Download MBBS Biochemistry PPT 6 L7 Lipoprotein Lecture Notes

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? Lipoproteins are types of

Compound Lipids /Conjugated

Proteins.

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? Lipoproteins are macromolecules

formed by aggregation of :

? Lipids (Neutral and Amphipathic )

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? Proteins( Apoprotein) in the

human body.

? Lipoproteins acquire polarity

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(Hydrophilic Property)
? Lipoprotein serve as vehicles

for transportation of Neutral

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and Amphipathic Lipids

through aqueous media blood

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and lymph.

?Lipoproteins are

biosynthesized within the

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cells of tissues.

?By aggregation of various

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forms of Lipids and

Apoproteins.

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Structure Of Lipoproteins


Structure of Lipoproteins

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? The non polar /hydrophobic Lipids TAG and

Cholesterol Ester are gathered central y to

form the core of LipoProtein particle.

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? At the periphery of Lipoprotein are

Apoprotein and Amphipathic Lipids viz

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Phospholipids and Cholesterol.


? The Apoprotein and polar groups of

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Amphipathic Lipids impart

hydrophilic property to Lipoprotein

molecules

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? This helps in transportation of

Lipids

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? From site of origin to site of

utilization through blood.

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Cholesterol Transported as Lipoprotein

Complex (LDL)
Functions Of Lipoproteins

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? Lipoproteins serve as a vehicle in

transportation of non polar Lipids

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? From the site of its biosynthesis to

the site of utilization through

aqueous media of blood or lymph.

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Types Of Lipoproteins
? Depending upon the composition and other

properties following are the types of

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Lipoproteins:

?Chylomicrons (CM)
?Very Low Density Lipoprotein (VLDL)

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?Low Density Lipoproteins (LDL)
?High Density Lipoproteins (HDL)
?Free Fatty acid -Albumin

Lipoproteins

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Lipoproteins

Types of Lipoprotein

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(al contain characteristic amounts TAG, cholesterol, cholesterol esters,

phospholipids and Apoproteins ? NMR Spectroscopy)

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Diameter

Major

Class

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(nm)

Source and Function

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Apoliproteins

Chylomicrons

500

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Intestine. Transport of

A, B48,

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(CM)

Largest

dietary TAG

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C(I,II,III) E

ty

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Very low density

43

Liver. Transport of

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B100,

si

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lipoproteins

endogenously

C(I,II,III) , E

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(VLDL)

synthesised TAG

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n
g

d
en

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Low density

22

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Formed in circulation by

B100

lipoproteins

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partial breakdown of IDL.

(LDL)

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Delivers cholesterol to

I
n
creasi

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peripheral tissues

High density

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8

Liver. Removes "used"

A, C(I,II,III),

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lipoproteins

Smal est

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cholesterol from tissues

D, E

(HDL)

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and takes it to liver.

Donates apolipoproteins to

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CM and VLDL
Features Chylomicrons VLDL

LDL

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HDL

Site of

Small

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Hepatocytes

Blood

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Nascent HDL

Synthesis Intestine

Liver -80%

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Circulation Liver

Intestine -20% From VLDL

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Lipids %

99%

92%

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80%

50%

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Protein % 1%

8%

20%

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50%

Rich Lipid TAG

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TAG

Cholester Phospholipids

Form

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Exogenous

Endogenous ol

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Associate Apo B48, Apo Apo B100,Apo Apo B100, Apo A I,Apo A II

d

CI ,Apo E

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CI,Apo CI ,Apo Apo CI,

Apo C I, Apo C II

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Apoprote

E

Apo CI

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Apo D & Apo E

in

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and Apo E

Transport Dietary Lipids Liver

Liver

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Extrahepatic

From

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Intestine

Tissues

Transport Liver

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Extrahepatic Extrahepa Liver

To

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Tissues

tic Tissues

HDL Has Scavenging Role

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OR

Reverse Transport of

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Cholesterol


HDL Is Associated

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With Enzyme LCAT

Responsible For

Cholesterol

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Esterification And Its

Excretion
? HDL has scavenging role with

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protective mechanism.

? HDL Transports Cholesterol from
Extrahepatic tissues back to Liver for

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its excretion.

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? HDL reduces risk of

Atherosclerosis.

