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Related Concept Videos

Carrier-Mediated Transport01:06

Carrier-Mediated Transport

Carrier-mediated transport is a pivotal process in drug absorption, particularly for lipid-insoluble drugs, and encompasses facilitated diffusion and active transport. Facilitated diffusion allows drugs to move along their concentration gradient without energy expenditure, while active transport utilizes ATP to drive drug movement against this gradient.
Active transport involves two types of membrane-spanning transporters: uptake and efflux. Uptake transporters are expressed in the small...
Membrane Asymmetry Regulating Transporters01:19

Membrane Asymmetry Regulating Transporters

Enzymes like flippase, floppase, and scramblase transfer phospholipids from one layer to another in the membrane, thereby affecting membrane asymmetry.
Flippase
Eukaryotic flippases are type-IV P-type ATPases or P4-ATPases belonging to P-type ATPase family proteins that are membrane-bound pumps involved in the ATP-mediated transport of ions and molecules across the membrane. Flippases flip specific phospholipids from the outer to the inner leaflet of a membrane. All P4-ATPases have one...
Facilitated Diffusion01:16

Facilitated Diffusion

The plasma membrane, a critical structure in cellular biology, houses an array of transporters, or carrier proteins, interspersed within its lipid bilayer. These proteins play a crucial role in solute transport through facilitated diffusion, a form of passive diffusion that uses transporters to move the molecules across the membrane.
In this process, substrates such as organic compounds and ions interact with a transporter on one side, triggering conformational changes in proteins that enable...
ABC Transporters: Exporter01:31

ABC Transporters: Exporter

ATP-binding cassette or ABC transporter is the largest superfamily of integral membrane proteins. The transporters have transmembrane-binding domains (TMDs) and nucleotide-binding domains (NBDs). The TMDs are specific to their substrates, whereas the NBDs are similar to engines that complete ATP hydrolysis to complete the substrate transport. They can be full transporters consisting of two TMDs and NBDs, half transporters with one TMD and NBD, while some encoded with a single TMD or NBD are...
Drug Absorption Mechanism: Carrier-Mediated Membrane Transport01:19

Drug Absorption Mechanism: Carrier-Mediated Membrane Transport

Certain large, lipid-insoluble drug molecules that resemble amino acids, peptides, or glucose, require specialized carrier proteins to facilitate their diffusion across cell membranes. This transport can occur through either facilitated diffusion, which does not require energy input, or active transport, which does require energy input.
Facilitated diffusion is a passive process that utilizes human Solute Carrier (SLC) transporters. These transporters bind to the drug, undergo structural...
Active Transport01:14

Active Transport

Active transport is a critical biological process that allows cells to move solutes against an electrochemical gradient. This process requires direct energy input and is characterized by its selectivity, saturability, and susceptibility to competitive inhibition.
Primary active transporters, like Na+, K+ and -ATPase, directly utilize ATP to move ions across the membrane. These transporters play significant roles in various physiological processes. For instance, Na+, K+ and -ATPase maintain...

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Related Experiment Video

Updated: Jun 22, 2026

A Rapid and Specific Microplate Assay for the Determination of Intra- and Extracellular Ascorbate in Cultured Cells
11:56

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

Published on: April 11, 2014

Ascorbate and plasma membrane electron transport--enzymes vs efflux.

Darius J R Lane1, Alfons Lawen

  • 1Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Melbourne, VIC 3800, Australia.

Free Radical Biology & Medicine
|June 9, 2009
PubMed
Summary

Transplasma membrane electron transport (tPMET) involves electron transfer across cell membranes. Recent findings reveal cellular ascorbate export as a key mechanism for this process, impacting cellular homeostasis.

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Last Updated: Jun 22, 2026

A Rapid and Specific Microplate Assay for the Determination of Intra- and Extracellular Ascorbate in Cultured Cells
11:56

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Published on: April 11, 2014

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Area of Science:

  • Cell Biology
  • Biochemistry
  • Physiology

Background:

  • Transplasma membrane electron transport (tPMET) facilitates electron transfer across the plasma membrane, utilizing intracellular reductants like NADH and ascorbate to reduce extracellular oxidants.
  • Mammalian tPMET systems primarily use ascorbate as the proximal electron donor, traditionally viewed as an intracellular substrate for transmembrane enzymatic activity.
  • Candidate proteins for enzymatic tPMET include cytochrome b(561) family members, such as duodenal cytochrome b.

Purpose of the Study:

  • To explore the emerging evidence for cellular ascorbate export as a significant component of ascorbate-dependent tPMET.
  • To discuss the physiological relevance and implications of ascorbate release from cells.
  • To highlight the dual nature of ascorbate-dependent tPMET, encompassing both enzymatic and non-enzymatic (export-mediated) pathways.

Main Methods:

  • Review and synthesis of existing literature on transplasma membrane electron transport and ascorbate metabolism.
  • Analysis of evidence supporting cellular ascorbate export and dehydroascorbate import as mechanisms of tPMET.
  • Discussion of potential cellular pathways involved in ascorbate release, such as volume-sensitive anion channels and exocytosis.

Main Results:

  • Cellular export of ascorbate, coupled with dehydroascorbate import, represents a physiologically relevant pathway for ascorbate-dependent tPMET.
  • This export mechanism results in net electron transfer from the cytoplasm to the extracellular space, similar to enzymatic tPMET.
  • The precise mechanisms of cellular ascorbate release remain under investigation, with volume-sensitive anion channels and exocytosis as leading candidates.

Conclusions:

  • Ascorbate-dependent tPMET exhibits a "duality," involving both intracellular enzymatic transfer and extracellular release of ascorbate.
  • Cellular ascorbate release plays a crucial role in maintaining ascorbate levels in vital tissues like the blood and brain.
  • This pathway is implicated in cellular processes such as the uptake of non-transferrin-bound iron.