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Related Concept Videos

Sulfur Assimilation01:20

Sulfur Assimilation

Sulfur is an essential element in biological systems, contributing to synthesizing key biomolecules, including amino acids such as cysteine and methionine, and cofactors such as coenzyme A and biotin. Microorganisms primarily assimilate sulfur as sulfate (SO₄²⁻) from the environment, which must undergo a series of biochemical transformations before it can be incorporated into cellular components. As sulfate is highly oxidized, it must undergo assimilatory sulfate reduction to become...
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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
Phase II Reactions: Sulfation and Conjugation with α-Amino Acids01:19

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Sulfation and α-amino acid conjugation are two critical biotransformation reactions in drug metabolism. Sulfation, a phase II biotransformation reaction, involves adding a polar sulfate group to a drug, enhancing its water solubility and promoting excretion. This process can either co-occur with or occur independently of glucuronidation. Nonmicrosomal sulfotransferase enzymes catalyze the process. The reaction involves 3'-phosphoadenosine-5'-phosphosulfate or PAPS coenzyme activation, sulfur...
Acid Mine Drainage01:19

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Mining activities that disturb sulfide-rich rocks, particularly those containing pyrite (FeS₂), initiate a cascade of geochemical and microbiological processes with serious environmental implications. When exposed to air and water, pyrite undergoes oxidation, releasing sulfate, ultimately forming sulfuric acid and mobilizing heavy metals into surrounding water systems. This phenomenon, known as acid mine drainage (AMD), results in low pH waters laden with toxic elements that threaten aquatic...
Phase I Reactions: Reductive Reactions01:27

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Phase I biotransformation reductive reactions are chemical processes that modify drugs by introducing or revealing polar functional groups via reduction. Enzymes called reductases catalyze these reactions, playing a pivotal role in drug metabolism by transforming lipophilic drugs into more polar, water-soluble metabolites for easy excretion. An essential type of reductive reaction is the carbonyl group reduction, where aldehydes and ketones are reduced to alcohols. An example is the...

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Updated: Jun 10, 2026

Experimental Column Setup for Studying Anaerobic Biogeochemical Interactions Between Iron (Oxy)Hydroxides, Trace Elements, and Bacteria
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Arsenolysis and thiol-dependent arsenate reduction.

David J Thomas1

  • 1Pharmacokinetics Branch, Integrated Systems Toxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, MD B143-1, 109 Alexander Drive, Research Triangle Park, North Carolina 27711, USA. thomas.david@epa.gov

Toxicological Sciences : an Official Journal of the Society of Toxicology
|July 28, 2010
PubMed
Summary

Arsenate is converted to arsenite, a key step in arsenic metabolism influencing toxicity. Thiol-dependent reduction of arsenate esters by enzymes may control this crucial cellular process.

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Area of Science:

  • Biochemistry
  • Environmental Toxicology
  • Metalloid Metabolism

Background:

  • Arsenate (As V) conversion to arsenite (As III) is a critical step in arsenic metabolism.
  • Methylated arsenic metabolites influence arsenic distribution, retention, reactivity, and toxicity.
  • Toxic and carcinogenic effects of arsenic exposure are likely mediated by methylated arsenicals.

Discussion:

  • Phosphorolytic-arsenolytic enzymes facilitate arsenate ester activation.
  • Thiol-dependent reduction of these activated esters yields arsenite.
  • This thiol-dependent reduction is a key reductive process controlling arsenic flux into methylation pathways.

Key Insights:

  • A biologically plausible mechanism for arsenate reduction involves enzyme-activated arsenate esters and thiol reductants.
  • This pathway is crucial for understanding cellular arsenic handling and toxicity.
  • The reduction of arsenate to arsenite is a central event in arsenic biotransformation.

Outlook:

  • Integrating reductive processes into a conceptual model of arsenic metabolism is needed.
  • Further research can elucidate the cellular machinery involved in arsenic biotransformation.
  • Understanding these pathways can inform strategies for mitigating arsenic toxicity.