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Review ofLiterature
5. High density lipoproteins: are oftwo main types, HDL2 and HDL3.
They probably transported from peripheral cells to the liver, prior to
excrerion (Beckett, 1998).
The apolipoproteins:
The protein components ofthe lipoproteins, the apolipoproteins are
a complex family of polypeptides that promote and control the lipid
transport in plasma and uptake into tissues. They are classified into five
main groups (ape-A, B, C, E and (a)), some ofwhich may be subdivided,
and lastly apo (a).
Apo A: these are synthesized in the liver and intestine. They are initially
present in chylomicrons in lymph, but they rapidly transfer to lIDL.
Apo B: is present in plasma in two forms, apoB100 and apoB48 chyle
micron. ApaB100 is the protein component of LDL and is also present in
VLDL and LDL . ApoB100 is recognized by specific receptors in
peripheral tissues.
Apo C: is a family of three proteins (apo CI, apo ClI and apo ClII) is
synthesized in the liver and incorporated into HDL and LDL,
chylomicron.
Apo E: is synthesized in the liver, incorporated into HDL and transferred
in the circulation to chylomicrons and VLDL. There are three major
isoforrns (apoE2, apoE3 and apoE4) at a single genetic locus giving rise
to genotypes (E3/3, E2/3, E2/4, etc.).
Apo E is probably mainly involved in the hepatic intake of
chylomicron remnants and IDL,
tissues (Walker, 1990).
since it binds to apo B receptors in-the
Lipoprotein (a) "LP (a)":
The lipoprotein (a) is sixth type oflipoprotein particles. It was first
deteced in 1962. It consists of LDL particle to which a long polypeptide
chain is attached by a disulfide bridge a single apo (a) having a high
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