porphyrins chemistry and metabolism.pptx

Clinical Biochemistry

1. Presentation (Clinical Biochemistry) Group Members 1.Ayesha Imran 2.Kinza Iftikhar 3.Mubeen Akhtar 4.Ahsaan afzal 5.Hammad Raza 6.Shahzeb Hussain

2. Porphyrins, chemistry and metabolism.

3. Porphyrins Porphyrins are cyclic compounds that bind to metallic ions (usually Fe2+ or Fe3+) . Porphyrin + metal = metalloporphyrin. The most prevalent metallopophyrin in human is heme which consists of one Fe2+ coordinated in the center of tetrapyrrol ring through methyl bridges. The porphyrin in heme, with its particular arrangement of four methy two propionate, and the two vinyl substituents, is known as protoporphyrin IX.

4. Porphyrins emit intense red fluorescence when exposed to light at around 400 nm. Thus, spectrofluorometric methods provide very sensitive detection and quantification of porphyrin. The porphyrin isomers differ in the arrangement of the side-chain substituents (e.g. acetyl and propionyl in uroporphyrins; methyl and propionyl in coproporphyrins Some important porphyrins are (Hemoglobin, myoglobin, Cytochromes , catalases, Peroxidases , Tryptophan pyrrolase , EMB-RCG. )

5. Structure(Chemistry) of porphyrins The Porphyrins are complex structures consisting of 4 pyrrole rings united by “methenyl” bridges or (methylidene bridges).

6. Biosynthesis of Porphyrins Site : 1. The major Sites of heme biosynthesis are the Liver. 2.The Initial reaction and the last three steps in the formation of Porphyrins occur in Mitochondria 3.The intermediate steps of the biosynthetic pathway occur in the Cytosol.

7. Biosynthesis of porphyrins Step 1 (Formation of 6-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 o-aminoLevulinic 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 >>>>>& Amino levulinic acid +carbon dioxide+Coenzyme A

8. Biosynthesis of porphyrins Step 2 ( Formation of porphyrinogen ) .This reaction takes place in Cytosol. The dehydrationof two molecules of ALA to form Porphobilinogen by the enzyme ALA dehydrase. The enzyme is inhibited by heavy metal ion lead. .2(&-aminoLevulinic acid )>>>>>porphobilinogen+water (H2O) Step 3 ( Formation of uroporphyrinogen) .The condensation of four molecules of porphyrinogen.It gives Uroporphyrinogen-Ill. This reaction catalyzes by Uroporphyrinogen-I synthatase and uroporphyrinogenIll cosynthatase takes place in cytosol. .4(Phorphobilnogen)>>>>>Uroporphyrinogen III

9. Biosynthesis of porphyrins Step 4 (Formation of Heme) .Uroporphyrinogen-Ill is converted into Heme by a series of decarboxylation and oxidation. Finally the Uroporphyrinogen-Ill converted into Protoporphyrinogen oxidase. The enzyme Protoporphyrin decarboxylase and protoporphyrin oxidase and protoporphy rinogen oxidase. The protoporphyrin-Il is modified into heme by substituting the ferrous ion (Fe+3) by the enzyme ferrochelation Urophorpyrinogen-III>>>>>Protoporphyrin IX +6 Carbon dioxide Protoporphrin IX +Fe +3>>>>>HEME

10. Porphyrin(Heme synthesis)

11. Porphyrins (chlorophyll synthesis)

12. Regulation of Heme Biosynthesis The two major sites of heme biosynthesis are erythroid cells, which synthesize ~85% of the body's heme groups, and the liver, which synthesizes ~ 80% of the remainder. An important function of heme in liver is as the prosthetic groups of the cytochromes P450, a family of oxidative enzymes involved in detoxification, whose members are required throughout a liver cell's lifetime in amounts that vary with conditions. In contrast, erythroid cells, in which heme is, of course, a hemoglobin component, engage in heme synthesis only on differentiation, when they synthesize hemoglobin in vast quantities.This is a onetime synthesis; the heme must last the erythrocyte's lifetime (normally 120 days) since heme and hemoglobin synthesis stop on red cell maturation (protein synthesis stops on the loss of nuclei and ribosomes). The different ways in which heme biosynthesis is regulated in liver and in erythroid cells reflect these different demands: In liver, heme biosynthesis must really be "controlled," whereas in erythroid cells, the process is more like breaking a dam.

