Name: sulfur uptake and cysteine synthesis
Uploaded: 2025-06-12T09:37:55.000Z
Duration: 1 min 20 s
Channel: JoVE

Lo zolfo è essenziale per sintetizzare gli amminoacidi, come la cisteina e la metionina, e i coenzimi, come il coenzima A e la biotina. I microrganismi assorbono lo zolfo principalmente sotto forma di solfati dal suolo e dall'acqua. Poiché il solfato è altamente ossidato, deve subire il processo di riduzione assimilatoria dello zolfo prima di essere incorporato nelle biomolecole. Questo processo inizia con l'attivazione del solfato, catalizzato dall'ATP solfurilasi, che forma l'adenosina-5-fosfosolfato. Questo è fosforilato in 3-fosfoadenosina-5-fosfossolfato o PAPS. PAPS rilascia solfito, che viene ulteriormente ridotto a idrogeno solforato dalla solfito reduttasi. Nei funghi, l'idrogeno solforato si combina con la serina per formare la cistina, che viene successivamente ridotta a cisteina. Nei batteri e in alcuni archei, l'idrogeno solforato si combina con l'O-acetilserina o l'O-fosfoserina per formare la cisteina. Una volta formata, la cisteina fornisce zolfo per la sintesi della metionina e di altri composti contenenti zolfo, come il coenzima A e la biotina.

assimilazione dello zolfo

Sulfur Assimilation

Lo zolfo &#232; un elemento essenziale nei sistemi biologici, partecipa alla sintesi di biomolecole chiave, tra cui aminoacidi come la cisteina e la metionina, e cofattori come il coenzima A e la biotina. I microrganismi assimilano lo zolfo principalmente sotto forma di solfato (SO_4^2-) proveniente dall&#8217;ambiente, che deve subire una serie di trasformazioni biochimiche prima di poter essere incorporato nei componenti cellulari. Visto che il solfato &#232; altamente ossidato, deve essere sottoposto a riduzione assimilativa per diventare biologicamente utilizzabile. Alcuni microrganismi possono utilizzare amminoacidi contenenti zolfo (cisteina, metionina) o composti di zolfo ridotto (tiosolfato, zolfo elementare) come fonti alternative di zolfo. Questi composti aggirano la necessit&#224; di attivazione e riduzione del solfato, consentendo un&#8217;assimilazione dello zolfo pi&#249; efficiente dal punto di vista energetico.
Via di attivazione e riduzione del solfato
Il processo inizia con l&#8217;attivazione del solfato da parte dell&#8217;ATP sulfurilasi, un enzima che catalizza la formazione di adenosina-5&#8242;-fosfosolfato (APS). L&#8217;APS agisce come intermedio chiave nel metabolismo del solfato, subendo una successiva fosforilazione per formare fosfoadenosina-5&#8242;-fosfosolfato (PAPS) oppure procedendo direttamente alla riduzione in alcuni batteri. Il PAPS &#232; fondamentale non solo per l&#8217;assimilazione del solfato, ma anche per le reazioni di solfatazione nei processi cellulari.
La riduzione del PAPS a solfito (SO_3^2-) avviene tramite la PAPS reduttasi, seguita dalla conversione del solfito a solfuro di idrogeno (H_2S) attraverso la solfito reduttasi. Queste riduzioni sequenziali convertono lo zolfo in una forma biologicamente accessibile per la sintesi di molecole organiche. Equivalenti riducenti, come il NADPH, forniscono elettroni per facilitare tali reazioni.
Incorporazione del solfuro di idrogeno nella cisteina
La fase finale dell&#8217;assimilazione dello zolfo coinvolge l&#8217;incorporazione del solfuro di idrogeno nel metabolismo degli amminoacidi. Nei funghi, l&#8217;H_2S reagisce con la serina per formare la cisteina. Nei batteri e in alcuni archaea, l&#8217;H_2S si combina con O-acetilserina o O-fosfoserina per formare cisteina tramite vie enzimatiche. L&#8217;O-acetilserina &#232; pi&#249; comunemente utilizzata nell&#8217;Escherichia coli e in batteri affini, mentre le vie dipendenti da O-fosfoserina sono presenti in alcuni archaea, come il Methanocaldococcus jannaschii.
La cisteina &#232; un precursore fondamentale per la biosintesi della metionina e per la produzione di cofattori contenenti zolfo come il coenzima A e la biotina. Inoltre, il metabolismo dello zolfo svolge un ruolo importante nell&#8217;omeostasi redox, in particolare attraverso la sintesi del glutatione, che protegge le cellule dallo stress ossidativo.

Assimilazione dello zolfo

Lo zolfo &#232; un elemento essenziale nei sistemi biologici, partecipa alla sintesi di biomolecole chiave, tra cui aminoacidi come la cisteina e la ...

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Microbial Metabolism

Metabolismo microbico

KEY TERMS AND CONCEPTS

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sulfur uptake and cysteine synthesis

Sulfur uptake and cysteine synthesis are key parts of microbial metabolism. Sulfur is needed to build important biomolecules, including the amino acids cysteine and methionine, as well as cofactors such as coenzyme A and biotin. Microorganisms usually take in sulfur from the environment as sulfate, but sulfate must be changed before cells can use it.

Because sulfate is highly oxidized, it must go through assimilatory sulfate reduction to become biologically useful. Some microorganisms can also use sulfur-containing amino acids like cysteine and methionine, or reduced sulfur compounds such as thiosulfate and elemental sulfur. These sources bypass sulfate activation and reduction, so they provide a more energy-efficient route for sulfur assimilation.

