Pathways

Porphyria variegata (PV) is a rare inborn error of metabolism (IEM) which arises from a defective gene called PPOX. PPOX is responsible for protoporphyrinogen oxidase. A defect in this enzyme results in the build up of several compounds, including porphobilinogen, 5-aminolevulinic acid, and in feces and urine, porphyrin and coproporphyrin. Of the wide range of symptoms which present themselves in affected individuals, some include abdominal pain, vomiting, and diarrhea. As well as seizures, hallucinations and skin sensitivity to light. Indeed, the skin sensitivity can be so extreme that skin pigmentation changes, scarring and blistering and even hair growth can ensue on exposed areas.

Porphyria variegata (PV) is a rare inborn error of metabolism (IEM) which arises from a defective gene called PPOX. PPOX is responsible for protoporphyrinogen oxidase. A defect in this enzyme results in the build up of several compounds, including porphobilinogen, 5-aminolevulinic acid, and in feces and urine, porphyrin and coproporphyrin. Of the wide range of symptoms which present themselves in affected individuals, some include abdominal pain, vomiting, and diarrhea. As well as seizures, hallucinations and skin sensitivity to light. Indeed, the skin sensitivity can be so extreme that skin pigmentation changes, scarring and blistering and even hair growth can ensue on exposed areas.

Porphyria variegata (PV) is a rare inborn error of metabolism (IEM) which arises from a defective gene called PPOX. PPOX is responsible for protoporphyrinogen oxidase. A defect in this enzyme results in the build up of several compounds, including porphobilinogen, 5-aminolevulinic acid, and in feces and urine, porphyrin and coproporphyrin. Of the wide range of symptoms which present themselves in affected individuals, some include abdominal pain, vomiting, and diarrhea. As well as seizures, hallucinations and skin sensitivity to light. Indeed, the skin sensitivity can be so extreme that skin pigmentation changes, scarring and blistering and even hair growth can ensue on exposed areas.

Porphyria variegata (PV) is a rare inborn error of metabolism (IEM) which arises from a defective gene called PPOX. PPOX is responsible for protoporphyrinogen oxidase. A defect in this enzyme results in the build up of several compounds, including porphobilinogen, 5-aminolevulinic acid, and in feces and urine, porphyrin and coproporphyrin. Of the wide range of symptoms which present themselves in affected individuals, some include abdominal pain, vomiting, and diarrhea. As well as seizures, hallucinations and skin sensitivity to light. Indeed, the skin sensitivity can be so extreme that skin pigmentation changes, scarring and blistering and even hair growth can ensue on exposed areas.

The Porphyrin and chlorophyll metabolism happens inside the Arabidopsis thaliana cell. Most of the reaction happen inside the Chloroplast and Mitochondrion. "Porphyrins 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 of porphyrin is porphine, a rare chemical compound of exclusively theoretical interest. Substituted porphines are called porphyrins. Porphyrins are the conjugate acids of ligands that bind metals to form complexes. The metal ion usually has a charge of 2+ or 3+." (Wikipedia, 2020) "Chlorophyll (also chlorophyl) is any of several related green pigments found in the mesosomes of cyanobacteria and in the chloroplasts of algae and plants. Chlorophyll is essential in photosynthesis, allowing plants to absorb energy from light." (Wikipedia, 2020) Alanine, aspartate and glutamate metabolism, Glycine, serine and threonine metabolism, and Riboflavin metabolism are all related pathways to the Porphyrin and chlorophyll metabolism.

