Page 137 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM SECTION II 93

Key enzymes in lipid
transport
Cholesteryl ester Mediates transfer of cholesteryl esters to other lipoprotein particles.
transfer protein
Hepatic lipase Degrades TGs remaining in IDL.
Hormone-sensitive Degrades TGs stored in adipocytes.
lipase
Lecithin-cholesterol Catalyzes esterification of ⁄3 of plasma cholesterol.
2
acyltransferase
Lipoprotein lipase Degrades TGs in circulating chylomicrons.
Pancreatic lipase Degrades dietary TGs in small intestine.
PCSK9 Degrades LDL receptor   serum LDL. Inhibition   LDL receptor recycling   serum LDL.

Liver

Transfer of
Nascent LCAT Mature CETP cholesteryl
esters to
HDL HDL
VLDL, IDL,
LDL

Small intestine

Major apolipoproteins
Chylomicron
Apolipoprotein Function Chylomicron remnant VLDL IDL LDL HDL
E Mediates remnant uptake ✓ ✓ ✓ ✓ ✓
(everything except LDL)

A-I Found only on alpha- ✓
lipoproteins (HDL), activates
LCAT
C-II Lipoprotein lipase cofactor that ✓ ✓ ✓ ✓
catalyzes cleavage.
B-48 Mediates chylomicron ✓ ✓
secretion into lymphatics
Only on particles originating
from the intestines
B-100 Binds LDL receptor ✓ ✓ ✓
Only on particles originating
from the liver

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