Effect of Riboflavin Metabolites on Mitochondrial Electrochemistry

Abstract

Mitochondrial deficiency is the cause of many diseases and the determination of changes in metabolic rates usually requires lysing of the mitochondria and isolating individual mitochondrial proteins. Alternatively, mitochondria can be immobilized on electrode surfaces to utilize electroanalytical evaluation of metabolic rates of intact mitochondria. However, the redox mechanisms are still poorly understood. In this paper, the riboflavin cycle of mitochondria is studied electrochemically and its impact on mitochondrial voltammetry is discussed. The inhibition mechanism of mitochondria by three different inhibitors (rotenone, carboxin, and permethrin) is discussed and it is found that the inhibition behavior observed electrochemically is due to not only ubiquinone, which is the electrochemical communicating species of mitochondrial electrochemistry. It is also shown that riboflavin derivatives interact with ubiquinone leading to a change in the intensity of ubiquinone voltammetry peaks. This interaction is affected by altering the choice of solvent used during the electrode preparation process. Finally, it is concluded that the observed voltammetry of mitochondrial inhibition is due to a change in riboflavin metabolism within the intact mitochondria immobilized on carbon electrodes. Mitochondria are the primary source of respiration and ATP synthesis for all eukaryotic cells. The mitochondrial electron transport chain (ETC), which is responsible for mitochondrial respiration, contains four proteins (three for fungal mitochondria) and ATP synthase as well as multiple electrochemically active species such as ubiquinone and cytochrome c. Mitochondria contain the proteins of the Krebs cycle 1-3 that are capable of metabolizing sugar metabolites, fatty acids 4 and amino acids 5 and have therefore been considered as attractive catalysts for bioelectrocatalysis applications such as biofuel cells, due to their high volumetric catalytic activity. The metabolism integrity and complexity also allows mitochondria to be responsive to many different toxins, such as inhibitors (rotenone, carboxin, etc.), uncouplers (dinitrophenol, dicumarol) and other toxins (cyanide, azide, CO), with different electrochemical responses toward different toxins. 6,7 Since mitochondrial ETC deficiency has been recognized as the reason for many diseases and disorders, like early age hypertonia, Kearns-Sayre syndrome, Alzheimer's and Leber's hereditary optic neuropathy, 8 an electrochemical biosensor incorporating mitochondria could possibly be an alternative biosensor technology to the current mitochondria deficient study that is based on mouse models.The electrochemistry of mitochondria has been extensively studied. In terms of practical application, mitochondrial fuel cells with advantageous fuel adaptation, power output and complete biofuel oxidation as well as mitochondrial biosensors with universality have been reported. 6,7,[9][10][11][12][13][14] Mitochondria contain many different electrochemically active species, like flavin adenine dinucl...

Ubiquinone electrochemistry in analysis and sensing

“…A further study found that mitochondrial electrochemistry could be altered by the addition of effectors. [ 61 ] Thus riboflavin derivatives were found to interact with UQ in the mitochondria and to alter the observed electrochemistry. Such electrochemical behavior of these sub‐cellular assemblies provides the basis for their use in new biosensing or bioanalytical strategies.…”

Assessment of the Maximal Activity of Complex IV in the Inner Mitochondrial Membrane by Tandem Electrochemistry and Respirometry

“…To achieve this, the electrochemical method should ensure that the overall rate limiting step, including mass transport of the mediator, is a function of the ETC enzyme(s) of interest. In the studies on the coenzyme Q pool, for example, the limitations of mass transport were circumvented by immobilizing mitochondria on the electrode, , although this could affect the integrity of the OMM or the signaling pathways . The proximal and distal sides of an immobilized mitochondrion may also exhibit different electrode kinetics.…”