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Related Concept Videos

Phase II Reactions: Glutathione Conjugation and Mercapturic Acid Formation01:22

Phase II Reactions: Glutathione Conjugation and Mercapturic Acid Formation

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Glutathione, a tripeptide made up of glutamate, cysteine, and glycine, is a critical player in the detoxification of drugs and xenobiotics via a process known as glutathione conjugation or mercapturic acid formation. This phase II biotransformation reaction involves the covalent binding of glutathione to a drug or its metabolite, enhancing the compound's water solubility and enabling its excretion.
Several distinctive characteristics distinguish glutathione conjugation from other phase II...
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Oxidation of Phenols to Quinones01:17

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In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox...
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Phase II Reactions: Miscellaneous Conjugation Reactions01:19

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Phase II biotransformations are detoxification mechanisms that conjugate xenobiotics with endogenous substances, neutralizing their toxicity.
A key example involves the conjugation of cyanide ions, which impair cellular respiration and alter hemoglobin into non-oxygen-carrying cyanmethemoglobin. To neutralize this threat, a sulfur atom from thiosulphate is transferred to the cyanide ion, catalyzed by the enzyme rhodanese, resulting in an inactive compound called thiocyanate. The production of...
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Phase II Reactions: Sulfation and Conjugation with α-Amino Acids01:19

Phase II Reactions: Sulfation and Conjugation with α-Amino Acids

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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...
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Sulfur Assimilation01:20

Sulfur Assimilation

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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...
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Related Experiment Video

Updated: Jun 11, 2025

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry
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Fast and Selective Cysteine Conjugation Using para-Quinone Methides.

Ruimin Zhang1, Bo Li1, Liuli Dong1

  • 1School of Pharmacy, China Pharmaceutical University, Nanjing 211198, P. R. China.

Organic Letters
|October 7, 2024
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Summary

A new cysteine conjugation method uses para-quinone methides (p-QMs) for efficient and selective labeling. This technique successfully tagged a HER2 nanobody for targeted cancer cell imaging.

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Area of Science:

  • Chemical Biology
  • Organic Chemistry
  • Bioconjugation Chemistry

Background:

  • Cysteine conjugation is crucial for bioconjugation and drug development.
  • Existing methods may lack selectivity or efficiency.
  • Development of novel conjugation strategies is needed.

Purpose of the Study:

  • To develop an efficient and selective method for cysteine conjugation.
  • To utilize para-quinone methides (p-QMs) for bioconjugation.
  • To demonstrate the utility of p-QM conjugation in biological applications.

Main Methods:

  • Investigated the reactivity of p-QMs with amino acid derivatives, peptides, and proteins.
  • Determined reaction kinetics for p-QM-cysteine conjugation.
  • Applied p-QM conjugation to label a HER2 nanobody with a fluorescent probe.

Main Results:

  • p-QMs demonstrated high specificity for the cysteine residue.
  • p-QM-cysteine reactions exhibited robust kinetics (rate constants up to 1.67 × 10^4 M^-1·s^-1).
  • Successfully achieved selective labeling of HER2-positive SK-BR-3 cells using a p-QM-conjugated HER2 nanobody.

Conclusions:

  • p-QMs provide an efficient and selective method for cysteine conjugation.
  • This method offers a valuable tool for bioconjugation and targeted labeling applications.
  • The developed p-QM conjugation strategy shows promise for imaging and therapeutic applications.