6-KETOCHOLESTANOL IS A RECOUPLER FOR MITOCHONDRIA, CHROMATOPHORES ANDCYTOCHROME-OXIDASE PROTEOLIPOSOMES

The effect of 6-ketocholestanol (kCh) on various natural and reconstit uted membrane systems has been studied. 6-ketocholestanol (5 alpha-Cho lestan-3 beta-ol-6-one), a compound increasing the membrane dipole pot ential, completely prevents or reverses the uncoupling action of low c oncentrations of the most potent artificial protonophore SF6847. This effect can be shown in the rat liver and heart muscle mitochondria, in the intact lymphocytes, in the Rhodobacter sphaeroides chromatophores , and in proteoliposomes with the heart muscle or Rh. sphaeroides cyto chrome oxidase. The recoupling effect of kCh disappears within a few m inutes after the kCh addition and cannot be observed at all at high SF 6847 concentrations. Almost complete recoupling is also shown with FCC P, CCCP, CCP and platanetin. With 2,4-dinitrophenol, fatty acids and g ramicidin, kCh is ineffective. With TTFB, PCP, dicoumarol, and zearale none, low kCh concentrations are ineffective, whereas its high concent rations recouple but partially. The kCh recoupling is more pronounced in mitochondria, lymphocytes and proteoliposomes than in chromatophore s. On the other hand, mitochondria, lymphocytes and proteoliposomes ar e much more sensitive to SF6847 than chromatophores. A measurable lowe ring of the electric resistance of a planar bilayer phospholipid membr ane (BLM) are shown to occur at SF6847 concentrations which are even h igher than in chromatophores. In BLMs, kCh not only fails to reverse t he effect of SF6847, but even enhances the conductivity increase cause d by this uncoupler. It is assumed that action of low concentrations o f the SF6847-like uncouplers on coupling membranes involves cytochrome oxidase and perhaps some other membrane protein(s) as well. This invo lvement is inhibited by the asymmetric increase in the membrane dipole potential, caused by incorporation of kCh to the outer leaflet of the membrane.