section 20.1
Structure and Composition
431
TABLE 20-1
Properties of Human Apolipoproteins*
Apolipoprotein
Plasma
Concentration
(mg/dL)
(approximate)
Molecular
Weight
Major Density
Class
Biological Function in
Addition to Structural
and Transport Role
A-I
100-150
29,016
HDL
Activates LCAT, cell-receptor
binding (?)
A-II
30-50
17,414
HDL
Inhibits LCAT (?) enhances
hepatic lipase activity.
A-IV
15
44,465
Chylomicron
Unknown.
B-100
80-100
512,723
VLDL, LDL
Necessary for triacylgycerol
secretion; binding to cell
receptors.
B-48
<5
241,000
Chylomicron
C-I
7
6630
Chylomicron, VLDL
Cofactor with LCAT.
C-II
4
8900
Chylomicron, VLDL
Activates LPL.
C-III
1 2
8800
Chylomicron, VLDL
Regulates LPL reaction;
inhibits uptake of remnants
via apo E receptor.
D
6
19,000
HDL
LCAT reaction, cholesteryl
ester transfer.
^2-4
3-7
34,145
VLDL, IDL, HDL
Binding to specific receptors
(a)
1 0
300,000-800,000
LDL, HDL
Competes with plasminogen
for its receptors and may
inhibit thrombolysis.
*LCAT=Lecithin-cholesterolacyltranferase;LPL=lipoprotein lipase; VLDL=very-low-density lipoprotein; LDL=low-density lipoprotein; HDL=
high-density lipotrotein; IDL=intermediate density lipoprotein.
centrifuged at 100,000 x
g
overnight, and the LDL frac-
tion is removed from the top. The density of the remaining
material is raised to 1.21. After centrifugation for 2 days
at 100,000 x
g,
the HDL fraction is obtained from the top.
In electrophoresis of plasma or serum at alkaline pH,
with either paper or agarose as a support medium, the
lipoproteins migrate to different positions. The lipopro-
tein bands are identified by staining with appropriate lipid
TABLE 20-2
Physical Data for the Major Types of Lipoprotein
Lipoprotein
Hydrated Density
(g/ml)
Sf*
Position of Migration in Paper or Agarose
Electrophoresis in Comparison with Serum Globulins
Chylomicrons
<0.95
>400
Origin
VLDL
0.95-1.006
20-400
a 2-(migrates ahead of /3-globulin to pre-/3 position)
LDL
1.006-1.063
0 - 2 0
/3 (with /3-globulin)
h d l
2
1.063-1.125
—
«j (with ctj -globulin)
HDL
3
1.125-1.210
—
Lp(a)
1.040-1.090
—
Slow pre-/3-LP
*The rate at which lipoprotein floats up through a solution of NaCl of specific gravity 1.063 is expressed in Svedberg flotation units or Sf; one Sf
unit= 10-13 cm/sec/dyne/g at 26°C. Sf can be thought of as a negative sedimentation constant.