The metabolism of porphyrin begins with with glutamic acid being processed by an ATP-driven glutamyl-tRNA synthetase by interacting with hydrogen ion and tRNA(Glu), resulting in amo, pyrophosphate and L-glutamyl-tRNA(Glu) Glutamic acid. Glutamic acid can be obtained as a result of L-glutamate metabolism pathway, glutamate / aspartate : H+ symporter GltP, glutamate:sodium symporter or a glutamate / aspartate ABC transporter . L-glutamyl-tRNA(Glu) Glutamic acid interacts with a NADPH glutamyl-tRNA reductase resulting in a NADP, a tRNA(Glu) and a (S)-4-amino-5-oxopentanoate. This compound interacts with a glutamate-1-semialdehyde aminotransferase resulting a 5-aminolevulinic acid. This compound interacts with a porphobilinogen synthase resulting in a hydrogen ion, water and porphobilinogen. The latter compound interacts with water resulting in hydroxymethylbilane synthase resulting in ammonium, and hydroxymethylbilane. Hydroxymethylbilane can either be dehydrated to produce uroporphyrinogen I or interact with a uroporphyrinogen III synthase resulting in a water molecule and a uroporphyrinogen III. Uroporphyrinogen I interacts with hydrogen ion through a uroporphyrinogen decarboxylase resulting in a carbon dioxide and a coproporphyrinogen I Uroporphyrinogen III can be metabolized into precorrin by interacting with a S-adenosylmethionine through a siroheme synthase resulting in hydrogen ion, an s-adenosylhomocysteine and a precorrin-1. On the other hand, Uroporphyrinogen III interacts with hydrogen ion through a uroporphyrinogen decarboxylase resulting in a carbon dioxide and a Coproporphyrinogen III. Precorrin-1 reacts with a S-adenosylmethionine through a siroheme synthase resulting in a S-adenosylhomocysteine and a Precorrin-2. The latter compound is processed by a NAD dependent uroporphyrin III C-methyltransferase [multifunctional] resulting in a NADH and a sirohydrochlorin. This compound then interacts with Fe 2+ uroporphyrin III C-methyltransferase [multifunctional] resulting in a hydrogen ion and a siroheme. The siroheme is then processed in sulfur metabolism pathway. Uroporphyrinogen III can be processed in anaerobic or aerobic condition. Anaerobic: Uroporphyrinogen III interacts with an oxygen molecule, a hydrogen ion through a coproporphyrinogen III oxidase resulting in water, carbon dioxide and protoporphyrinogen IX. The latter compound then interacts with an 3 oxygen molecule through a protoporphyrinogen oxidase resulting in 3 hydrogen peroxide and a Protoporphyrin IX Aerobic: Uroporphyrinogen III reacts with S-adenosylmethionine through a coproporphyrinogen III dehydrogenase resulting in carbon dioxide, 5-deoxyadenosine, L-methionine and protoporphyrinogen IX. The latter compound interacts with a meanquinone through a protoporphyrinogen oxidase resulting in protoporphyrin IX. The protoporphyrin IX interacts with Fe 2+ through a ferrochelatase resulting in a hydrogen ion and a ferroheme b. The ferroheme b can either be incorporated into the oxidative phosphorylation as a cofactor of the enzymes involved in that pathway or it can interact with hydrogen peroxide through a catalase HPII resulting in a heme D. Heme D can then be incorporated into the oxidative phosphyrlation pathway as a cofactor of the enzymes involved in that pathway. Ferroheme b can also interact with water and a farnesyl pyrophosphate through a heme O synthase resulting in a release of pyrophosphate and heme O. Heme O is then incorporated into the Oxidative phosphorylation pathway.

This pathway depicts the synthesis and breakdown of porphyrin. The porphyrin ring is the framework for the heme molecule, the pigment in hemoglobin and red blood cells. The first reaction in porphyrin ring biosynthesis takes place in the mitochondria and involves the condensation of glycine and succinyl-CoA by delta-aminolevulinic acid synthase (ALAS). Delta-aminolevulinic acid (ALA) is also called 5-aminolevulinic acid. Following its synthesis, ALA is transported into the cytosol, where ALA dehydratase (also called porphobilinogen synthase) dimerizes 2 molecules of ALA to produce porphobilinogen. The next step in the pathway involves the condensation of 4 molecules of porphobilinogen to produce hydroxymethylbilane (also known as HMB). The enzyme that catalyzes this condensation is known as porphobilinogen deaminase (PBG deaminase). This enzyme is also called hydroxymethylbilane synthase or uroporphyrinogen I synthase. Hydroxymethylbilane (HMB) has two main fates. Most frequently it is enzymatically converted into uroporphyrinogen III, the next intermediate on the path to heme. This step is mediated by two enzymes: uroporphyrinogen synthase and uroporphyrinogen III cosynthase. Hydroxymethylbilane can also be non-enzymatically cyclized to form uroporphyrinogen I. In the cytosol, the uroporphyrinogens (uroporphyrinogen III or uroporphyrinogen I) are decarboxylated by the enzyme uroporphyrinogen decarboxylase. These new products have methyl groups in place of the original acetate groups and are known as coproporphyrinogens. Coproporphyrinogen III is the most important intermediate in heme synthesis. Coproporphyrinogen III is transported back from the cytosol into the interior of the mitochondria, where two propionate residues are decarboxylated (via coproporphyrinogen-III oxidase), which results in vinyl substituents on the 2 pyrrole rings. The resulting product is called protoporphyrinogen IX. The protoporphyrinogen IX is then converted into protoporphyrin IX by another enzyme called protoporphyrinogen IX oxidase. The final reaction in heme synthesis also takes place within the mitochondria and involves the insertion of the iron atom into the ring system generating the molecule known heme b. The enzyme catalyzing this reaction is known as ferrochelatase. The largest repository of heme in the body is in red blood cells (RBCs). RBCs have a life span of about 120 days. When the RBCs have reached the end of their useful lifespan, the cells are engulfed by macrophages and their constituents recycled or disposed of. Heme is broken down when the heme ring is opened by the enzyme known as heme oxygenase, which is found in the endoplasmic reticulum of the macrophages. The oxidation process produces the linear tetrapyrrole biliverdin, ferric iron (Fe3+), and carbon monoxide (CO). The carbon monoxide (which is toxic) is eventually discharged through the lungs. In the next reaction, a second methylene group (located between rings III and IV of the porphyrin ring) is reduced by the enzyme known as biliverdin reductase, producing bilirubin. Bilirubin is significantly less extensively conjugated than biliverdin. This reduction causes a change in the colour of the molecule from blue-green (biliverdin) to yellow-red (bilirubin). In hepatocytes, bilirubin-UDP-glucuronyltransferase (bilirubin-UGT) adds two additional glucuronic acid molecules to bilirubin to produce the more water-soluble version of the molecule known as bilirubin diglucuronide. In most individuals, intestinal bilirubin is acted on by the gut bacteria to produce the final porphyrin products, urobilinogens and stercobilins. These are excreted in the feces. The stercobilins oxidize to form brownish pigments which lead to the characteristic brown colour found in normal feces. Some of the urobilinogen produced by the gut bacteria is reabsorbed and re-enters the circulation. These urobilinogens are converted into urobilins that are then excreted in the urine which cause the yellowish colour in urine.

