Chapter 16

Hemal Biochemistry

The biochemistry and molecular biology department of CMU

• Composition of the blood

– The liquid element: plasma

– The formed elements: red blood cells (ery

throcytes), white blood cells (leukocytes),

and platelets (thrombocytes).

• Plasma --- The blood fraction obtained after

removal of the cellular components.

• Serum --- The liquid element obtained by allo

wing the blood to clot.

§1 Heme Synthesis

Sites:

Mitochondria and cytoplasm

Precursors:

Glycine, succinyl CoA, Fe2+

1. Synthetic pathway of heme

(1) The formation of -aminolevulinic acid (ALA)

+HSCoA + CO2

ALA synthase (pyridoxal phosphate)

In the mitochondria

COOH

H2C

CH2

C¡«SCoA

O

CH2NH2

COOH

COOH

H2C

CH2

C

CH2NH2

O

(2) The formation of porphobilinogen (PBG)

ALA dehydratase

2H2O

In the cytosol

NH

OH

O

OH

O

NH2

COOH

CH2

CH2

C

C

N

O

H H

H H

(3) The formation of uroporphyrinogen (UⅢPG ) and coproporphyrinogen (CPGⅢ Ⅲ

) Ⅲ

4× Porphobilinogen Linear tetrapyrrol

UPGⅢCPGⅢ

Deaminase

UPG Ⅲisomerase

UPGⅢdecarboxylase

In the cytosol

Protoporphyrinogen Ⅸ

Protoporphyrin ⅨHeme ferrochelatase

(4) The formation of heme

CPGⅢoxidase

CPGⅢ

Protopor- phyrinogen Ⅸoxidase

In the mitochondria

                               

         

Heme

Protoporphyrin Ⅸ

Protoporphyrinogen Ⅸ CPGⅢ UPGⅢ

Linear tetrapyrrol

PBG

Gly

succinyl CoA

(1) ALA synthase

•Rate-limiting enzyme

•Feedback-inhibition by heme

•Intensity inhibition by Ferriheme

•Inducing by some drugs and hormones (eg. testosterone)

2. Regulation of heme biosynthesis

(3) Erythropoietin (EPO) can increase sy

nthesis of heme and hemoglobins.

(2) ALA dehydrase and ferrochelatase

Inhibited by heme, and heavy metals.

§2

Metabolism of Bile

Pigment and Jaundice

bile pigment is the main catabolic p

roduct of iron porphyrin compound in t

he body, consisting of bilirubin, biliver

din, bilinogen and bilin.

＊ The source of bilirubin

The compounds involving iron pr

ophyrin in the body are hemoglobin,

myoglobin, cytochrome, peroxidase,

and catalase, etc.

1. Formation and transport of bilirubin

＊ Formation of bilirubin

• site

In the microsome and cytosol of monokaryon- macrophage system of the liver, spleen, and bone marrow.

N N

NN

HOOC

Fe2+

COOH

2O2

NADPH+H+

NADP+

COFe3+

HN

HN

P

N

P

HNO O

NADPH+H+

NADP+

HN

HN

PP

HNO O

HH

heme

biliverdin

bilirubin

heme oxygenase

biliverdin reductase

HN

¦Ä

¢ô ¢ó

¢ò¢ñ

¦Ã

¦Â

¦Á

• process

The spatal structure of bilirubin

N

N H

N

N

O

CO

OO

H

C

O

H

HOH

H

• property

hydrophobic

＊ Transport of Bilirubin

•Form of Transport

Bilirubin-albumin complex

2. Bilirubin conversion in liver

＊ Uptake

＊ Transport

Smooth Endoplasmic reticulum

Combine with ligandin

＊ Conjugation

Bilirubin monoglucuronide

bilirubin

UDPUDP-glucuronyl transfe

rase

UDPGA

Bilirubin diglucuronide

UDPGA

UDPUDP-glucuronyl transfe

rase

structure of bilirubin diglucuronide

HN

HN

HN

HNO O

HH

H2C CH2

CH2

CO

O

CH2

CO

OO

H

HO

H

H

OH

COOH

HH

OH

O

H

OH

HO

H

H

H

OH

H

COOH

＊ Excretion

Conjugated bilirubin is secreted

into the bile and then excreted into the

intestine.

Conjugated bilirubin

bilinogen

coliform

Glucuronic acid

Bilinoxidized

＊ process

3. Metabolism bilirubin in the intestine

Free bilirubin

reduced

NHN

PP

NHO OHHH

bilirubin

H H

+8H

d-urobilinogen

+8H

HN

HN

HN

PP

NHO OHHHH

N

NHN

PP

NHO OHHHH

NH H H H

H HH HH

mesobilirubinogen

d-urobilin

HN

HN

PP

NHO OHHHH

NH HH HH

H HH H

stercobilinogen (l-urobilinogen)

+4H

stercobilin (l-urobilin)

H H

2H

2H

Bilinogen enterohepatic circulation

In the terminal ileum and large i

ntestine, a small fraction of the urob

ilinogens is reabsorbed and reexcret

ed through the liver to constitute the

enterohepatic cycle of urobilinogen.

Hb

globin

heme

NADPH+H+

NADP+

biliverdin

bilirubin

2O2

H2O

Fe3+

+CO

NADPH+H+

NADP+

bilirubin-albumincomplex

bilirubin

ligandin bilirubin-ligandincomplex

bilirubin glucuronide

UDPGA

UDPER

cytosol

liver cellmonokaryon-macrophage cell blood

intestine

glucuronic acid

bilirubin

bilinogen

bilinogen (a little)

bilin

feces

kidneya small fraction

a large fraction

bilinogenO2O2

bilin

urine

bilirubin glucuronide

4. Serum bilirubin and jaundice

• Conjugated bilirubin is also called dire

ct reacting bilirubin or hepatobilirubin.

＊ Serum bilirubin

1 ～ 16mol/l (0.1 ～ 1mg/dl)

• Free bilirubin is also called indirect re

acting bilirubin or hemobilirubin.

free bilirubi

n conjugated

bilirubin

Binding with Glucuronic acid

no yes

Reacting with the diazo reagent

Slow and indirect

Rapid and direct

solubility in water small large

Discharged via kidney no yes

Pass through the membrane of cell

yes no

difference of two bilirubins

Jaundice

• Hemolytic (prehepatic) jaundice

• Hepatocellular (hepatic) jaundice

• Obstructive (posthepatic) jaundice

Laboratory results in patients with jaundice

normalHemolyticjaundice

Hepatocellularjaundice

Obstructivejaundice

Serum bilirubin

total <1mg/dl >1mg/dl >1mg/dl >1mg/dl

direct 0~ 0.8mg/dl

↑

indirect < 1

Urine bile pigments

urobilirubin – – + + + +

urobilinogen A few ↑ uncertainty ↓

urobilin A few ↑ uncertainty ↓

Color of feces normal dark Simple or normal Clay color

↑↑ ↑

↑↑