Key Event Title
|Level of Biological Organization|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|Mitochondrial complex inhibition leading to liver injury||MolecularInitiatingEvent|
|Complex III inhibition leading to growth inhibition (1)||MolecularInitiatingEvent|
|Complex III inhibition leading to growth inhibition (2)||MolecularInitiatingEvent|
Key Event Description
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:
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
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)
Complex inhibition assays
MitoCheck® Complex II/III Activity Assay Kit (Item No. 700950)
MitoTox™ Complex II + III OXPHOS Activity Assay Kit (ab109905)
Mitochondrial Complex III Activity Assay Kit (K520)
Membrane potential dyes
Perry, 2011, mitochondrial membrane potential probes and proton gradient
Mitra, 2010, analysis of mitochondrial dynamics and functions using imaging approaches
Domain of Applicability
Evidence for Perturbation by Stressor
Overview for Molecular Initiating Event