Thursday, 5 July 2018

Mitochondrial Supercomplexes Do Not Enhance Catalysis by Quinone Channeling

Fedor JG and Hirst J

  • Components of the electron transport chain have been observed to form respiratory units, called the "respirasome" consisting of 1 CI, 2 CIII and 1 CIV. It has been proposed that the respirasome serves to stabilize CI and mitigate the production of ROS.
  • More controversially, the respirasome has been suggested to confer a kinetic advantage on respiration by trapping/channeling quinone to enhance its transfer between the enzymes in the supercomplex, creating an independent, local quinone pool that does not exchange with the quinone pool outside.
  • The authors test the quinone channeling hypothesis by introducing an external enzyme which competes for quinone. If the substrate is truly channeled, flux through the competing pathway is negligible.
  • The authors introduce the alternative oxidase (AOX) protein. The authors find that AOX competes effectively with the CIII/CIV pathway. Therefore, quinone is not channeled or sequestered by the respiratory-chain supercomplexes.

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