Lipoprotein

Structure and Composition of LDL
LDL is a spherical particle and in normal individuals ranges 20.0 to 23.0 nm in diameter. The average molecular weight is 2.310⁶. Compared with other lipoproteins, LDL particles are relatively homogeneous in size and composition, however, LDL particles can be separated into several subfractions of increasing density and decreasing size. LDL consists of protein (20-25%), phospolipid (20-25%), free cholesterol (6-10% ), cholesterol ester (35-45%) and triglyceride (6-12%). Apo B-100 is the sole constituent apolipoprotein on LDL. It is presumed that the cholesteryl esters and triglycerides form the hydrophobic core, which is surrounded by a surface coat of apolipoprotein B, free cholesterol and polar phospholipid components oriented toward the aqueous medium.
[Table 2001] (Ref. 1001/1002/1003/1004/1005/1006/1007/1015/1207)

Composition and Structure of HDL
The average molecular weight of HDL₂ is 3.610⁵ and consists of protein (35-40%), phospholipid (30-40%), free cholesterol (4-6%), cholesteryl ester (15-20%) and triglyceride (3-6%). The average molecular weight of HDL₃ is 1.7510⁵ and consists of protein (45-55%),phospholipid (25-35%), free cholesterol (1-3%), cholesteryl ester (8-15%) and triglyceride (3-6%). The ratio of phosphatidyl choline to sphingomyelin and that of free to estetified cholesterol is greater for HDL2 than for HDL3.Approximately 90% of the constituent apolipoproteins on HDL2 and HDL3 are apolipoprotein A-I (apo A-I) and apolipoprotein A-II (apoA-II) .Apolipoprotein C (apo C),apo E and apolipoprotein A-IV (apo A-IV) are found in small quantities. The relative proportion of apoA-I and apo A-II varies in the HDL subfractions .
Preparation by zonal ultracentrifugation shows an apo A-I/apo A-II molar ratio of 9:1 in the HDL₂ fraction and 2:1 in the HDL₃ fraction.
HDL particles are secreted as discoidal particles or small spherical particles. Discoidal HDL consists of phospholipid and some unesterified cholesterol organized as a lipid bilayer associated with apo A-I.The discoidal particles are designated nascent HDL, and are transformed into spherical particles by lecithin:cholesterol acyl transferase (LCAT) reaction.In all of the sub fractions , HDL exists as spherical particles which contain the same chemical constituents,but differ in particle size, density and stoichiometry.The structure of HDL is presumed to comprise cholesteryl esters and triglycerides in the hydrophobic core, surrounded by a surface coat of apo A-I,apo A-II ,phosphatidyl choline and sphingomyelin oriented toward the aqueous medium.
[Table 2001] (Ref. 1001/1003/1005/1006/1206/1207)

Structure of VLDL
VLDL is spherical particle and in normal individuals ranges 30 to 80 nm in diameter. The molecular weight is 10 to 810⁷. Compare with LDL particles, VLDL particles are heterogeneous in size and composition. VLDL particls can be separated in Sf 20-60 and Sf60-400. VLDL consists of protein 10%, phospholipid 19%, free cholesterol 7%, cholesterol ester 10% and triglycerides 56%. Apolipoprotein contribution% apoB 37 apoC 50 apoE 13 Apo B-48 is the sole constituent apolipoprotein on VLDL.It is presumed that the cholesteryl esters and triglycerides form the hydrophobic core, which is surrounded by a surface coat of apolipoprotein B, free cholesterol and polar phospholipid components oriented toward the aqueous medium.
(Ref. 1301/1302/1303/1304/1305/1306)

Structure of Chylomicrons
Chylomicrons is a spherical particle and in normal individuals ranges 75 to 1200 nm in diameter. The average molecular weight is below 410⁸ .Compared with other lipoproteins , Chylomicrons particles are relatively heterogeneous in size and composition . Chylomicrons consists of Protein 1-2% Phospholipid 19% Free cholesterol 1.6% Cholesterol ester 1.4% Triglyceride 88%
Apolipoprotein contribution% apoB 5-20 (mainly apoB48) apoC 70-80 apoE 4 on Chylomicrons. It is presumed that the cholesteryl esters and triglycerides form the hydrophobic core, which is surrounded by a surface coat of apolipoprotein B48, free cholesterol and polar phospholipid components oriented toward the aqueous medium.
(Ref. 1401/1402/1403/1404/1405)

Structure
Lp(a) is made up of a low-density lipoprotein-like structure in which apolipoprotein B-100, the protein moiety of authentic low-density lipoprotein, is covalently linked to a glycoprotein, apolipoprotein (a) ,which is the specific marker of Lp (a) that exhibits a striking similarity to plasminogen. The dominant structural motif of apo (a) is the kringle, a three-disulfide, triple-loop structure named for its resemblance to a Danish pretzel. Kringle 4 is repeated 13 to 37 times, whereas there is only one kringle 5. It is now established that the size of each apo (a) isoform is under strict genetic control and determined by the number of kringles that it contains. Usually, there is 1 mol of apo (a) and 1 mol of apo B-100 in each Lp(a) particle. However, species of Lp (a) having one copy of apo B-100 and 2mol of apo (a) have been reported.
Composition
Lp(a) is heterogeneous, both within and among individuals, and this heterogeneity may at least partly be accounted for by differences in the size of apo (a). The Mr of apo (a) varies among individuals, and no fewer than six isoforms with Mr ranging from 450,000 to 1,000,000 Da have been observed.(Ref. 3007)
Synthesis
The primary site of synthesis of Lp (a) appears to be the hepatocyte, although apo (a) mRNA has also been identified in testes and brain.(Ref. 3008) Synthesis of apo (a) in liver is hardly surprising given that the hepatocyte is also the primary site of the synthesis of apo B-100.

Sites of synthesis:The liver and the small intestine.
The rate of synthesis:11mg/kg/day

Sites of synthesis:The liver and the small intestine.
The rate of synthesis:2.8mg/kg/day

Sites of synthesis: liver
The rate of synthesis:14.4mg/kg/day

Sites of synthesis:The liver and the small intestine.
The rate of synthesis:1.6mg/kg/day

Sites of synthesis:The liver and the small intestine.
The rate of synthesis:5.2mg/kg/day

Sites of synthesis:The liver
The rate of synthesis:5.2mg/kg/day