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

O enxofre é essencial para sintetizar aminoácidos, como cisteína e metionina, e coenzimas, como coenzima A e biotina. Os microrganismos absorvem enxofre principalmente na forma de sulfatos do solo e da água. Como o sulfato é altamente oxidado, ele deve passar pelo processo de redução assimilatória de enxofre antes de ser incorporado às biomoléculas. Este processo começa com a ativação do sulfato, catalisado pela ATP sulfurilase, formando adenosina-5-fosfossulfato. Este é fosforilado em 3-fosfoadenosina-5-fosfossulfato ou PAPS. O PAPS libera sulfito, que é ainda mais reduzido a sulfeto de hidrogênio pela sulfito redutase. Nos fungos, o sulfeto de hidrogênio se combina com a serina para formar cistina, que mais tarde é reduzida a cisteína. Em bactérias e algumas archaea, o sulfeto de hidrogênio se combina com O-acetilserina ou O-fosfosserina para formar cisteína. Uma vez formada, a cisteína fornece enxofre para a síntese de metionina e outros compostos contendo enxofre, como a coenzima A e a biotina.

assimilação de enxofre

Sulfur Assimilation

O enxofre &#233; um elemento essencial nos sistemas biol&#243;gicos, contribuindo para a s&#237;ntese de biomol&#233;culas fundamentais, incluindo amino&#225;cidos como a ciste&#237;na e a metionina, e cofatores como a coenzima A e a biotina. Os microrganismos assimilam principalmente o enxofre na forma de sulfato (SO_4^2-) proveniente do ambiente, que deve passar por uma s&#233;rie de transforma&#231;&#245;es bioqu&#237;micas antes de ser incorporado aos componentes celulares. Como o sulfato &#233; altamente oxidado, deve ser submetido &#224; redu&#231;&#227;o assimilat&#243;ria de sulfato para se tornar biologicamente utiliz&#225;vel. Alguns microrganismos podem utilizar amino&#225;cidos contendo enxofre (ciste&#237;na, metionina) ou compostos sulfurados reduzidos (tiossulfato, enxofre elementar) como fontes alternativas de enxofre. Esses compostos evitam a necessidade de ativa&#231;&#227;o e redu&#231;&#227;o do sulfato, permitindo uma assimila&#231;&#227;o de enxofre energeticamente mais eficiente.
Via de Ativa&#231;&#227;o e Redu&#231;&#227;o do Sulfato
O processo inicia-se com a ativa&#231;&#227;o do sulfato pela enzima ATP sulfurilase, que catalisa a forma&#231;&#227;o de adenosina-5&#8242;-fosfossulfato (APS). O APS atua como um intermedi&#225;rio-chave no metabolismo do sulfato, podendo ser fosforilado posteriormente para formar fosfoadenosina-5&#8242;-fosfossulfato (PAPS) ou seguir diretamente para a redu&#231;&#227;o em algumas bact&#233;rias. O PAPS &#233; crucial n&#227;o apenas para a assimila&#231;&#227;o do sulfato, mas tamb&#233;m para rea&#231;&#245;es de sulfata&#231;&#227;o em processos celulares.
A redu&#231;&#227;o do PAPS a sulfito (SO_3^2-) ocorre por a&#231;&#227;o da PAPS redutase, seguida da convers&#227;o do sulfito em sulfeto de hidrog&#234;nio (H_2S) atrav&#233;s da sulfito redutase. Essas redu&#231;&#245;es sequenciais convertem o enxofre em uma forma biologicamente acess&#237;vel para a incorpora&#231;&#227;o em mol&#233;culas org&#226;nicas. Equivalentes redutores, como o NADPH, doam el&#233;trons para viabilizar as convers&#245;es nessas rea&#231;&#245;es.
Incorpora&#231;&#227;o do Sulfeto de Hidrog&#234;nio na Ciste&#237;na
A etapa final da assimila&#231;&#227;o de enxofre envolve a incorpora&#231;&#227;o do sulfeto de hidrog&#234;nio no metabolismo de amino&#225;cidos. Em fungos, o H_2S reage com a serina para formar ciste&#237;na. Em bact&#233;rias e algumas arqueias, o H_2S combina-se com O-acetilserina ou O-fosfoserina para formar ciste&#237;na por meio de vias enzim&#225;ticas. A O-acetilserina &#233; mais comumente utilizada em Escherichia coli e bact&#233;rias relacionadas, enquanto vias dependentes de O-fosfoserina s&#227;o encontradas em determinadas arqueias, como Methanocaldococcus jannaschii.
A ciste&#237;na &#233; um precursor chave na bioss&#237;ntese de metionina e na produ&#231;&#227;o de cofatores contendo enxofre, como a coenzima A e a biotina. Al&#233;m disso, o metabolismo do enxofre desempenha um papel na homeostase redox, particularmente por meio da s&#237;ntese de glutationa, que protege as c&#233;lulas contra o estresse oxidativo.

Assimilação de Enxofre

O enxofre &#233; um elemento essencial nos sistemas biol&#243;gicos, contribuindo para a s&#237;ntese de biomol&#233;culas fundamentais, incluindo ...

Education

JoVE Core

Microbiology

Microbiologia

Unit

Unidade

Microbial Metabolism

Metabolismo Microbiano

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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

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How Plants Make Oxygen and ATP

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inorganic nitrogen assimilation

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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...

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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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