13. Continue..... In Liver : The main control target in heme biosynthesis is ALA synthase, the enzyme catalyzing the pathway's first committed step. Heme, or its Fe(III) oxidation product hemin, controls this enzyme's activity through three mechanisms: Feedback inhibition : inhibition of the transport of ALA synthase (ALAS) from its site of synthesis in the cytosol to its reaction site in the mitochondrion, andrepression of ALAS synthesis. In Erythrocytes : In erythroid cells, heme exerts quite a different effect on its biosynthesis. Heme induces, rather than represses, protein synthesis in reticulocytes (immature erythrocytes).

14. Continue.... . Moreover, the rate-determining step of heme biosynthesis in erythroid cells may not be the ALA synthase reaction. . Experiments on various systems of differentiating erythroid cells implicate ferrochelatase and porphobilinogen deaminase in the control of heme biosynthesis in these cells. There are also indications that cellular uptake of iron may be rate limiting. Iron is transported in the plasma complexed with the iron transport protein transferrin. The rate at which the iron-transferrin complex enters most cells, including those of liver, is controlled by receptormediated endocytosis. However, lipid-soluble iron complexes that diffuse directly into reticulocytes stimulate in vitro heme biosynthesis.

15. Heme degradation Site of Heme degradation - cells of the reticulo endothelial system in spleen, liver and bone marrow

16. Heme degradation

17. Heme degradation Most of the heme which is degraded comes from hemoglobin in red blood cells, which have a life span of about 120 days. There is thus a turnover of about 6 g/day of hemoglobin. Normally , senescent red blood cells and heme from other sources are engulfed by cells of the reticuloendothelial system. . The globin is recycled or converted into amino acids, which in turn are recycled or catabolized as required. Heme is oxidized.

18. Effects of drugs on ALA synthase activity .The activity of ALA synthase is markedly increased by the administration of a large number of drugs e.g. phenobarbital, insecticides, carcinogens etc. . These compounds are mostly metabolized by a heme containing protein, cytochrome P450. On administration of drugs, cellular levels of heme are depleted due to its increased incorporation into cytochromeP450.

19. Continue... The reduced heme concentration increases the synthesis
(derepression) of ALA synthase to meet the cellular demands.
Regulation in the erythroid cells:
The enzyme ALA synthase does not appear to control the heme synthesis in the erythroid cells.
Uroporphyrinogen synthase & ferrochelatse mostly regulate heme formation in these cells

20. Clinical features: 1.The patients are photosensitive (itching and burning of skin when exposed to visible light) due to the abnormal porphyrins that accumulate.
2. Increased hemolysis is also observed in the individuals affected by this disorder.
3. The individuals excrete uroporphyrinogen and coproporphyrinogen which oxidize respectively to uroporphyrin and coproporphyrin (red pigments).

21. Applications In macular degeneration using verteporfin In phototherapy to treat bacterial infections, such as acne studied as catalysts for the oxidation of organic compounds emulate the action of various heme enzymes such as cytochromeP450, lignin peroxidase. In molecular electronics and supramolecular building blocks

22. Continue... To construct structures in supramolecular chemistry.
The study of the impacts and processes that organisms have had on the Earth, had its origins in the isolation of porphyrins from petroleum.
The study of the impacts and processes that organisms have had on the Earth, had its origins in the isolation of porphyrins from petroleum.

23. Conclusion Synthesis of porphyrins occurs in animals for haem production and in plants for chlorophyll production. Distribution pattern of porphyrin in urine serves as functional fingerprint of toxicity.

24. References HARPER'S ILLUSTRATED BIOCHEMISTRY (28TH EDITION) by robert murray, david A.bender,peter j kennekky, victor w rodwell,p.antony weil. (page No-271). Biochemistry Lippincott's Illustrated Reviews by RichardHarvey& Denise Ferrier. Slidesshare .net