Theoretical and Experimental Study of the Interaction of Protonophore Uncouplers and Decoupling Agents with Functionally Active Mitochondria

Abstract

The purpose of this work was to quantitatively characterize the effectiveness of oxidative phosphorylation uncouplers and decoupling agents in functionally active mitochondria, taking into account their content in the hydrophobic region of the inner membrane of these organelles. When conducting theoretical studies, it is accepted that uncouplers and decouplers occupy part of the volume of mitochondria to exhibit their activity, which is defined as the effective volume. The following quantities characterizing the action of these reagents are considered: (1) concentrations of reagents that cause double stimulation of mitochondrial respiration in state 4 ( $C_{200}$ ); (2) effective distribution coefficient ( $E_{\mathrm{MW}}$ ) - the ratio of the amount of reagents in the effective volume of mitochondria and the water volume; (3) the relative amount of reagents associated with the effective volume of mitochondria ( $U_M/U_T$ ); (4) specific activity of reagents localized in the effective volume of mitochondria ( $A_M$ ). We have developed methods for determining these values, based on an analysis of the dependence of the rate of mitochondrial respiration on the concentration of uncouplers and decoupling agents at two different concentrations of mitochondrial protein in the incubation medium. During experimental studies, we compared the effects of the classical protonophore uncouplers 2,4-dinitrophenol (DNP) and сarbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), the natural uncouplers lauric and palmitic acids, and the natural decouplers α,ω-tetradecanedioic (TDA) and α,ω-hexadecanedioic (HDA) acids that differ both in the structure of the molecule and in the degree of solubility in lipids. Using the developed methods, we have clarified the dependence of the degree of activity of these uncouplers and decoupling agents on the distribution of their molecules between the effective volume of mitochondria and the water volume.

Keywords: Decoupling; Fatty acids; Mitochondria; Oxidative phosphorylation; Uncoupling.