Inhibition of Bovine Heart Mitochondrial NADH — Ubiquinone Reductase by Tinopal AN, A Cationic Benzoxazole
The effect of Tinopal AN (1,1-bis(3, N-5 dimethylbenzoxazol-2-yl)-methine p-toluene sulfonate) on the respiration of bovine heart mitochondria was investigated. This compound was found to inhibit electron transport in a concentration dependent manner at site 1, with half maximal inhibition at about 90 uM reagent. Tests with either submitochondrial particles (SMP) or isolated complex I indicate that Tinopal AN specifically inhibits electron flow between NADH and coenzyme Q, and not between NADH and artificial electron acceptors, except menadione. Concentrations of Tinopal AN too low to cause significant inhibition of SMP NADH oxidase activity changed the sigmoid-shaped rotenone inhibition curve to a hyperbolic function, indicating that at low concentrations Tinopal AN may bind at the high affinity lower inhibitory rotenone site within complex I. Kinetics experiments indicate mixed inhibition with respect to coenzyme Q, with a unusual concentration dependent pattern, which may suggest multiple binding sites of differing affinities. This appears to be supported by cross-linking studies which indicate concentration dependent conformational changes do occur within complex I in the presence of Tinopal AN.
KeywordsNADH Dehydrogenase Aerobic Respiration Bovine Heart Paracoccus Denitrificans Submitochondrial Particle
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