J.'.~"";i'

Introduction:
L1POROTEIN (a)
Review ofLiterature
Cholesterol and its esters, triglycerides and phosholipids are all
transported in plasma as lipoprotein particles. Free Fatty acids are
transported bound to albumin. Lipoprotein particles comprise a peripheral
envelope, consisting mainly ofphospholipids and free cholesterol (which
have both water soluble polar and lipid soluble non-polar groups) with
some apolipoproteins and a central non-polar core (mostly triglycerides
and esterified cholesterol). The molecules in the envelope are distributed
in a single in such a way that the polar groups face out towards the
surrounding plasma, while the non-polar face inwards forming the lipid
core in which the insoluble lipids are carried (Smith, 1990).
Most lipoproteins are assembled in the liver or small intestine. Five
main types oflipoprotein particles can be recognized:
1. Chylomicrons: are large particles (largest size). consisting mainly of
triglyserides 83% added to cholesterol and phosphate. They have the
lowest density. They are formed in intestinal mucosa and reach systemic
circulation via thoracic duct. They are the principle form in which dietary
triglycerides are carried to the tissues.
2. Very low density lipoproteins (YLDL): They are moderately large
particles whose main component is of neutral lipid 78% (endogenous)
added to cholesterol and phospholipid. They are mainly formed in liver
and to a lesser extent by intestinal mucosa and are secreted into plasma
from these two sites.
3. Intermediate density lipoproteins (IDL or VLDL remnants:
Arise from removal of triglycerides from VLDL during the
transition from VLDLto LDL.
4. Low-density lipoproteins (LDL): are cholesterol-rich particles,
formed from IDL by the removal of more triglyceride and apolipoprotein
A orB48 .
60
''1
.....