Download Proteins in body fluids

Proteins in body fluids
Function of proteins
Overview of amino acids catabolism
Urea cycle
Plasma proteins
Albumin and globulins
Serum total proteins
CSF total protein
Urine protein
Bence-Jones protein
Function of proteins
 Proteins are derivatives of high molecular weight polypeptides. Functionally ,
proteins exhibit diversity . In cell, their main functions are the following
I. To act as enzymes.
II. To act as lubricants
III. To act as structural materials.
IV. To act as carrier molecules ….etc.
The capacity of the living organisms to store proteins is limited and relatively small
when compared to their capacity for storing carbohydrates and fats.
Proteins are, however, stored under special conditions as egg and seeds.
Proteins are of paramount importance because of the fact that they posses peculiar
chemical and physico-chemical properties.
1)
All enzymes are made up of proteins.
2)
May of hormones are proteinous in nature for instance insulin, glucagon, oxytocin,
vasopressin…..etc.
3)
They serve as building block units for subcellular, cellular and organic structures.
4)
They act as defence against infections by way of protein antibodies.
5)
They involved in blood clotting through thrombin, fibrinogen, and other protein factors.
6)
They perform hereditary transmission by way of nucleoproteins found in the cell nucleus.
7)
They act as buffers .
1)
They help in the transport of oxygen and carbon dioxide by haemoglobin and certain
special enzymes which are found in red blood cells.
Overview of amino acids
catabolism
The amino group and the carbon
skeleton take separate but
interconnected pathways.
The connection between urea
cycle and citric acid cycle.
The pathways of amino acids
catabolism are the same in most
organisms.
Dietary protein is enzymatically
degraded to amino acids
The degradation of ingested proteins to their
amino acids occurs in the gastrointestinal tract
1) Gastrin (hormone secretes from stomach)
2) Pepsinogen → pepsin (hydrolyzes ingested
protein at peptide bonds)
3) Secretin secreted into blood which
stimulates the pancreas to secret
bicarbonate into small intestine.
4) Cholecystokinin (blood hormone) stimulate
Trypsinogen, chymotrypsinogen and
procarboxy-peptidase A and B.
5) Enteropeptidase (secrete by intestinal)
activated trypsinogen.
Acute pancreatitis ????
Pathways of amino acid degradation
The pathways of aa catabolism account
only 10%-15% of body energy.
From carbon skeleton of aa diverted to
gluconeogenesis or ketogenesis or
completely oxidized to CO2 and H2O.
The 20 catabolic pathways converge to
form only 6 major products, all of which
enter the citric acid cycle.
1- acetyl-CoA
2- pyruvate
3- oxaloacetate
4- fumarate
5- succinyl-CoA
6- α -ketoglutarate
Urea cycle
 Urea production occurs
almost exclusively in liver.
 Urea is produced from
ammonia in five
enzymatic steps.
(0)Carbamoyl phosphate
synthetase I.
1) Ornithine
transcarmoylase.
2) Argininosuccinate
synthetase.
3) Argininosuccinase.
4) arginase
Urea is produced from ammonia in 5
enzymatic steps
1)
Whatever the source, the NH+4 generated in liver mitochondria is used, together with
CO2 to form carbamoyl phosphate in matrix.
2)
Carbamoyl phosphate donates its carbamoyl group to ornithine to form citrulline.
This reaction catalyzed by ornithine transcarmoylase.
3)
The second amino group NH+3 enters from aspartate by condensation reaction
between amino group of aspartate and the ureido(carbonyl) group of citrulline
forming argininosuccinate. This reaction catalyzed by argininosuccinate synthetase .
4)
Argininosuccinate is then cleaved by argininosuccinase to free arginine and fumarate
which enters mitochondria to join the pool of citric acid cycle intermediates. This the
only reversible step in urea cycle.
5)
Arginine is now cleaved by argininase to yield urea and ornithine. Ornithine is
transported into mitochondrion to initiate another round of the urea cycle.
The citric
acid cycle
and urea
cycle can
be linked
 Fumarate produced in the argininosuccinase reaction is also an intermediate of the citric
acid cycle, the cycles are interconnected in process dubbed the “Krebs bicycle”.
 Each cycle can operate independently and connection between them depends on the
transport of the intermediates between the mitochondrion and cytosol.
 Aspartate formed in mitochondria by transamination between oxaloacetate and glutamate
can be transported to cytosol, where it serves as nitrogen donor in the urea cycle reaction
catalyzed by argininosuccinate synthetase. These reactions , making up the aspartateargininosuccinate shunt
Plasma proteins
• Plasma contains over 300 proteins.
• Many plasma proteins, including most enzymes
and tumor markers, have no known function in
blood, and arise as a result of cell death, tissue
damage or over expression by malignant cells.
• This table lists examples of commonly measured
plasma proteins that can be crudely assessed by
protein staining following separation using
electrophoresis (EPH).
When serum proteins are fractionated
0n cellulose acetate, 5 bands are
usually obtained at the end of the
electrophoretic run.
1) Albumin
2) α1-Globulins
3) α2-Globulins
4) β-Globulins
5) γ-Globulins
A) is normal serum proteins pattern.
B) Nephrotic syndrome.
C) Infectious hepatitis
D) hypogammaglobulinemia
E) Multiple myeloma
 Albumin (3.5-5.2g/dl) is quantitatively the most important contributor towards maintaining
the colloid oncotic pressure of plasma, and hypoalbuminaemia may lead to the development
of edema. Albumin also accounts for more than 50% of the total plasma protein
concentration.
 Increased albumin concentrations(hyperalbuminemia) are found in acute dehydration,
shock and if excessive venous stasis is applied during venipuncture.
hypoalbuminaemia
May arise from a number of conditions, including cirrhosis, nephrotic
syndrome, heart failure and malnutrition, however inflammation leading to
the acute phase response is the most common cause (Table 16.3).
A low albumin is an important prognostic indicator in hospitalized patients.
The immunoglobulins
 The immunoglobulins (Igs) are
synthesised by the plasma
cells of the lymphoreticular
system.
 There are five principal types
of heavy chain (γ,α, μ, δ and ε)
and two types of light chain (κ
and λ).
 Three major classes of Ig
(IgG, IgA and IgM) and two
minor ones (IgD and IgE) have
been recognised; the type of
heavy chain determines the
class. Table 16.4 lists several
features of the major classes.
• IgG immunoglobulins are the major antibody of the secondary immune response and are
formed particularly in response to soluble antigens such as toxins and the products of bacterial
lysis. They are widely distributed, and cross the foetoplacental barrier.
• IgM immunoglobulins are pentamers of the basic Ig structure linked around a J chain
polypeptide. They tend to be formed especially in response to particulate antigens, such as
those on the surface of bacteria. In the presence of complement, IgMs are very effective in
producing lysis of these cells.
• IgA immunoglobulins in plasma, are monomers. however, over 50% of IgA
synthesis occurs in lymphoreticular cells under the mucosa of the respiratory and
alimentary tracts. Here dimeric ‘secretory IgA’ is synthesised and secreted into the
alimentary or respiratory tract giving defence against local infections.
• IgD immunoglobulins are present in minute amounts in plasma with
monomer IgM, on the surface of B lymphocytes. They are probably concerned
with antigen recognition and with the development of tolerance.
• IgE immunoglobulins bind to cells such as the mast cells of the nasopharynx.
In the presence of antigen (allergen), an antigen–antibody reaction leads to the
release of histamine and other amines and polypeptides from the mast cell,
giving rise to a local hypersensitivity reaction.
The concentrations of IgM and IgA in serum are low at birth and
gradually rise until adult levels are achieved at approximately 1 year
and 10 years, respectively.
In contrast, IgG is high at birth due to transplacental passage of
maternal IgG. After birth IgG falls due to loss of maternal IgG but then
gradually rises again until adult values are found after 1 year.
 The total serum protein concentration in adult varies from 6.0 to 8.2g/dl.
 The total protein concentration is lower in newborn but slowly reaches the
adult level in a bout 1 year or so.
Serum total proteins
6.0-8.2g/dl
Increased concentration
 Dehydration
 Monoclonal disease
(multiple myeloma,
macroglobulinemia,
cryoglobulinemia)
 In some chronic polyclonal
disease (liver cirrhosis,
sarcoidosis, systemic lupus
erythematosus, and chronic
infection).
Abnormal , monoclonal
protein is called a paraprotein.
Decreased concentration