The metabolism of porphyrin begins with with glutamic acid being processed by an ATP-driven glutamyl-tRNA synthetase by interacting with hydrogen ion and tRNA(Glu), resulting in amo, pyrophosphate and L-glutamyl-tRNA(Glu) Glutamic acid. Glutamic acid can be obtained as a result of L-glutamate metabolism pathway, glutamate / aspartate : H+ symporter GltP, glutamate:sodium symporter or a glutamate / aspartate ABC transporter . L-glutamyl-tRNA(Glu) Glutamic acid interacts with a NADPH glutamyl-tRNA reductase resulting in a NADP, a tRNA(Glu) and a (S)-4-amino-5-oxopentanoate. This compound interacts with a glutamate-1-semialdehyde aminotransferase resulting a 5-aminolevulinic acid. This compound interacts with a porphobilinogen synthase resulting in a hydrogen ion, water and porphobilinogen. The latter compound interacts with water resulting in hydroxymethylbilane synthase resulting in ammonium, and hydroxymethylbilane. Hydroxymethylbilane can either be dehydrated to produce uroporphyrinogen I or interact with a uroporphyrinogen III synthase resulting in a water molecule and a uroporphyrinogen III. Uroporphyrinogen I interacts with hydrogen ion through a uroporphyrinogen decarboxylase resulting in a carbon dioxide and a coproporphyrinogen I Uroporphyrinogen III can be metabolized into precorrin by interacting with a S-adenosylmethionine through a siroheme synthase resulting in hydrogen ion, an s-adenosylhomocysteine and a precorrin-1. On the other hand, Uroporphyrinogen III interacts with hydrogen ion through a uroporphyrinogen decarboxylase resulting in a carbon dioxide and a Coproporphyrinogen III. Precorrin-1 reacts with a S-adenosylmethionine through a siroheme synthase resulting in a S-adenosylhomocysteine and a Precorrin-2. The latter compound is processed by a NAD dependent uroporphyrin III C-methyltransferase [multifunctional] resulting in a NADH and a sirohydrochlorin. This compound then interacts with Fe 2+ uroporphyrin III C-methyltransferase [multifunctional] resulting in a hydrogen ion and a siroheme. The siroheme is then processed in sulfur metabolism pathway. Uroporphyrinogen III can be processed in anaerobic or aerobic condition. Anaerobic: Uroporphyrinogen III interacts with an oxygen molecule, a hydrogen ion through a coproporphyrinogen III oxidase resulting in water, carbon dioxide and protoporphyrinogen IX. The latter compound then interacts with an 3 oxygen molecule through a protoporphyrinogen oxidase resulting in 3 hydrogen peroxide and a Protoporphyrin IX Aerobic: Uroporphyrinogen III reacts with S-adenosylmethionine through a coproporphyrinogen III dehydrogenase resulting in carbon dioxide, 5-deoxyadenosine, L-methionine and protoporphyrinogen IX. The latter compound interacts with a meanquinone through a protoporphyrinogen oxidase resulting in protoporphyrin IX. The protoporphyrin IX interacts with Fe 2+ through a ferrochelatase resulting in a hydrogen ion and a ferroheme b. The ferroheme b can either be incorporated into the oxidative phosphorylation as a cofactor of the enzymes involved in that pathway or it can interact with hydrogen peroxide through a catalase HPII resulting in a heme D. Heme D can then be incorporated into the oxidative phosphyrlation pathway as a cofactor of the enzymes involved in that pathway. Ferroheme b can also interact with water and a farnesyl pyrophosphate through a heme O synthase resulting in a release of pyrophosphate and heme O. Heme O is then incorporated into the Oxidative phosphorylation pathway.

