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Related Concept Videos

Pharmacogenetics of Phase II Enzymes: N-acetyltransferase, Thiopurine S-methyltransferase, UDP-glucuronosyltransferase01:27

Pharmacogenetics of Phase II Enzymes: N-acetyltransferase, Thiopurine S-methyltransferase, UDP-glucuronosyltransferase

Phase II biotransformation reactions are essential for detoxifying and eliminating xenobiotics, including many pharmaceutical compounds. These reactions typically involve conjugation, the covalent attachment of polar endogenous groups such as glucuronic acid, sulfate, methyl, or acetyl moieties to functional groups introduced during Phase I metabolism. The resulting conjugates are more water-soluble, enabling efficient renal or biliary excretion.The major classes of Phase II enzymes include...
Phase II Reactions: Glucuronidation01:24

Phase II Reactions: Glucuronidation

Glucuronidation, a pivotal phase II biotransformation process, involves the coupling of glucuronic acid to a drug or xenobiotic. Given its widespread occurrence and critical role in drug metabolism, it's considered the most crucial phase II reaction. It enhances the water solubility of substances, aiding their expulsion from the body. The driving force behind these reactions is a group of enzymes known as UDP-glucuronosyltransferases (UGTs). UGTs facilitate the transfer of a glucuronic acid...
Drug Metabolism: Phase II Reactions01:14

Drug Metabolism: Phase II Reactions

Phase II reactions are essential for the detoxification and elimination of drugs from the body. These reactions involve the conjugation of parent drugs or their phase I metabolites with endogenous molecules, resulting in more hydrophilic drug conjugates. The primary conjugation reactions in this phase are sulfation and glucuronidation. Both sulfation and glucuronidation typically produce biologically inactive metabolites. However, in some cases involving prodrugs, active metabolites may be...
Pharmacogenetics of Drug Targets: β₂-Adrenergic Receptors, Apo E, Thymidylate Synthase01:11

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Genetic polymorphisms in drug targets have emerged as critical determinants of interindividual variability in drug response and toxicity. Pharmacogenomic investigations increasingly focus on identifying these variations to personalize and optimize therapeutic interventions. A drug target may be a receptor, enzyme, or signaling protein involved in pharmacologic responses or disease-related pathways. While early pharmacogenetic studies focused primarily on drug metabolism, current research...
Testosterone: Functions and Regulation01:26

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The intricate hormonal interplay essential for male reproductive health begins with the release of gonadotropin-releasing hormone (GnRH) by the hypothalamus. This hormone prompts the pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). LH targets the Leydig cells in the testes, stimulating them to produce and release testosterone. In concert with testosterone, FSH acts on the Sertoli cells within the seminiferous tubules to facilitate the release of...
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Pharmacogenetics of Phase I Enzymes: Cytochrome P450 Isozymes

Cytochrome P450 (CYP450) enzymes are a superfamily of heme-containing monooxygenases that play a pivotal role in Phase I drug metabolism by catalyzing oxidation and reduction reactions.These enzymes transform lipophilic xenobiotics into more hydrophilic metabolites, facilitating subsequent Phase II conjugation and eventual excretion. The CYP450 family is classified into families (e.g., CYP1–CYP3) and subfamilies (e.g., CYP2A, CYP2C), based on amino acid sequence homology.CYP450 isoenzymes,...

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Extremely Rapid and Specific Metabolic Labelling of RNA In Vivo with 4-Thiouracil (Ers4tU)
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Testosterone and epitestosterone differentially regulate UDP-glucuronosyltransferases (UGT) activity.

Ling Xiao1, Juan Qi2, Yuanyuan Zhang2

  • 1School of Resources and Environment, Anqing Normal University, Anqing 246311, China.

The Journal of Steroid Biochemistry and Molecular Biology
|June 16, 2026
PubMed
Summary
This summary is machine-generated.

Epitestosterone (epiT) significantly impacts UDP-glucuronosyltransferase (UGT) activity more than testosterone (T). This study reveals epiT as a potent endogenous modulator of glucuronidation in androgen-rich tissues.

Keywords:
Enzyme inhibitionEnzyme stimulationEpitestosterone (epiT)Testosterone (T)UDP-glucuronosyltransferases (UGT)

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Area of Science:

  • Biochemistry
  • Pharmacology
  • Molecular Biology

Background:

  • Endogenous substrates' effects on UDP-glucuronosyltransferase (UGT) activity are not well understood.
  • Testosterone (T) and epitestosterone (epiT) are endogenous substrates with potential roles in UGT modulation.

Purpose of the Study:

  • To investigate the in vitro and in silico effects of T and epiT on UGT activity.
  • To elucidate the mechanisms by which T and epiT modulate UGT enzymes.

Main Methods:

  • In vitro enzyme kinetics assays were performed for UGT inhibition and activation.
  • In silico molecular docking studies were used to predict binding interactions.
  • Kinetic models were applied to analyze enzyme activation by T and epiT.

Main Results:

  • Epitestosterone exhibited stronger competitive inhibition against UGT2B7 and UGT2B15 compared to testosterone.
  • Both T and epiT activated UGT2B17, with epiT showing a greater increase in turnover number.
  • Molecular docking indicated tighter binding of epiT to UGT2B7 and UGT2B15 due to additional hydrogen bonds.

Conclusions:

  • A single stereochemical inversion between T and epiT dramatically enhances UGT modulation.
  • Epitestosterone is identified as a significant endogenous modulator of glucuronidation in androgen-rich tissues.