overhydation
Nephrotic syndrome
Skin burns
Protein-losing enteropathies
Starvation
Protein malnutrition
Sever nonviral liver cell
damage.
1) α1-Globulins: increased in infections and inflammatory disease. It is decreased in
acute hepatitis and in familial α1-antitrypsin deficiency, which is a cause of
pulmonary emphysema.
2) α2-Globulins: increased in nephrotic syndrome, inflammatory condition
(rheumatoid arthritis or after MI). Decreased in acute hepatocellular disease.
3) β-Globulins: is usually increased in hyperlipemias of various types.
4) γ-Globulins: Hodgkin's disease, a malignant disease involving the lymph nods, in
the early stages its concentration may be moderately increased.
Cerebrospinal fluid (CSF) protein
 CSF is normally clear and colourless. Turbidity is usually due
to leucocytes, but it may be due to microorganisms.
 Blood-stained CSF may indicate recent haemorrhage, or
damage to a blood vessel
during specimen collection.
 Xanthochromia (yellow colour) is most often due to previous
haemorrhage into the CSF, but it may indicate that CSF
[protein] is very high.
 The CSF may be yellow in jaundiced patients.
Electrophoresis of concentrated CSF . Normal CSF total protein = 30 mg/dl.
CSF total protein
15-45mg/dl
Increased concentration






In various types of meningitis.
Neurosyphilis.
In some cases of encephalitis.
In some brain tumors.
Abscesses.
Frequently after cerebral
hemorrhage.
Decreased concentration
 Has no clinical significance.
Urine protein
a normal urine may contain 0.05-0.1g/24 hours period, even though this may not be detected
by routine methods.
Increased excretion
Protein may be lost in large quantities in nephrotic syndrome in
which the lesion is in the basement membrane of the glomerulus;
lesser amounts of protein are excreted in other disease producing
renal lesion.
Bence-Jones protein, the light chains of immunoglobulins, appears in
urine in may cases of myelomatosis.
The amount excreted depends to large extent upon the stage and
severity of the disease.
The Bence-Jones protein , predominates in the sample
as gamma globulin.
Bence-Jones protein
 Bence-Jones protein is a protein with peculiar thermal
solubility properties.
 It is found in the urine of about 50% of the patients with
multiple myeloma.
 The protein is polypeptide consisting of a light chain type.
 The heat test for Bence-Jones protein, which depends on a
protein precipitating when urine is heated to 40-60 C, but which
dissolves when heating is continued beyond 80 C