a precursor of heme and chlorophyll biosynthesis
Proteins are made of 20 different amino acids, DNA and RNA are made of 4 different types of nucleotides.
a precursor of heme and chlorophyll biosynthesis.
An alternative route for haem b biosynthesis is operative in sulphate-reducing bacteria of the Desulfovibrio genus and in methanogenic Archaea. This pathway diverges from the canonical one at the level of uroporphyrinogen III and progresses via a distinct branch, where sirohaem acts as an intermediate precursor being converted into haem b by a set of novel enzymes, named the alternative haem biosynthetic proteins (Ahb). In this work, we report the biochemical characterisation of the Desulfovibrio vulgaris AhbD enzyme that catalyses the last step of the pathway. Mass spectrometry analysis showed that AhbD promotes the cleavage of S-adenosylmethionine (SAM) and converts iron-coproporphyrin III via two oxidative decarboxylations to yield haem b, methionine and the 5'-deoxyadenosyl radical. Electron paramagnetic resonance spectroscopy studies demonstrated that AhbD contains two [4Fe-4S](2+/1+) centres and that binding of the substrates S-adenosylmethionine and iron-coproporphyrin III induces conformational modifications in both centres. Amino acid sequence comparisons indicated that D. vulgaris AhbD belongs to the radical SAM protein superfamily, with a GGE-like motif and two cysteine-rich sequences typical for ligation of SAM molecules and iron-sulphur clusters, respectively. A structural model of D. vulgaris AhbD with putative binding pockets for the iron-sulphur centres and the substrates SAM and iron-coproporphyrin III is discussed.
Hemes (a, b, c, and o) and heme d 1 belong to the group of modified tetrapyrroles, which also includes chlorophylls, cobalamins, coenzyme F430, and siroheme. These compounds are found throughout all domains of life and are involved in a variety of essential biological processes ranging from photosynthesis to methanogenesis. The biosynthesis of heme b has been well studied in many organisms, but in sulfate-reducing bacteria and archaea, the pathway has remained a mystery, as many of the enzymes involved in these characterized steps are absent. The heme pathway in most organisms proceeds from the cyclic precursor of all modified tetrapyrroles uroporphyrinogen III, to coproporphyrinogen III, which is followed by oxidation of the ring and finally iron insertion. Sulfate-reducing bacteria and some archaea lack the genetic information necessary to convert uroporphyrinogen III to heme along the "classical" route and instead use an "alternative" pathway. Biosynthesis of the isobacteriochlorin heme d 1, a cofactor of the dissimilatory nitrite reductase cytochrome cd 1, has also been a subject of much research, although the biosynthetic pathway and its intermediates have evaded discovery for quite some time. This review focuses on the recent advances in the understanding of these two pathways and their surprisingly close relationship via the unlikely intermediate siroheme, which is also a cofactor of sulfite and nitrite reductases in many organisms. The evolutionary questions raised by this discovery will also be discussed along with the potential regulation required by organisms with overlapping tetrapyrrole biosynthesis pathways.
Mosaic Origin of the Heme Biosynthesis Pathway in …
Modified tetrapyrroles such as chlorophyll, heme, siroheme, vitamin B(12), coenzyme F(430), and heme d(1) underpin a wide range of essential biological functions in all domains of life, and it is therefore surprising that the syntheses of many of these life pigments remain poorly understood. It is known that the construction of the central molecular framework of modified tetrapyrroles is mediated via a common, core pathway. Herein a further branch of the modified tetrapyrrole biosynthesis pathway is described in denitrifying and sulfate-reducing bacteria as well as the Archaea. This process entails the hijacking of siroheme, the prosthetic group of sulfite and nitrite reductase, and its processing into heme and d(1) heme. The initial step in these transformations involves the decarboxylation of siroheme to give didecarboxysiroheme. For d(1) heme synthesis this intermediate has to undergo the replacement of two propionate side chains with oxygen functionalities and the introduction of a double bond into a further peripheral side chain. For heme synthesis didecarboxysiroheme is converted into Fe-coproporphyrin by oxidative loss of two acetic acid side chains. Fe-coproporphyrin is then transformed into heme by the oxidative decarboxylation of two propionate side chains. The mechanisms of these reactions are discussed and the evolutionary significance of another role for siroheme is examined.
