Alpha antitrypsin

MANEESHA M JOSEPH
MSC MLT MICROBIOLOGY

PLASMA PROTEINS
 Plasma contains a large variety of proteins including albumin, immunoglobulins, and clotting
proteins such as fibrinogen. Albumin constitutes about 60% of the total protein in plasma and is
present at concentrations between 3.5 and 5.5 g/dL.
 It is the main contributor to osmotic pressure of the blood and it functions as a carrier molecule
for molecules with low water solubility such as lipid soluble hormones, enzymes, fatty acids,
metal ions, and pharmaceutical compounds.
 2 – 3.5 g/dL are serum globulins (transport protein, reactants of acute phase,immunoglobulins)

GENERAL PROPERTIES OF PLASMA PROTEINS
Most are synthesized in the liver
• Exception: -globulins – synthesized in plasma cells
Synthesized as pre-proteins on membrane-bound polyribosomes; then they are subjected to post
translational modifications in ER and Golgi apparatus
Almost all of them are glycoproteins
• Exception: albumin
They have characteristic half-life in the circulation (albumin – 20 days)
Many of them exhibit polymorphism (immunoglobulins, transferrin)
Degradation:
• hepatocytes, mononuclear phagocytic system (complexes of antigen-antibody)

TYPES OF PLASMA PROTEINS
1. Albumin
2. Globulins
a-globulins : a1 , a2-globulins
b-globulins: b1 ,b2-globulins
g-globulins
3. Fibrinogen
Under different pathological conditions the protein levels depart from the normal range.

TYPES OF PLASMA PROTEINS
Electrophoresis of plasma proteins
+ -
albumin
a1 a2
-globulins

THE MAIN COMPONENT OF THE GLOBULINS
a1-AT
Haptoglobin
a2--macroglobulin
HDL
Transferrin
LDL, C3
Immunolobulins
Fibrinogen, CRP
a1 a2albumin b1 b2 

ELECTROPHORESIS FRACTIONS OF PLASMA PROTEINS
Fraction Rel. amount (%) c (g/l)
Albumins: albumin
pre-albumin (transthyretin)
52 – 58 34 – 50
a1-globulins: thyroxin-binding globulin, transcortin,
a1-acid glycoprotein, a1-antitrypsin, a1-lipoprotein (HDL),
a1-fetoprotein
2.4 – 4.4 2-4
a2-globulins: haptoglobin, macroglobulin, ceruloplasmin 6.1 – 10.1 5 – 9
b-globulins: transferrin, hemopexin, lipoprotein (LDL),
fibrinogen, C-reactive protein, C3 and C4 components of the
complement system
8.5 – 14.5 6 – 11
-globulins: IgG, IgM, IgA, IgD, IgE 10 – 21 8 – 15

FUNCTIONS OF PLASMA PROTEINS
Transport of substances :
albumin – fatty acids, bilirubin, calcium, drugs
transferin – iron
cerulplasmin – copper
transcortin – cortisol, cortikosteron
lipoproteins – lipids
haptoglobin – free hemoglobin
thyroxin binding globulin – thyroxin
retinol binding protein - retinol
Osmotic regulation:
 Plasma proteins are colloidal and non-diffusable and exert a colloidal osmotic pressure
which helps to maintain a normal blood volume and a normal water content in the
interstitial fluid and the tissues.
 Decrease in albumin level results in loss of water from blood and its entry into
interstitial fluids causing edema.

Catalytic function (enzymes)
e.g lipases for removal of lipids from the blood
Protective function:
 Immunoglobulins combine with foreign antigens and remove them.
 Complement system removes cellular antigens.
 Enzyme inhibitors remove enzymes by forming complexes with them. e.g. a1-antitrypsin
combines with elastase, trypsin and protects the hydrolytic damage of tissues such as
lungs.
 Some proteins increase during acute phase and protect the body. E.g. a1-antitrypsin, a2-
macroglobulins

Blood clotting:
 Many factors are involved in clotting mechanism and prevent loss of
excessive amount of blood; e.g. clotting factors IX, VIII, thrombin,
fibrinogen etc.
 An excess of deficiency leads to a disease; e.g. hemophilia, thrombus
formation
Anticoagulant activity (thrombolysis):
Plasmin breaks down thrombin and dissolves the clot
Buffering capacity:
Proteins in plasma help to maintain acid-base balance

