API

Event: 1542

Key Event Title

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Mitochondrial Complex III inhibition

Short name

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Mitochondrial Complex III inhibition

Biological Context

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Level of Biological Organization
Molecular

Cell term

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Organ term

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Key Event Components

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Process Object Action

Key Event Overview


AOPs Including This Key Event

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AOP Name Role of event in AOP
Mitochondrial complex inhibition leading to liver injury MolecularInitiatingEvent
Complex III inhibition leading to mortality MolecularInitiatingEvent
Complex III inhibition leading to lethality MolecularInitiatingEvent

Stressors

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Taxonomic Applicability

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Life Stages

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Sex Applicability

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Key Event Description

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The mitochondrial complex III (mitochondrial cytochrome bc1 complex) is an enzyme complex located in the inner membrane of mitochondria. It is the third out of 5 complexes that together form the mitochondrial respiratory chain. It consists out of multiple subunits, including cytochrome b/b6, cytochrome c1 and an 2Fe-2S cluster.

The combination of these subunits catalyze following process:

  1. The cytochrome c1 is involved in the process of oxidizing ubiquinol (coming directly from complex I, from complex I via complex II or from complex II) to a semiquinone radical and back to quinone. A process that results in two free electrons that are transferred via cytochrome c to next complex.

 

The electron transfer in this process mediates the translocation of protons from the mitochondrial matrix through the inner membrane to the intermembrane space. The created proton gradient will be used to catalyze the reaction in which ADP is converted into ATP.

 

The initiation event is the reversibly or irreversibly interaction to any of the subunits in the mitochondrial complex III, leading to an perturbation of the electron flow and an absence of proton transport via this complex.


How It Is Measured or Detected

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Complex inhibition assays specifically for complex III
It is important to release that the activity of complex II depends on the input from complex II. So screening of effects at complex II is advised. The assay exist in multiple forms. Some assay can be performed on whole cells and other needed complex isolation based on antibody interactions. However, they all rely on the following detection of complex II/III activity:
The reduction of cytochrome c, which has an absorbance at 550nm.

Mitochondrial Membrane potential using fluorescent dyes.
Positive charged molecules will accumulated in the mitochondria in an inverse proportion as the membrane potential. More polarised mitochondria will accumulate more dye (Rhodamine123, TMRE, TMRM) - leading to a higher fluorescent signal - and the absence of membrane potential leads to an absence of fluorescent signal. An exception is the dye JC1, because this dye has green fluorescence when present in low concentrations (depolarisation) and red fluorescence when accumulated (hyperpolarized)

 

Measurements

Complex inhibition assays

  1. Cayman MitoCheck
    MitoCheck® Complex II/III Activity Assay Kit (Item No. 700950)

  2. Abcam
    MitoTox™ Complex II + III OXPHOS Activity Assay Kit (ab109905)

  3. BioVision
    Mitochondrial Complex III Activity Assay Kit (K520)

Membrane potential dyes

  1. Perry, 2011, mitochondrial membrane potential probes and proton gradient

  2. Mitra, 2010, analysis of mitochondrial dynamics and functions using imaging approaches


Domain of Applicability

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Evidence for Perturbation by Stressor


Overview for Molecular Initiating Event

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References

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