Interaction of biological membranes with substituted 1,4-anthraquinones

The interaction of the substituted 1,4-anthraquinones with purple membranes (PM) is studied by the fluorescence and electric light scattering techniques. Substituted 1,4-anthraquinones are shown to quench bacteriorhodopsin tryptophan fluorescence. The quenching efficiency of 1,4-anthraquinone derivatives is smaller than that of 1,4-anthraquinone. It is the smallest at di-substituted 1,4-anthraquinones (R9 = OCOCH3 and R3 = Cl or Br). The type of the halogen atom as substituent does not affect the quenching efficiency of di-substituted 1,4-anthraquinones (R9 = OH or OCOCH3 and R3 = Cl or Br). The quenching efficiency depends on the position of the Cl atom for di-substituted 1.4-anthraquinone derivatives (R9 = OH and R3 = Cl or R9 = OH and R10 = Cl). 9-Hydroxy-1,4-anthraquinones induce decrease in purple membrane charge asymmetry distribution whereas mono-substituted 1,4-anthraquinones containing R9 = OCH3 or R9 = OCOCH3 induce increase in the membrane charge asymmetry. The membrane electric polarizability, related to the structure and dynamics of the electric double layer, decreases in the presence of 1,4-anthraquinone derivatives, the greatest effect being observed for the 9-hydroxy-1,4-anthraquinones. The energy transfer and the quenching of bR tryptophan fluorescence from 9-hydroxy-1,4-anthraquinones correlate with the variation of the surface electric properties of PM in the presence of relatively low concentrations of substituted 1,4-anthraquinones. (C) 2002 Elsevier Science B.V. All rights reserved.