Plasma proteins are:
1. Serum albumin
2. Serum globulin
3. Fibrinogen.
Serum contains only albumin and globulin.
Fibrinogen is absent in serum because, it is converted into fibrin
during blood clotting. Because of this, the albumin and globulin are usually
called serum
albumin and serum globulin.
NORMAL VALUES
Normal values of the
plasma proteins are:
Total proteins : 7.3 g/dL (6.4 to 8.3
g/dL)
Serum albumin : 4.7 g/dL
Serum globulin : 2.3 g/dL
Fibrinogen : 0.3 g/dL
ALBUMIN/GLOBULIN
RATIO
Ratio between plasma level
of albumin and globulin is called albumin/globulin (A/G) ratio.
It is an important
indicator of some diseases involving liver or kidney.
Normal A/G ratio is 2 : 1.
SEPARATION OF PLASMA PROTEINS
Plasma proteins are
separated by the following methods.
1. PRECIPITATION
METHOD
Proteins in the serum are separated
into albumin and globulin. This is done by precipitating globulin with 22% sodium
sulfate solution. Albumin remains in solution.
2. SALTING-OUT METHOD
Serum globulin is separated
into two fractions called euglobulin and pseudoglobulin by
salting out with different solutions. Euglobulin is salted out by full
saturation with sodium chloride solution; half saturation with magnesium sulfate
solution and onethird saturation with ammonium sulfate solution. It is
insoluble in water. Pseudoglobulin is salted out by full saturation with magnesium
sulfate and, half saturation with ammonium sulfate. It is soluble in water but
it cannot be salted out by
sodium chloride solution.
3. ELECTROPHORETIC
METHOD
In this, the plasma proteins are
separated depending on their differences in electrical charge and the
rate of migration.
It is done in a Tiselius
apparatus by
using paper or cellulose or starch block. By this method, the proteins are
separated into albumin (55%), alpha globulin (13%), beta globulin (14%), gamma
globulin (11%) and fibrinogen (7%).
4. COHN’S FRACTIONAL
PRECIPITATION METHOD
By this method, plasma
proteins are separated into albumin and different fractions of globulin,
depending
upon their solubility.
5.
ULTRACENTRIFUGATION METHOD
In this method,
albumin, globulin and fibrinogen are separated depending upon their density. This
method is also useful in determining the molecular weight of these proteins.
6. GEL FILTRATION
CHROMATOGRAPHY
Gel filtration
chromatography is a column chromatographic method by which the proteins are
separated on the basis of size. Protein molecules are separated by
passing through
a bed of porous beads. The diffusion of different proteins into the beads
depends upon their size.
7.
IMMUNOELECTROPHORETIC METHOD
By this method, the
proteins are separated on the basis of electrophoretic patterns formed by
precipitation at the site of antigenantibody reactions. This technique provides
valuable quantitative measurement of different proteins.
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