TYPES OF APRs:
Positive:
C-reactive protein:
~1000-fold increase!
a1-antitrypsin
fibrinogen
haptoglobin (HP)
C3, C4
serum amyloid A
(SAA)
Negative:
albumin
transferrin
antithrombin
transcortin
retinol binding
protein

THE IMPORTANCE OF POSITIVE ACUTE PHASE REACTANTS
Components of the immune response
C-reactive protein, complement components (C3 a C4),TNF-a, Il-1, Il-6
Protection against collateral tissue damage
scavergers of ROS and protein stabilizing transition metals and their complexes
haptoglobin
hemopexin
feritin
Ceruloplasmin
Inhibitors of proteases
a1-antitrypsin
a1-antichymotrypsin
a2-macroglobulin

Transport of waste products produced during inflammation :
hemoglobin
hemopexin
serum amyloid A (SAA)
Coagulation factors and proteins involved in tissue regeneration :
fibrinogen
prothrombin
factor VIII
von Willebran factor
plasminogen
The criterion for determining inflammation (decrease inflammation)
Transkortin (cortikoid binding protein)
The criterion for protein synthesis in the liver

ALPHA I ANTITRYPSIN
 Described by Schultz in 1995 later giving this name because of its inhibition of trypsin
 The name “a1-proteinase inhibitor” was introduced later bcause of AAT’s
broad spectrum of inhibition of Serine proteases (not only trypsin)
 a1-antitrypsin,is a glyco protein mainly synthesised in liver,also called serpins.
 Single poly peptide chain having 394 amino acids
 Molecular weight approximately 52kda
 Normal value in adults 2 to 4 gm/Dl
 It inhibits trypsin,elastase and certain proteases by forming complexes with them

 Most important function is the inhibition of protease neutrophil elastase
 Neutophil elastase is released from leukocytes to fight infection,but it can destroy alveoli
which can lead to emphysema if not controlled by AAT
 Mutations in SERPINA I gene cause deficiency of AAT protein or abnormal form of
protein that cant control neutrophil elastase. Abnormal form of AAT accumulate in liver
and cause cirrhosis

PHENOTYPES
 Several phenotypes of a1-antitrypsin have been identified.
 The most common phenotype is MM (allele PiM) associated with normal antitrypsin activity
 Other alleles are PiS, PiZ, PiF, Pi- (null).
 The homozygous phenotype ZZ suffers from severe deficiency of a1-antitrypsin and susceptible
to lung disease( emphysema) and cirrhosis of liver
 Individuals with MZ OR MS phenotype are usually not affected but they can have offspring
who may be ZZ,Z- and be in danger.

INCREASE OF SERUM a1-ANTITRYPSIN
1.In response to inflammation-acute,sub acute and chronic .It is considered as one of the
“acute phase reactant “and increased in trauma,burns,infarction,malignancy,liver
disease,etc
2.Chronic hepatocellular disease and biliary obstruction – either normal or increased
3.In pregnancy and also during contraceptive medication
4.Neonates have serum concentrations much below adult values,but show gradual
increase with age and achievement of adult levels is rapid

DECREASE IN SERUM a1-ANTITRYPSIN
1.In protein losing disorder
i)Nephrotic syndrome
ii)Diffuse hypoproteinaemias
2. In emphysema of lungs
3.Juvenile cirrhosis liver
CLINICAL SIGNIFICANCE
1. Role in Emphysema Lung
 A deficiency of a1-antitrypsin has a role in certain cases,approximately 5% of emphysema
of lung.
 This occurs mainly with ZZ phenotype who synthesise PiZ

Biochemical mechanism
Normally a1-AT protects lung tissue from injurious effects by binding with the proteases,viz
“active elastases”.A particular methionine is involved in binding with the protease
Thus;
Active elastase + a1-AT
Inactive elastase: a1-AT complex
No proteolysis of lung No tissue damage
When a1-AT is deficient or absent the above complex with active elastase does not take place and
active elastase brings about proteolysis of lung and tissue damage.
Active elastase +No or decreased a1-AT
Active elastase Proteolysis of lung
(complex does not form)
Tissue damage

