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Related Concept Videos

Drug Metabolism: Phase I Reactions01:17

Drug Metabolism: Phase I Reactions

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A phase I reaction is a biochemical process that introduces a functionally reactive polar group to a substance. This transformation predominantly occurs in the liver, facilitated by the cytochrome P450 system of hemoproteins situated in the lipophilic endoplasmic reticulum of cells. The metabolite generated through this process can have varying polarities. If it is sufficiently polar, it can be easily excreted in the urine due to its water compatibility. However, if the metabolite is nonpolar,...
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Drug Metabolism: Phase II Reactions01:14

Drug Metabolism: Phase II Reactions

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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...
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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...
194
Phase II Reactions: Glucuronidation01:24

Phase II Reactions: Glucuronidation

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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...
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Bioavailability: Overview01:13

Bioavailability: Overview

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Bioavailability refers to the proportion of an unaltered drug that, after administration, enters the systemic circulation and can be distributed to the desired action site. Factors such as gastrointestinal (GI) absorption and liver biotransformation influence the bioavailability of a drug when it is administered orally. When a drug is administered intravenously, it enters the systemic circulation directly; by definition, its bioavailability is assumed to be 100%. The bioavailability of an...
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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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Related Experiment Video

Updated: Jun 27, 2025

A Rapid and Specific Microplate Assay for the Determination of Intra- and Extracellular Ascorbate in Cultured Cells
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A Rapid and Specific Microplate Assay for the Determination of Intra- and Extracellular Ascorbate in Cultured Cells

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Ascorbic acid metabolism and functions.

Patricia L Conklin1, Christine H Foyer2, Robert D Hancock3

  • 1Biological Sciences Department, Bowers Hall Rm 240, SUNY Cortland, Cortland, NY 13045, USA.

Journal of Experimental Botany
|May 3, 2024
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Summary
This summary is machine-generated.

This special issue celebrates 25 years of the Smirnoff-Wheeler pathway for plant ascorbate biosynthesis. It reviews current knowledge and future research directions for vitamin C metabolism and roles in plants.

Keywords:
l-galactose-galactose phosphorylaseAscorbic acidGDP-ascorbate oxidaseascorbate peroxidasedehydroascorbate reductaseglutathione reductasemannosemonodehydroascorbate reductaseoxalic acidredox signallingtartaric acidthreonic aciduORF

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Area of Science:

  • Plant biochemistry
  • Molecular biology
  • Plant physiology

Background:

  • Commemorating the 25th anniversary of the Smirnoff-Wheeler pathway for ascorbate biosynthesis in plants.
  • Assessing the current understanding of vitamin C metabolism in plant systems.

Discussion:

  • Exploring the intricate metabolic routes of ascorbate synthesis and breakdown.
  • Investigating the diverse physiological functions of ascorbate in plant growth and stress response.

Key Insights:

  • The Smirnoff-Wheeler pathway remains a cornerstone in understanding plant vitamin C production.
  • Ascorbate plays critical roles beyond its antioxidant function, influencing cell signaling and development.

Outlook:

  • Identifying knowledge gaps in ascorbate's complex roles within plants.
  • Charting future research trajectories for plant ascorbate metabolism and functional analysis.