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

Schwefel ist essentiell für die Synthese von Aminosäuren wie Cystein und Methionin und Coenzymen wie Coenzym A und Biotin. Mikroorganismen nehmen Schwefel vor allem in Form von Sulfaten aus dem Boden und Wasser auf. Da Sulfat stark oxidiert ist, muss es den Prozess der assimilatorischen Schwefelreduktion durchlaufen, bevor es in Biomoleküle eingebaut wird. Dieser Prozess beginnt mit der Sulfataktivierung, die durch ATP-Sulfurylase katalysiert wird und Adenosin-5-phosphosulfat bildet. Dieses wird zu 3-Phosphoadenosin-5-phosphosulfat oder PAPS phosphoryliert. PAPS setzt Sulfit frei, das durch Sulfitreduktase weiter zu Schwefelwasserstoff reduziert wird. In Pilzen verbindet sich der Schwefelwasserstoff mit Serin zu Cystin, das später zu Cystein reduziert wird. In Bakterien und einigen Archaeen verbindet sich Schwefelwasserstoff entweder mit O-Acetylserin oder O-Phosphoserin zu Cystein. Einmal gebildet, liefert Cystein Schwefel für die Synthese von Methionin und anderen schwefelhaltigen Verbindungen wie Coenzym A und Biotin.

schwefelassimilation

Sulfur Assimilation

Schwefel ist ein essentielles Element in biologischen Systemen und tr&#228;gt zur Synthese wichtiger Biomolek&#252;le bei, darunter Aminos&#228;uren wie Cystein und Methionin sowie Kofaktoren wie Coenzym A und Biotin. Mikroorganismen assimilieren Schwefel haupts&#228;chlich in Form von Sulfat (SO_4^2-) aus der Umwelt, welches eine Reihe von biochemischen Umwandlungen durchlaufen muss, bevor es in zellul&#228;re Komponenten eingebaut werden kann. Da Sulfat stark oxidiert ist, muss es einer assimilatorischen Sulfatreduktion unterzogen werden, um biologisch nutzbar zu werden. Einige Mikroorganismen k&#246;nnen schwefelhaltige Aminos&#228;uren (Cystein, Methionin) oder reduzierte Schwefelverbindungen (Thiosulfat, elementarer Schwefel) als alternative Schwefelquellen nutzen. Diese Verbindungen umgehen die Notwendigkeit der Aktivierung und Reduktion des Sulfates, was eine energieeffizientere Schwefelassimilation erm&#246;glicht.
Stoffwechselweg der Sulfataktivierung und -reduktion
Der Prozess beginnt mit der Aktivierung von Sulfat durch die ATP-Sulfurylase, ein Enzym, das die Bildung von Adenosin-5-phosphosulfat (APS) katalysiert. APS dient als Schl&#252;sselmolek&#252;l im Sulfatstoffwechsel und wird entweder weiter zu Phosphoadenosin-5-phosphosulfat (PAPS) phosphoryliert oder direkt durch Reduktion weiterverarbeitet, wie es bei einigen Bakterien der Fall ist. PAPS ist nicht nur f&#252;r die Schwefelassimilation von Bedeutung, sondern auch f&#252;r die Sulfatierungen in zellul&#228;ren Prozessen.
Die Reduktion von PAPS zu Sulfit (SO_3^2-) erfolgt durch die PAPS-Reduktase, gefolgt von der Umwandlung von Sulfit zu Schwefelwasserstoff (H_2S) durch die Sulfit-Reduktase. Diese aufeinanderfolgenden Reduktionen machen Schwefel f&#252;r organische Molek&#252;le biologisch verf&#252;gbar. Reduktions&#228;quivalente wie NADPH spenden Elektronen, um die Umwandlungen in diesen Reaktionen zu erm&#246;glichen.
Einbau von Schwefelwasserstoff in Cystein
Der letzte Schritt der Schwefelassimilation beinhaltet den Einbau von Schwefelwasserstoff in den Aminos&#228;urestoffwechsel. Bei Pilzen reagiert H_2S mit Serin zu Cystein. Bei Bakterien und einigen Archaeen verbindet sich H_2S entweder mit O-Acetylserin oder O-Phosphoserin um &#252;ber enzymatische Wege Cystein zu bilden. O-Acetylserin wird h&#228;ufiger von Escherichia coli und verwandten Bakterien verwendet, w&#228;hrend von O-Phosphoserin abh&#228;ngige Stoffwechselwege in bestimmten Archaeen wie Methanocaldococcus jannaschii vorkommen.
Cystein ist ein wichtiger Vorl&#228;ufer f&#252;r die Methioninbiosynthese und die Produktion schwefelhaltiger Kofaktoren wie Coenzym A und Biotin. Dar&#252;ber hinaus spielt der Schwefelstoffwechsel eine Rolle bei der Redox-Hom&#246;ostase, insbesondere durch die Synthese von Glutathion, das die Zellen vor oxidativem Stress sch&#252;tzt.

Schwefelassimilation

Schwefel ist ein essentielles Element in biologischen Systemen und tr&#228;gt zur Synthese wichtiger Biomolek&#252;le bei, darunter Aminos&#228;uren wie ...

Education

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JoVE Core

Microbiology

Mikrobiologie

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Microbial Metabolism

Mikrobieller Stoffwechsel

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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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introduction to metabolism

Metabolism: Energy Use and Biomolecule Synthesis

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electron transport chain components

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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

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oxygenic photosynthesis

How Plants Make Oxygen and ATP

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Bacterial Light Capture Without Oxygen

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carbon-dioxide fixation

Microbial Carbon Fixation Pathways

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biosynthesis of polysaccharides

Activated Sugars for Polysaccharide Synthesis

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inorganic nitrogen assimilation

Nitrogen Uptake by Microbes

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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

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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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