Significance of surface potential in interaction of 8-anilino-1-naphthalenesulfonate with mitochondria: fluorescence intensity and zeta-potential.

The 8-anilino-1-naphthalenesulfonate (Ans) fluorescence in nonenergized and energized mitochondria was measured at various concentrations of Ans and KCl. Under the same experimental conditions, the zeta potential was determined from measurements of the electrophoretic mobility of mitochondria. The fluorescence intensity under various conditions was represented quantitatively in terms of the Langmuir adsorption isotherm where the electrostatic interaction acting between Ans and mitochondria was properly taken into account. The values of qN (q) proportionally constant related to quantum yield of Ans: N, the maximum number of the adsorption site) and deltaG (nonelectrical part of the free-energy change due to the binding of Ans to mitochondria) were constant irrespective of difference in energy state and in ionic strength in media. It was concluded that changes in the Ans fluorescence in mitochondria are mainly attributed to changes in the surface potential of mitochondria.