This pathway depicts the synthesis and breakdown of porphyrin. The porphyrin ring is the framework for the heme molecule, the pigment in hemoglobin and red blood cells. The first reaction in porphyrin ring biosynthesis takes place in the mitochondria and involves the condensation of glycine and succinyl-CoA by delta-aminolevulinic acid synthase (ALAS). Delta-aminolevulinic acid (ALA) is also called 5-aminolevulinic acid. Following its synthesis, ALA is transported into the cytosol, where ALA dehydratase (also called porphobilinogen synthase) dimerizes 2 molecules of ALA to produce porphobilinogen. The next step in the pathway involves the condensation of 4 molecules of porphobilinogen to produce hydroxymethylbilane (also known as HMB). The enzyme that catalyzes this condensation is known as porphobilinogen deaminase (PBG deaminase). This enzyme is also called hydroxymethylbilane synthase or uroporphyrinogen I synthase. Hydroxymethylbilane (HMB) has two main fates. Most frequently it is enzymatically converted into uroporphyrinogen III, the next intermediate on the path to heme. This step is mediated by two enzymes: uroporphyrinogen synthase and uroporphyrinogen III cosynthase. Hydroxymethylbilane can also be non-enzymatically cyclized to form uroporphyrinogen I. In the cytosol, the uroporphyrinogens (uroporphyrinogen III or uroporphyrinogen I) are decarboxylated by the enzyme uroporphyrinogen decarboxylase. These new products have methyl groups in place of the original acetate groups and are known as coproporphyrinogens. Coproporphyrinogen III is the most important intermediate in heme synthesis. Coproporphyrinogen III is transported back from the cytosol into the interior of the mitochondria, where two propionate residues are decarboxylated (via coproporphyrinogen-III oxidase), which results in vinyl substituents on the 2 pyrrole rings. The resulting product is called protoporphyrinogen IX. The protoporphyrinogen IX is then converted into protoporphyrin IX by another enzyme called protoporphyrinogen IX oxidase. The final reaction in heme synthesis also takes place within the mitochondria and involves the insertion of the iron atom into the ring system generating the molecule known heme b. The enzyme catalyzing this reaction is known as ferrochelatase. The largest repository of heme in the body is in red blood cells (RBCs). RBCs have a life span of about 120 days. When the RBCs have reached the end of their useful lifespan, the cells are engulfed by macrophages and their constituents recycled or disposed of. Heme is broken down when the heme ring is opened by the enzyme known as heme oxygenase, which is found in the endoplasmic reticulum of the macrophages. The oxidation process produces the linear tetrapyrrole biliverdin, ferric iron (Fe3+), and carbon monoxide (CO). The carbon monoxide (which is toxic) is eventually discharged through the lungs. In the next reaction, a second methylene group (located between rings III and IV of the porphyrin ring) is reduced by the enzyme known as biliverdin reductase, producing bilirubin. Bilirubin is significantly less extensively conjugated than biliverdin. This reduction causes a change in the colour of the molecule from blue-green (biliverdin) to yellow-red (bilirubin). In hepatocytes, bilirubin-UDP-glucuronyltransferase (bilirubin-UGT) adds two additional glucuronic acid molecules to bilirubin to produce the more water-soluble version of the molecule known as bilirubin diglucuronide. In most individuals, intestinal bilirubin is acted on by the gut bacteria to produce the final porphyrin products, urobilinogens and stercobilins. These are excreted in the feces. The stercobilins oxidize to form brownish pigments which lead to the characteristic brown colour found in normal feces. Some of the urobilinogen produced by the gut bacteria is reabsorbed and re-enters the circulation. These urobilinogens are converted into urobilins that are then excreted in the urine which cause the yellowish colour in urine.