Abstract
The acidity and lipophilicity of the fluorinated arylalkylsulphonamides are determined by the nature of the substituents on their aromatic rings. Herbicidal and anti-inflammatory effects of these compounds appear to increase with their lipophilicity. According to Mitchell's chemiosmotic theory, lipophilic weak-acid uncoupling agents act by transporting protons across the inner mitochondrial membrane and thus destroying the proton-electrochemical potential gradient required for ATP synthesis and ion transport. 1:1:1-Trifluoro- N-[2-methyl-4-(phenylsulphonyl) phenyl]methanesulphonamide (Perfluidone), a pre- and post-emergence herbicide (at 20 μM. concentration), in isolated rat-liver mitochondria caused (1) a 2-fold stimulation of metabolic state-4 respiration, (2) a reduction of respiratory control ratio (RCR) by at least 50%, (3) an enhancement of latent ATPase activity by 40%, (4) a significant passive swelling of mitochondria in 0.15 N NH 4Cl(ΔA 520 = −0.046 ± 0.003), (5) proton intrusion during State-4 respiration (356 ng H + min mg protein; ng H + min mg protein with 5 μM perfluidone), and (6) at least 100% stimulation of oligomycin-inhibited respiration. These profiles are qualitatively comparable with those of the classical lipophilic weak-acid uncoupler, carbonylcyanide-trifluoro-methoxyphenylene hydrazone (FCCP), which acts by promoting the electrogenic transport of H + ions across mitochondrial membrane.
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