Porphyrins are cyclic organic compounds that are precursors to important enzymes and pigments like heme, chlorophyll, and cytochromes. Heme synthesis involves multiple steps starting with the condensation of glycine and succinyl-CoA to form delta-aminolevulinic acid, followed by further reactions to form porphobilinogen, uroporphyrinogen III, protoporphyrin IX, and finally heme upon chelation with iron. Porphyrin metabolism is related to chromoproteins like hemoglobin, methemoglobin, sulfhemoglobin, carboxyhemoglobin, metalbumin, and myoglobin which contain heme and transport or store oxygen in vertebrates and some

1. PORPHYRIN METABOLISM
and
its related
Chromoproteins
Submitted by:
AKANCHA SINHA
M17LS01

2. Porphyrin-An Introduction
• are a group of heterocyclic macrocycle
organic compounds, composed of four
modified pyrrole subunits interconnected
at their α carbon atoms via methine bridges
(=CH−). The parent porphyrin is porphine ,
a rare chemical compound.

4. Porphyrins are cyclic compounds that are the precursors of
heme and other important enzymes and pigments.
Heme is the complex of iron and porphyrin that unites with
the protein globin to form haemoglobin.

5. Heme Synthesis : Synthesis of Porphyrin Molecule
• Heme is the non-protein part mainly
present in that mean which is one of
the constituent of Hemoglobin,
Chlorophyll, Myoglobin and
Cytochromes.
• Heme is a porphyrin nucleous which
have tetra pyrrole ring.
• In the structure of heme.
• It contains 4 pyrrole nucleus is
connected by methylene bridges
• It is a plannar molecule. The ring
contains Vinyl groups (-CH=CH2),
Methyl group (-CH3), Propionic acid
groups (-CH2-CH2-COOH).
• The biosynthesis of heme mainly
takes place partly in Mitochondria and
partly in cytosol of the liver.
• The two major sites of heme
biosynthesis are Erythroid cells, which
synthesizes most of the remainder.
• The synthesis can be explained in
several steps.

6. Steps of Heme synthesis
• Step 1:
Formation of δ-amino Levulinic acid
(ALA):
The precursor molecule for the heme synthesis is simplest
and non-essential and optically inactive amino acid Glycine
and the TCA cycle intermediate Succinyl~coA enzyme.
Glycine condenses with Succinyl~coA. It forms δ-amino
Levulinic acid. This reaction catalyzed by ALA synthatase.
This reaction is takes place in mitochondria. This is the rate
limiting step of this pathway.
Glycine + Succinyl~coA → δ-amino Levulinic acid
+ CO2 + CoenzymeA
• Step 2:
Formation of Porphyrinogen:
This reaction takes place in Cytosol. The dehydration of
two molecules of ALA to form Porphobilinogen by the
enzyme ALA dehydrase. The enzyme is inhibited by heavy
metal ion lead.
2 (δ-amino Levulinic acid) → Porphobilinogen +
H2O

7. • Step 3:
Formation of Uroporphyrinogen:
The condensation of four molecules of porphyrinogen.
It gives Uroporphyrinogen-III. This reaction catalyzes by
Uroporphyrinogen-I synthatase and uroporphyrinogen-
III cosynthatase takes place in cytosol.
4 (Phorphobilinogen) →Uroporphyrinogen-III
• Steps 4:
Formation of Heme:
Uroporphyrinogen-III is converted into Heme by a series
of decarboxylation and oxidation. Finally the Uro-
porphyrinogen-III converted into Protoporphyrinogen
oxidase. The enzyme Protoporphyrin decarboxylase
and protoporphyrin oxidase and protoporphyrinogen
oxidase. The protoporphyrin-II is modified into heme by
substituting the ferrous ion (Fe+3) by the enzyme
ferrochelation.
Uroporphyrinogen-III →→→ Protoporphyrin-
IX +
6 Carbondioxide
Protoporphyrin-IX + Fe+3 →HEME

9. Chromoproteins related to Porphyrin
Metabolism
A chromoprotein is a conjugated protein that contains a pigmented
prosthetic group (or cofactor).
They are:
• HAEMOGLOBIN
• METHAEMOGLOBIN
• SULPHOHAEMOGLOBIN
• CARBOXYHAEMOGLOBIN
• METALBUMIN
• MYOGLOBIN

10. HAEMOGLOBIN
is the iron-containing oxygen-transport
metalloprotein in the red blood cells of all
vertebrates as well as the tissues of some
invertebrates. Haemoglobin in the blood
carries oxygen from the lungs or gills to
the rest of the body (i.e. the tissues).
There it releases the oxygen to permit
aerobic respiration to provide energy to
power the functions of the organism

11. METHAEMOGLOBIN
is a form of the oxygen-carrying
metalloprotein hemoglobin, in which the
iron in the heme group is in the Fe3+
(ferric) state, not the Fe2+ (ferrous) of
normal hemoglobin. Methemoglobin cannot
bind oxygen, unlike oxyhemoglobin. It is
bluish chocolate-brown in color. In human
blood a trace amount of methemoglobin is
normally produced spontaneously, but when
present in excess the blood becomes
abnormally dark bluish brown. The NADH-
dependent enzyme methemoglobin
reductase (a type of diaphorase) is
responsible for converting methemoglobin
back to hemoglobin.

12. SULPHOHAEMOGLOBIN
is a rare condition in which there is excess
sulphohaemoglobin (SulfHb) in the blood.
The pigment is a greenish derivative of
hemoglobin which cannot be converted
back to normal, functional hemoglobin. It
causes cyanosis even at low blood levels.
It is a rare blood condition that occurs
when a sulfur atom is incorporated into the
hemoglobin molecule. When hydrogen
sulfide (H2S) (or sulfide ions) and ferric
ions combine in the blood, the blood is
incapable of carrying oxygen.

13. CARBOXYHAEMOGLOBIN
is formed when carbon monoxide (CO) binds to the
ferrous iron found in haemoglobin .
Haemoglobin’s affinity for CO is 218 times greater
than that for oxygen (O2), which results in CO
displacing O2 during competition for haem binding
sites. Low concentrations of CO in inhaled air can
cause rapid formation of COHb; 0.1% CO can result in
50% of haemoglobin converting to COHb and notable
clinical symptoms will arise within one hour. Levels of
0.2% CO can lead to death within a few hours.
Although CO binds to haemoglobin at a slower rate
than O2, its greater binding affinity means that it is
released 10,000 more slowly from haemoglobin .

14. METALBUMIN
A form of albumin found in
ascitic and certain serous fluids.
It is sometimes regarded as a
mixture of albumin and mucin.

15. MYOGLOBIN
is an iron- and oxygen-binding protein
found in the muscle tissue of
vertebrates in general and in almost
all mammals.
It is not related to hemoglobin, which
is the iron- and oxygen-binding
protein in blood, specifically in the red
blood cells.