Mitochondria are an alternative biocatalyst to microbes and enzymes in bioelectrochemical applications, including biosensors and biofuel cells. However, the bioelectrocatalytic mechanism is not well understood and there are contradictory reports in the literature. The electrochemical communicating species for mitochondria has previously been reported to be ubiquinone, cytochrome c, or cytochrome c oxidase. In this paper, it is determined that the primary electrochemical communicating species in mitochondria is ubiquinone by comparing yeast wild-type and mutants without cytochrome c and cytochrome c oxidase. The electrochemical results compared healthy and unhealthy yeast mitochondria, as established by a Seahorse oxygen consumption assay. Healthy mitochondrial electrochemical response increased by 20 +/- 7% for reduction and 51 +/- 3% for oxidation while unhealthy mitochondrial response increased 3 +/- 50% for reduction and 39 +/- 3% for oxidation when uncoupled with DNP. These responses provide a better understanding of mitochondrial systems in vitro and their relationship to in vivo systems as well as insights into the mechanism of electrochemical response. (C) The Author(s) 2016. Published by ECS. All rights reserved.