Heme precursors in the blood, urine, or stool give some indication of the type of porphyria, but more detailed biochemical testing is required to determine their exact identity. Making this determination yields a strong indicator of which enzyme in the heme biosynthesis pathway is defective, which in turn allows a diagnosis of the particular type of porphyria.
Chapter 21 : Biosynthesis of Amino Acids, Nucleotides, …
Hematin— A drug that is administered intravenously to halt an acute porphyria attack. It inhibits heme biosynthesis, preventing the further accumulation of heme precursors.
When an attack occurs, medical attention is needed. Pain is usually severe, and narcotic analgesics are the best option for relief. Phenothiazines can be used to counter nausea, vomiting, and anxiety; and chloral hydrate or diazepam is useful for sedation or to induce sleep. Intravenously administered hematin may be used to curtail an attack. This drug seems to work by signaling the heme biosynthesis pathway to slow production of precursors. Women, who tend to develop symptoms more frequently than men in response to hormonal fluctuations, may find hormone therapy that inhibits ovulation to be helpful.
Lect 39 Amino Acid Biosynthesis - University of Arizona
Overview of amino acid biosynthesis
Glutamyl-transfer RNA: a precursor of heme and chlorophyll biosynthesis
Glutamyl-transfer RNA: a precursor of heme and …
Mosaic Origin of the Heme Biosynthesis Pathway in Photosynthetic Eukaryotes Miroslav Oborník
The main characteristic of the porphyrias is a defect in one of the enzymes of the heme biosynthesis pathway
Trends in Biochemical Sciences All Journals
Biosynthesis of heme is a multistep process that starts with simple molecules and ends with a large, complex heme molecule. Each step of the biosynthesis pathway is directed by its own enzyme (a task-specific protein). As a heme precursor molecule moves through each step, an enzyme modifies it in some way. If the precursor is not modified, it cannot proceed to the next step.
Since the initial steps of heme biosynthesis differ ..
AB - Considering both the wide spread utilization of porphyrins as photodiagnostic and phototherapeutic agents for tumours, and the limited information about the heme biosynthetic pathway in neoplastic tissues, a study of porphyrin biosynthesis in human breast adenocarcinoma, determining first the optimal working conditions, was initiated. The effect of temperature, maintenance time and the amount of precursor (δ-aminolevulinic acid, ALA) added and uptaken by normal and neoplastic tissue on the formation of porphyrins was determined. The optimal initial ALA concentration was approximately 34 μg/ml, while optimal temperature and maintenance time were 37°C and 24 h respectively. Under these conditions, porphyrin biosynthesis in tumoral tissue was about five times higher than normal. The functionality of the heme enzymes was indirectly measured by means of porphyrin chromatographic separation. Starting with ALA as substrate it was shown that the heme biosynthetic pathway was functional in the neoplastic tissue, up to the formation of protoporphyrinogen.
Porphyrin and Heme Synthesis and Bilirubin Metabolism
The main characteristic of the porphyrias is a defect in one of the enzymes of the heme biosynthesis pathway. The defect prevents protoporphyrins or porphyrin (heme precursors) from proceeding further along the pathway. Symptoms may be debilitating or life-threatening in some cases. Porphyria is an inherited condition, but it may be acquired after exposure to poisonous substances.
Amino Acid Derivatives: Catecholamine, …
Although production is concentrated in the liver and bone marrow, heme is used in various capacities in virtually every tissue in the body. In most cells, it is a key building block in the construction of factors that oversee metabolism as well as transport of oxygen and energy. In immature red blood cells, heme is a featured component of hemoglobin. Hemoglobin is the red pigment that gives red blood cells the ability to transport oxygen as well as their characteristic color.
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