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Related Concept Videos

Cofactors and Coenzymes01:27

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.
Cofactors and Coenzymes01:27

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.
Regulation of Metabolism01:19

Regulation of Metabolism

Cellular needs and conditions vary from cell to cell and change within individual cells over time. For example, the required enzymes and energetic demands of stomach cells are different from those of fat storage cells, skin cells, blood cells, and nerve cells. Furthermore, a digestive cell works much harder to process and break down nutrients during the time that closely follows a meal compared with many hours after a meal. As these cellular demands and conditions vary, so do the amounts and...
Introduction to Mechanisms of Enzyme Catalysis01:13

Introduction to Mechanisms of Enzyme Catalysis

For many years, scientists thought that enzyme-substrate binding took place in a simple "lock-and-key" fashion. This model stated that the enzyme and substrate fit together perfectly in one instantaneous step. However, current research supports a more refined view scientists call induced fit. The induced-fit model expands upon the lock-and-key model by describing a more dynamic interaction between enzyme and substrate. As the enzyme and substrate come together, their interaction causes a mild...
Cofactors and Coenzymes01:24

Cofactors and Coenzymes

Enzymes are proteins made of amino acids. The functional group of each constituent amino acid catalyzes a wide variety of chemical reactions via ionic interactions or acid-base reactions. However, amino acids cannot catalyze oxidation-reduction and group transfer reactions and need to be aided by non-protein components called cofactors. Cofactors are also referred to as the chemical teeth of an enzyme.
Cofactors can be metallic ions or organic molecules called coenzymes. These types of helper...
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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Updated: Jun 21, 2026

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09:00

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Published on: November 4, 2010

Naturally occurring auxin transport regulators.

M Jacobs, P H Rubery

    Science (New York, N.Y.)
    |July 15, 1988
    PubMed
    Summary

    Flavonoids like quercetin can bind to the naphthylphthalamic acid (NPA) receptor, inhibiting polar auxin transport in plants. These compounds may function as natural regulators of auxin transport.

    Area of Science:

    • Plant biology
    • Molecular plant physiology
    • Biochemistry

    Background:

    • Polar auxin transport is crucial for plant development and growth.
    • Synthetic compounds, such as naphthylphthalamic acid (NPA), inhibit auxin transport by binding to a specific receptor.
    • The endogenous ligand for the NPA receptor has not yet been identified.

    Purpose of the Study:

    • To investigate whether flavonoids can act as endogenous ligands for the NPA receptor.
    • To determine if flavonoids can modulate polar auxin transport in plants.

    Main Methods:

    • Competitive binding assays using radiolabeled NPA ([3H]NPA) and various flavonoids.
    • Experiments assessing the effect of flavonoids on auxin transport in different plant tissues and systems.

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    Main Results:

    • Specific flavonoids, including quercetin, apigenin, and kaempferol, competed with [3H]NPA for binding to the NPA receptor.
    • These flavonoids perturbed polar auxin transport in plant tissues, mimicking the effects of synthetic inhibitors.
    • The effective concentrations of flavonoids were in the micromolar range, consistent with likely endogenous levels.

    Conclusions:

    • Flavonoids are identified as potential endogenous ligands for the NPA receptor.
    • Flavonoids may play a natural role in regulating polar auxin transport in plants.
    • This finding provides a new perspective on the molecular mechanisms controlling auxin transport and plant development.