2. Relation of smoking with emphysema
Smoking oxidises the methionine of a1-AT and thus inactivates the protein ,hence such a1-AT
cant bind to protease ‘active elastase’ and thus proteolysis of lung and tissue damage occurs accelerating
the development of emphysema.
3.Role in cirrhosis
Juvenile hepatic cirrhosis has also been correlated with a1-AT deficiency
In this condition molecules of Pi Z accumulate in the cisternae of the endoplasmic reticulum of
hepatocytes.The hepatocytes can not synthesise this particular type of a1-AT .Thus PiZ protein of a1-AT is
synthesised but not released from the hepatocytes.This results in cirrhosis of liver
4. Role as tumor marker
It is increased in germ cell tumors of testes and ovary
5.As an inhibitor of Fibrinolysis
a1-AT is one of the most important inhibitors to fibrinolysis along with a2-Antiplasmin and a2-
macroglobulin. All these inhibitors block action of plasmin on fibrinogen

ANALYTICAL METHODS
 It is the major constituent of the a1-globulin band on routine serum electrophoresis. The
other a1-globulins, AAG and a1-lipoprotein do not stain with peptide stains because their
high content of CHO & lipid
 Analytical methods used to determine a1-antitrypsin are radial immunodiffusion,
“rocket “electrophoresis and immuno nephelometric methods,immuno turbidimetry.
 For screening of phenotypes-Immunofixation method has been used

ALPHA-FETOPROTEIN
 AFP, α-fetoprotein; also sometimes called alpha-1-fetoprotein, alpha-fetoglobulin,
or alpha fetal protein is a protein that in humans is encoded by the AFP gene .
 The AFP gene is located on the q arm of chromosome 4
 Alpha-fetoprotein (AFP) is a single chain glycoprotein with a molecular weight of
approximately 70,000 daltons and alpha electrophoretic mobility.
 AFP was first identified in 1956 by Bergstrand and Czar in human fetal serum as an
embryo specific protein.
 AFP is a major plasma protein produced by the yolk sac and the liver during fetal
development. It is thought to be the fetal form of serum albumin. By the second year of
life and thereafter only trace amounts are normally detected in serum.

 The reappearance of elevated AFP concentrations in adult serum has been observed not
only during pregnancy, but also in conjunction with several benign and malignant
diseases. i.e. it is a carcinoembryonic protein (or oncofetal antigen)
 AFP binds to copper, nickel, fatty acids and bilirubinand is found
in monomeric, dimeric and trimeric forms.
 AFP of fetal serum origin is cleared by the fetal kidneys and excreted by urination into
amniotic fluid.
 Amniotic fluid AFP (AF-AFP) levels increase with each week of gestation and peak at
about 13-14 weeks at a level of approximately 15-20 µg/ml, after which the levels
rapidly decline until about 22 weeks gestation and then gradually decline.
 AFP is also used as a tumor marker for classification and monitoring therapy for
nonseminomatous testicular cancer in combination with another tumor marker:
b-human chorionic gonadotropin (b- hCG)

ELEVATED ALPHA-FETOPROTEIN
AFP is measured in pregnant women through the analysis of maternal blood or amniotic
fluid , as a screening test for a subset of developmental abnormalities. Some of the
diseases in which AFP will be elevated in a person are listed below:
 Omphalocele
 Hepatocellular carcinoma/hepatoma: ↑ α-fetoprotein
 Neural tube defects: ↑ α-fetoprotein in amniotic fluid and maternal serum
 Nonseminomatous germ cell tumors
 Yolk sac tumor
 Ataxia telangiectasia: Elevation of AFP is used as one factor in the diagnosis
of ataxia telangiectasia
 Tumors: AFP can also be used as a biomarker to detect a subset of tumors in non-
pregnant women, men, and children. A level above 500 nanograms/milliliter of AFP
in adults can be indicative of hepatocellular carcinoma, germ cell tumors,

REFERENCES
 Text book clinical biochemistry and molecular diagnosis-Tietz
 Text book of biochemistry-Styrer
 Text book of biochemistry-Voet
 Text book of biochemistry-Lehninger
 Text book of biochemistry-Devlin
 Harper’s illustration biochemistry
 Michael Bishop clinical chemistry

Alpha antitrypsin

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Alpha antitrypsin