Cardiolipin binds nonyl acridine orange by aggregating the dye at exposed hydrophobic domains on bilayer surfaces

FEBS Lett. 2001 Oct 26;507(2):187-90. doi: 10.1016/s0014-5793(01)02948-9.


10-N-Nonyl acridine orange (NAO) has been used at low concentrations as a fluorescent indicator for cardiolipin (CL) in membranes and bilayers. The mechanism of its selective fluorescence in the presence of CL, and not any other phospholipids, is not understood. The dye might recognize CL by its high pK (pK(2)>8.5). To investigate that, we established that NAO does not exhibit a pK in a pH range between 2.3 and 10.0. A second explanation is that the dye aggregates at hydrophobic domains on bilayers exposed by the CL. We found that a similar spectral shift occurs in the absence of CL in a concentrated solution of the dye in methanol and in the solid state. A model is proposed in which the nonyl group inserts in the bilayer at the hydrophobic surface generated by the presence of four chains on the phospholipid.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acridine Orange / analogs & derivatives*
  • Acridine Orange / metabolism*
  • Binding Sites
  • Cardiolipins / metabolism*
  • Fluorescent Dyes / metabolism*
  • Hydrophobic and Hydrophilic Interactions
  • Lipid Bilayers / metabolism*
  • Spectrometry, Fluorescence / methods


  • Cardiolipins
  • Fluorescent Dyes
  • Lipid Bilayers
  • N(10)-nonylacridine orange
  • Acridine Orange