Porphyrin metabolism
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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
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Porphyrin metabolism
- 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.