1, Hp2-1, Hp2-2
– Low levels of haptoglobin are found in patients with hemolytic
anemias
– It is an acute phase protein and its plasma level is elevated in a
variety of inflammatory states
• Transferrin:
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Is a beta-1 globulin
It is a glycoprotein synthesized in the liver
Shuttles iron to sites where it is needed
Transferrin diminishes the potential toxicity of iron
The concentration of transferrin in plasma is approximately 300
mg/dL that can bind 300 µg of iron per deciliter (total iron-binding
capacity) of plasma
• Ferritin:
– Normally there is a little ferritin in human plasma
– In patients with excess iron, the amount of ferritin in plasma is
markedly elevated
– Index of body iron stores
– Synthesis of the transferrin receptors and that of ferritin are
reciprocally linked to cellular iron content
– Iron response elements
– Iron-responsive element-binding protein
• Hemosiderin:
– Partly degraded form of ferritin but still containing iron
• Primary hemochromatosis: is a common genetic disorder
characterized by excessive storage of iron in tissues leading to tissue
damage
• Secondary hemochromatosis: can occurs in the result of increased iron
levels by transfusion, intake, hemolysis
• Ceruloplasmin:
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It is an alpha-2 globulin
Binds copper
Low levels of this protein are associated with Wilson disease
It exhibits a copper-dependent oxidase activity
• Copper:
– Is a cofactor for certain enzymes including, amine oxidase, copperdependent superoxide dismutase, cytochrome oxidase, tyrosinase
– It is excess can cause problems because it can oxidize proteins and
lipids, bind to nucleic acids and enhance the production of free
radicals
– Metallothioneins: are a group of small proteins found in the cytosol
of cells particularly of liver, kidney, and intestine they control of
copper levels
• Menkes Disease: “kinky” or “Steely” hair disease
– Is due to mutations in the gene for a copper-binding P-type ATPase
leads to abnormality in copper metabolism
– X-linked
– Defect in copper exit from cells leads to its accumulation
– Involves the nervous system, connective tissue and vasculature
• Wilson Disease:
– Is due to mutations in the gene for a copper-binding P-type ATPase
results in the failure of copper to be excreted in the bile
– Copper toxicoses
• Alpha-1 antitrypsin deficiency: a serine protease inhibitor
– Is associated with emphysema and liver disease
– Synthesized by hepatocytes and macrophages