Serum Lipoproteins

Lipoproteins are macromolecular complexes that consist of discrete particles and are composed of both lipids and proteins. The lipids include cholesterol, phospholipids, and triacylglycerols (TAG). A portion of serum cholesterol is esterified with a fatty acid; the remainder is unesterified. The protein components go by the name of apolipoproteins. The major forms of apolipoproteins and their functions

Table 1 Apolipoproteins of serum lipoproteins

Apolipoprotein

Function

A-I

Major apolipoprotein of HDL

Activator of LCAT

A-I

Structural apolipoprotein of HDL (other

functions unknown)

A-IV

Apolipoprotein of chylomicrons (other

functions unknown)

B-48

Chylomicron assembly and secretion

B-100

VLDL assembly and secretion

Ligand for LDL receptor unknown

C-I

Unknown

C-II

Activator of LPL

C-III

Inhibitor of LPL

E

Apolipoprotein of remnant lipoproteins

Ligand for LDL receptor

Promotes hepatic uptake of remnants

Abbreviations: HDL, high-density lipoproteins; LDL, low-density lipoproteins; VLDL, very low-density lipoproteins; LCAT, lecithin cholesterol acyl transferase; LPL, lipoprotein lipase.

Abbreviations: HDL, high-density lipoproteins; LDL, low-density lipoproteins; VLDL, very low-density lipoproteins; LCAT, lecithin cholesterol acyl transferase; LPL, lipoprotein lipase.

are listed in Table 1. Four categories of lipoproteins that carry cholesterol in the serum are chylomicrons, very low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). The characteristics and metabolism of each lipoprotein will be reviewed briefly.

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