Lipoproteins

Question 1

What are the types of Apoproteins?

Answer 1

Apo A (I, II, IV)
Apo B (-48, -100)
Apo C(I, II, III)
Apo D
Apo E (II, III, IV)
Apo (a)
Apo M

Question 2

What are the main enzymes of plasma lipoprotein metabolism? Other associated proteins of metabolism?

Answer 2

Enzymes:
Lipoprotein Lipase
Hepatic Lipase
Lecithin: Cholesterol acyltransferase (LCAT)
ATP Binding Cassette transporters 

Other:
Cholesteryl Ester Transfer protein
Phospholipid Transfer Protein

Question 3

Where is LPL found? What doe sit interact with? What does it do?

Answer 3

• Adipose and striated muscle
• Interacts with chylomicrons and VLDL via Apo C-11
• Converts triglycerides to 2 free fatty acids and glycerol

Question 4

Where is Hepatic Lipase? What does it do?

Answer 4

• Liver, Plasma, and macrophages

- Triglycerides —> 2-monoglycerol + 2 free fatty acids

Question 5

What is the role of lecithin (LCAT)? Where is it located? How is it activated?

Answer 5

• Made in liver; activated by Apo 1A

- Convers cholesterol to cholesteryl Ester

Question 6

What is the role of cholesteryl ester transfer protein (CTEP)?

Answer 6

AIDS in the conversion of HDL to LDL & VLDLs

Question 7

Where is ABCA1 located? What is it’s role?

Answer 7

• In macrophages (esp foam cells), brain, liver, adrenal, etc.
• Cell membrane Transporter which mediates transport of cholesterol. Phospholipids, and other metabolites from cells to lipid depleted HDL apolipoproteins.
• Rate limiting step for formation of HDL

Question 8

What are the major lipoproteins for HDLs?

Answer 8

A-I

E

Question 9

What is the role of HDL?

Answer 9

• After synthesis in liver, circulates in blood to acquires cholesterol from peripheral tissue via ABCs
• Acts as revervoir for Apo C-II and E; donates them to VLDL/chylomircrons in circulation
• As HDL acquires more CEs, it is transformed to HDL 2 in which is interacts with SRB1 receptor in liver which facilitates removal of CEs and returns HDL to circulation

Question 10

How can HDL be internalized?

Answer 10

Apo E is recognized by LDL and therefore HDL may be internalized via that route

Question 11

What factors concerning HDLs may contribute to reverse cholesterol transport?

Answer 11

• Concentration

- “Quality” of HDL

Question 12

How are HDL transported out of the membrane of a vessel wall Macrophage?

Answer 12

• Passive Diffusion (FC-Pl)
• SR-BI Pathway
• ABCA1 pathway

Question 13

Which apolipoprotein associates with HDLs what have high concentrations of Sphingosine-1-phosphate?

Answer 13

Apo M

Question 14

What is the role of chylomicrons?

Answer 14

Carry dietary fat from the gut to venous circulation.

Question 15

What is the fate of remnant chylomicrons after loss of dietary fats?

Answer 15

Taken up by the liver to be incorporated into VLDLs

Question 16

What Apo’s are associated with VLDLs?

Answer 16

B-100
C-11
C

Question 17

What is the role of VLDLs?

Answer 17

Carry Fatty acids and cholesterol to adipose and muscle via action of LPL

Question 18

What are IDL and LDL?

Answer 18

• Smaller, more dense derivative of VLDL.

- Apo B-100 and E

Question 19

What is the shared role of VLDL, LDL, and IDL?

Answer 19

Carries Tags/cholesterol to peripheral tissues from liver

Question 20

What is Lp(a)?

Answer 20

A variant of LDL w/ additional protein apo(a) linked via sulfhydryl bond to Apo B-100.

*Lp(a) is an independent risk factor for atherosclerosis

** Apo(a) shown to interfere with fibrinolysis