? HDL clears the body Lipids and

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do not al ow accumulation of

Lipids in blood.
?Thus when the levels of

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HDL are within normal

range

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?Cholesterol associated

with HDL is termed as

Good Cholesterol

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? Based on Electrophoretic pattern

the Lipoproteins are termed as:

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?LDL: Beta Lipoproteins
?VLDL: Pre Beta Lipoproteins
?HDL: Alpha Lipoproteins
Classification of plasma Lipoproteins

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according to their electrophoretic

mobility

(CM)

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a-lipoprotein (HDL)
Pre-b-Lipoprotein (VLDL)
b-lipoprotein (LDL)
CM

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Lipoprotein

Density Diameter

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Protein % Phospholi Triacyl-

class

(g/mL)

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(nm)

of dry wt

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pids %

glycerols %

of dry wt

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HDL

1.063-

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5 ? 15

50

29

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8

1.21

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LDL

1.019 ? 18 ? 28

25

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21

4

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1.063

IDL

1.006-

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25 - 50

18

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22

31

1.019

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VLDL

0.95 ?

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30 - 80

10

18

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50

1.006

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Chylomicrons

< 0.95

100 - 500

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1 - 2

7

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84

99

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Physical properties and lipid compositions of Lipoproteins

CM

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VLDL

LDL

HDL

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Density (g/ml)

< 0.94 0.94-1.006 1.006-1.063 1.063-1.210

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6000-

Diameter (?)

2000

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600

250

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70-120

Total lipid (wt%) * 99

91

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80

50

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Triacylglycerol

85

55

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10

6

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Cholesterol esters 3

18

50

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40

Cholesterol

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2

7

11

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7

Phospholipid

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8

20

29

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46

Apoprotein % 1 9 20 50

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Fatty acid compositions (wt% of the total) in the main lipids of human Lipoprotein

Triacylglycerols Cholesterol

Esters

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Phospholipids

Fatty acid VLDL LDL HDL VLDL

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LDL HDL VLDL LDL HDL

16:0 27

23 23

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12

11 11

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34

36

32

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18:0 3

3

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4

1

1

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1

15

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14

14

18:1 45

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47 44

26

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22 22

12

12

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12

18:2 16

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16 16

52

60 55

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20

19

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21

20:4

(n-6) 2

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5

8

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6

7

6

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14

13

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16
The main properties of the Apoproteins.*

Apoprotein

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Molecular weight

Lipoprotein

Function

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Lecithin:cholesterol

Apo A1

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28,100

HDL

acyltransferase (LCAT)

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activation. Main structural

protein.

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Apo A2

17,400

HDL

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Enhances hepatic lipase

activity

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Apo A4

46,000

CHYLOMICRON(CM)

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Apo AV(5)

39,000

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HDL

Enhances triacylglycerol

uptake

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Apo B48

241,000

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CHYLOMICRON

Derived from Apo B100 ?

lacks the LDL receptor

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Apo B100

512,000

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LDL, VLDL

Binds to LDL receptor

Apo C1

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7,600

VLDL, CM

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Activates LCAT

Apo C2

8,900

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VLDL, CM

Activates lipoprotein lipase

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Apo C3

8,700

VLDL, CM

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Inhibits lipoprotein lipase

Apo D

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33,000

HDL

Associated with LCAT,

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progesterone binding

Apo E

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34,000

HDL

At least 3 forms. Binds to

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LDL receptor
Linked by disulfide bond to

Apo(a)

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300,000-800,000

LDL, Lp(a)

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apo B100 and similar to

plasminogen

Apo H, J, L

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Poorly defined functions

Apo M

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HDL

Transports sphingosine-1-

phosphate

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* Roman numerals are sometimes used to designate apoproteins (e.g. Apo AI, AI , AI I, etc)

Disorders Of Lipoproteins

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? Defect in Lipoprotein

metabolism leads to

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Lipoprotein disorders:

? Hyperlipoproteinemias
? Hypolipoproteinemias

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Lipoproteins Atherogenic Particles

MEASUREMENTS:

Apolipoprotein B

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Non-HDL-C

VLDL

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VLDL

IDL

R

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LDL

Small,

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dense

TG-rich lipoproteins

LDL

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? Defect in the receptors of

Lipoproteins on specific

tissues

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? Leads to retention of

specific Lipoproteins in the

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blood circulation.

? Abnormal high levels of LDL in

blood is due to LDL receptor

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defect on extrahepatocytes

bad to body.
? The Cholesterol associated to

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high LDL levels is said to be

bad Cholesterol.

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? This increases the risk of

Atherosclerosis ,Ischemia, MI

and Stroke.

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? Recently evidenced high levels

of blood HDL are also bad to

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body.

? This increases the risk of

Atherosclerosis ,Ischemia, MI

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and Stroke.
Proteolipids/ Lipophilin

Proteolipids/ Lipophilin

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? Proteolipids are compound lipids

which have more content of

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Proteins than Lipids.

? Proteolipid is a transmembrane

domain protein bound with Lipids.

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Occurrence Of Proteolipids

? Proteolipids are structural

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Lipids

? Present on the extracel ular

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side of the membrane.

? Proteolipids are also present in

Myelin Sheath.

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