2. Lipoproteins Function: Transport of fat soluble substances
Types: 1) Chylomicron
2) VLDL
3) LDL
4) HDL

3. Triacylglycerol % of dry wt
Lipoprotein class
Density (g/mL)
Diameter (nm)
Protein % of dry wt
Phospholipid %
Triacylglycerol % of dry wt
HDL
5 – 15 33 29 8
LDL
1.019 – 1.063
18 – 28 25 21 4
IDL 18 22 31
VLDL
0.95 – 1.006 10 50
chylomicrons
< 0.95
1 - 2 7 84

4. Apolipoproteins: specific lipid-binding proteins that attach to the surface
intracellular recognition for exocytosis of the nascent particle after synthesis
activation of lipid-processing enzymes in the bloodstream,
binding to cell surface receptors for endocytosis and clearance.
Main lipid components: triacylglycerols, cholesterol esters, phospholipids.
Major lipoproteins:
chylomicrons
very low density lipoproteins (VLDL)
low density lipoproteins (LDL)
high density lipoproteins (HDL)
Subfraction: intermediate density lipoproteins (IDL)
Electrophoretic mobility (charge):
HDLs =  lipoproteins
LDLs = -lipoproteins
VLDLs = pre- lipoproteins (intermediate between  and  mobility).

11. chylomicron interacts with lipoprotein lipase removing FFA
Lymph system:
Chylomicrons to capillaries via lymph
INTEST
INE
Nascent chylo-microns acquire apo CII (C) and E (E) from HDL
non-hepatic tissues
C E
C E
C E
C E
ApoB48 aids with chylo-micron assembly
LIVER
Figure 3. Exogenous pathway of lipid transport.
Chylomicrons carry dietary fatty acids to tissues
and the remnants take cholesterol to the liver

12. Triacylglycerol
in core
Chylomicron (or VLDL)
To Liver
Apo CII
LIPOPROTEIN LIPASE
Glycerol
Free fatty acids
Polysaccharide
Chain
Endothelial
Surface of cell
Capillary
In cellulo (muscle & adipose)
Free fatty acids
Figure 4. Lipoprotein lipase action on chylomicron triacylglycerol (an identical reaction occurs with VLDL)

13. chylomicron interacts with lipoprotein lipase removing FFA
Lymph system:
INTEST
INE
C E
chylomicron acquires apo CII (C) and E (E) from HDL
non-hepatic tissues
C E
C E C E
chylomicron remnants lose CII to HDL C E
ApoB48 E
Liver: apo E receptor takes up remnants to deliver cholesterol
LIVER
Figure 3. Exogenous pathway of lipid transport. Chylomicrons carry dietary fatty acids to tissues and the remnants take cholesterol to the liver

14. nascent VLDL acquires apo CII (C) and apo E (E) from HDL
LPL hydrolyze TAGs; FFA uptake; LDL circulate to tissues
B100 (B) helps assemble and export nascent VLDL
non-hepatic tissues
LIVER
C E
C E B
C E
C E
C E
bile acids B
CII and E release to HDL
Cholesterol uptake; excreted as bile acids
apo B100 on LDL bind to receptor B B
LDL taken into the cell to deliver cholesterol
Apo E binds liver receptor
HDL scavenge cholesterol
Figure 5. The liver-directed endogenous pathway of lipoprotein metabolism.

15. Fig. 6 Chylomicron Processing and Interface with HDL
Chylomicrons:
Exogenous Pathway
Fig. 6 Chylomicron Processing and Interface with HDL
HDL: Both Pathways
Nascent Chylomicron
Assembly in Gut
Mediated by B48
B48
Nascent HDL
Assembled in liver
Loans apo E/ apo CII to nascent chylomicrons E
CII A1
apo E & CII
from HDL E E
B48 E
CII E
CII
Mature Chylomicron
Apo E and CII added from HDL
CII activates LPL
Mature Chylomicron
Apo E and CII added from HDL
Lipoprotein Lipase
capillary walls
hydrolyzes TAG
deliver FFA into adipose/muscle
B48 E
CII
CII
CII
adipose &
muscle
FFA
Mature HDL
CE from peripheral cells via LCAT activated by apo A1
Apo CII returned by chylomicrons
apo CII A1
Chylomicron Remnant
from mature chylomicron
apo CII returned to HDL
CII
CII
CII E
B48
Triacylglycerol
Cholesterol ester
Phospholipid

16. Figure 7. Cellular cholesterol uptake, metabolism and release.
sorting endosome: ligand/receptor dissociation
LDL receptor
transport vesicle- lysosome fuse forming late endosome
Recycling of receptor and clathrin
Recycling of receptor
lysosome
ooo
clathrin-
coated pit
Golgi
late endosome
NPC-1 mediated transfer
ooo
free pool of
cholesterol
ACEH
CE  cholesterol
B100  amino acids
ACAT (stimulated by cholesterol)
Cholesterol release for transport to liver
endocytosis
Cholesterol Esterase
CE stored in droplets
vesicle CE CE
LDL CE
CERP
Cholesterol metabolism to bile acids or steroids
Membrane
Cholesterol
Apo A1 receptor L CA T A1 E
CII
CE in nascent HDL
Apo A1 binds to receptor, activates CERP to pump out cholesterol, and LCAT to esterify cholesterol A1
CII E
Reverse
Cholesterol
Transport
Figure 7. Cellular cholesterol uptake, metabolism and release.
Mature HDL:
Cleared by liver