Studies of energy-linked reactions. Inhibition of oxidative phosphorylation by DL-8-methyldihydrolipoate

Abstract

1. DL-8-Methyldihydrolipoate was shown to be a potent inhibitor of mitochondrial oxidative phosphorylation and ATP-driven energy-linked reactions. 2. ADP-stimulated respiration utilizing pyruvate + malate and succinate in both ox heart and rat liver mitochondria is inhibited; oxidative phosphorylation using pyruvate + malate, succinate and ascorbate + NNN'N'-tetramethyl-p-phenylenediamine as substrates is also inhibited; uncoupler-stimulated respiration is unaffected regardless of the substrate used. 3. Mitochondrial oligomycin-sensitive adenosine triphosphatase is inhibited in both the membrane-bound form and the purified detergent-dispersed preparation. 4. ATP-driven transhydrogenase and the ATP-driven energy-linked reduction of NAD+ by succinate in ox heart submitochondrial particles are inhibited, whereas the respiratory-chain-driven transhydrogenase is unaffected. 5. DL-8-Methyl-lipoate has no immediate effect on the above reactions, demonstrating the requirement for the reduced form for inhibition. 6. The inhibitory properties of DL-8-methyldihydrolipoate are analogous to those of oligomycin and provide further evidence of a role for lipoic acid in oxidative phosphorylation.

Studies on energy‐linked reactions: Inhibition of oxidative phosphorylation and energy‐linked reactions by dibutyltin dichloride

“…The sources of all the chemicals used in this study have been described previously [ 1,3] . Dibutyltin dichloride was further purified by fractional distillation as described previously [l] .…”

“…Ox heart mitochondria (BHM) and submitochondrial particles (BHSMP) were prepared as described by Griffiths et al [3] . Mitochondrial respiration, ATPdriven transhydrogenase, ATP-driven reduction of NAD' by succinate, oxidative phosphorylation and ATPase activity were measured as described previously [3] .…”

“…Mitochondrial respiration, ATPdriven transhydrogenase, ATP-driven reduction of NAD' by succinate, oxidative phosphorylation and ATPase activity were measured as described previously [3] . Protein and Pi determination were as described by Griffiths et al [3].…”

“…(a) The reaction medium contained 2.25 mg BHM to which the following additions were made: PM, 10 wmol pyruvate + 1 Fmol malate; ADP, 900 nmol; FCCP, 10 nmol. In addition, 5 r.11 ethanol was added at (I), control; 6.3 nmol of DBCT at (2); 3.3,6.6 and 13.2 nmol DBT added at (3), (4), (5). (b) The following additions were made to the reaction medium which contained 1.6 mg BHM; Succ, 10 pmol succinate; PM, 10 pmol pyruvate + 1 nmol malate; ADP, 600 nmol; FCCP, 10 nmol.…”

“…Inhibition of mitochondrial respiration by DBT. Mitochondrial respiration was recorded as described by Griffiths et al [3]. Inhibitors were added as indicated in maximum vol.…”