Lipoproteins Flashcards
Chylomicron
formed in the intestines
Main lipid: TAG
Apoproteins: B-48 (A,C,E)
it transports dietary TAG to adipose and other tissues
Chylomicron remnant
main lipid: TAG
Apoproteins: B-48 (A,C,E)
delivers remaining dietary TAG to the liver. exchanged TAG for cholesterol ester from HDL; delivers CE to the liver
VLDL
formed in the liver
main lipid: TAG
apoprotein: B-100 (A,C,E)
transports endogenously synthesized TAG to adipose tissue, skeletal and heart muscle. Exchanges TAG for CE from HDL
IDL
VLDL remnant formed in liver
main lipid: TAG and cholesterol
Apoprotein: B-100, E
Delivers remaining TAG and cholesterol to the liver. exchanges TAG for CE from HDL. Delivers CE to the liver
LDL
formed via processing of IDL in the circulation
Main lipid: cholesterol
Apoprotein: B-100
Delivers cholesterol to the liver and other cells, including steroidogenic cells
HDL
formed in the liver, and sometimes in th intestines
main lipid: cholesterol
Apoprotein: A’s (C, E)
Accepts cholesterol from peripheral cells, esterifies it, and transports CE’s to the liver. Exchanged CE for TAG in VLDL, IDL, chylomicron remnants
Atheroprotective via enzymes such as paraoxonase that inhibit LDL oxidation. Serves as a resovoir for circulating apoproteins (A,C,E) which are transported to other lipoprotein particles.
B-48
Majot LP: Chylomicron
function: chylomicron secretion
B-100
Major LP: VLDL, IDL, LDL
function: Binds LDL recepto, VLDL secretion
A-1
Major LP: HDL
function: activates LCAT (lecithin: cholesterol acyl transferase) and binds HDL receptor
C-II
Major LP: CyM, IDK, VLDL, HDL
function: cofactor that activates LP lipase
E
Major LP: CyM, VLDL, IDL
Function: Cleaance via binding to LRP (LDL receptor associated protein)
Which Apo proteins are cofactors for enzymes?
Apo-CII: lipoprotein lipase
Apo-AI: lecithin: cholesterol acyltransferase
Which apolipoproteins are ligands for extracellular receptors?
ApoE: Binds to LRP
Apo: B-100: Binds to LDL receptor
Apo A-I: binds to HDL receptor
Structural proteins in a lipoprotein particle
Apo B-48: Chylomicrons
Apo B-100: VLDL, IDL, LDL
Apo A-I: HDL
Chylomicron metabolism
1) chylomicrons transport dietary TAG and cholesterol
2) Nascent chylomicrons are synthesized in the intestines along with Apo A-1 and Apo B-48. transported in lymph.
3) Chylomicrons transiently gain ApoE and Apo C-II from HDL in the plasma
4) Apo protein C-II activates lipoprotein lipase (LPL), located on capillary endothelia. LPL catalyzes the conversion of TAGs to free fatty acids an glycerol. Fatty acids are taken up by tissues and metabolized.
5) Chylomicron remnants are removed and destroyed by the liver via receptor mediated endocytosis. This involved ApoE which binds to the LDL receptor and LDL related protein.
6) HDL serves as a repository for Apo C-II, A-I, and E