The pathway starts when ATP sulfurylase activates sulfate and forms adenosine-5′-phosphosulfate, or APS. APS is an important intermediate in sulfate metabolism. In some bacteria, it is reduced directly, while in others it is first phosphorylated to phosphoadenosine-5′-phosphosulfate, or PAPS. PAPS also has a role in sulfation reactions inside cells.

PAPS reductase converts PAPS to sulfite, and sulfite reductase then reduces sulfite to hydrogen sulfide, or H2S. These steps use reducing equivalents such as NADPH to provide electrons. The sequence of reductions turns sulfur into a form that cells can build into organic molecules.

The final step is the use of hydrogen sulfide in amino acid metabolism. In fungi, H2S reacts with serine to form cysteine. In bacteria and some archaea, H2S combines with O-acetylserine or O-phosphoserine to make cysteine. O-acetylserine is common in Escherichia coli and related bacteria, while O-phosphoserine pathways occur in some archaea, including Methanocaldococcus jannaschii.

Cysteine then helps make methionine and sulfur-containing cofactors such as coenzyme A and biotin. Sulfur metabolism also supports redox balance through glutathione synthesis. Glutathione helps protect cells from oxidative stress.

Sulfur Uptake and Cysteine Synthesis

microbial nutrition

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atp and energy production

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redox reactions

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introduction to metabolism

Metabolism: Energy Use and Biomolecule Synthesis

Metabolism is the set of chemical reactions that keep living cells working. It includes reactions that break down biomolecules and reactions that build them up. These two sides of metabolism work together to support energy balance and cell function. Catabolic pathways break large molecules into smaller parts. Carbohydrates, lipids, and proteins can be broken down into monosaccharides, fatty acids, and amino acids. These reactions release energy, and cells store much of that energy as ATP, or...

carbohydrate catabolism

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glycolysis

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Pentose Phosphate Pathway and Entner-Doudoroff

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electron transport chain components

Electron Transport Chain and ATP Production

The electron transport chain helps cells make ATP by moving electrons through membrane protein complexes. In eukaryotic cells, it sits in the inner mitochondrial membrane. In prokaryotic cells, it is found in the plasma membrane and can differ in the number and type of complexes, depending on the organism and its environment. The chain uses several electron carriers to pass electrons along in redox reactions, which are reactions that involve oxidation and reduction. These carriers include...

chemiosmosis and atp synthesis

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respiration pathways

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microbial fermentation

Fermentation Products in Microbes

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metabolism of chemolithotrophs

How Chemolithotrophs Make ATP

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amino acid catabolism

Microbes Use Proteins for Energy

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lipid catabolism

How Microbes Break Down Fats for Energy

Microbes break down triglycerides and fatty acids to make energy. Triglycerides are important long-term energy storage molecules in microorganisms. Lipases hydrolyze, or split with water, triglycerides into glycerol and free fatty acids. Each product then enters a different metabolic route that helps the cell make ATP, the main energy currency. Glycerol metabolism begins after glycerol is released from triglyceride hydrolysis. Glycerol kinase adds a phosphate group to form glycerol-3-phosphate.

oxygenic photosynthesis

How Plants Make Oxygen and ATP

Oxygenic photosynthesis is the process plants, algae, and cyanobacteria use to capture light energy and turn it into chemical energy. It uses water as the source of electrons and releases molecular oxygen, or O2. The process also produces ATP and NADPH, which cells need for later energy use and carbon fixation. The main reactions happen in the thylakoid membranes, where chlorophyll pigments absorb light. In cyanobacteria, these membranes come from folds in the plasma membrane. Two photosystems...

anoxygenic photosynthesis

Bacterial Light Capture Without Oxygen

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biosynthesis in bacteria

How Bacteria Build Key Macromolecules

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carbon-dioxide fixation

Microbial Carbon Fixation Pathways

Microbial carbon fixation pathways let prokaryotes turn carbon dioxide into organic molecules. This process supports biosynthesis, helps sustain ecosystems, and plays a role in the global carbon cycle. It also has industrial uses in carbon capture and bioproduct synthesis. Autotrophic organisms depend on this process to use CO2 as a carbon source in many environments. The Calvin cycle is the most common carbon fixation pathway. Cyanobacteria and other autotrophic prokaryotes use it, and it...

biosynthesis of polysaccharides

Activated Sugars for Polysaccharide Synthesis

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inorganic nitrogen assimilation

Nitrogen Uptake by Microbes

Nitrogen uptake by microbes is essential for making proteins, nucleic acids, and other cell parts. Many bacteria and archaea take in nitrogen as nitrate or ammonia. They then convert it into forms that can be built into biomolecules. When nitrate enters a cell, it goes through assimilatory nitrate reduction. This is a two-step process. First, nitrate reductase changes nitrate to nitrite using NADH or FAD as an electron donor, depending on environmental and cellular conditions. Then nitrite...

sulfur assimilation

Sulfur uptake and cysteine synthesis are key parts of microbial metabolism. Sulfur is needed to build important biomolecules, including the amino acids cysteine and methionine, as well as cofactors such as coenzyme A and biotin. Microorganisms usually take in sulfur from the environment as sulfate, but sulfate must be changed before cells can use it. Because sulfate is highly oxidized, it must go through assimilatory sulfate reduction to become biologically useful. Some microorganisms can also...

amino acid biosynthetic pathways

Amino Acid Building from Cell Metabolites

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biosynthesis of nucleic acids

Nucleotide Building Blocks for DNA and RNA

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biosynthesis of lipids

How Membrane Lipids Vary Across Life

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Lipopolysaccharides and Gram-Negative Defense

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key terms and concepts

Learn how microbes activate sulfate, reduce it to hydrogen sulfide, and use it to make cysteine, methionine, and sulfur-containing cofactors.

Sulfur Uptake and Cysteine Synthesis | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Sulfur Uptake and Cysteine Synthesis

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