CYTOCHROME-C IN REVERSE MICELLES - SMALL-ANGLE X-RAY-SCATTERING MEASUREMENTS, PERCOLATION PROCESS, AND CRITICAL-BEHAVIOR - AN INTERPRETATION WITH AN ASSOCIATION MODEL

It has been shown that solubilization of cytochrome-e in water in oil reverse micellar systems induces a change in the small angle x-ray sca ttering (SAXS) spectrum which suggests an increase in the attractive p art of the intermicellar potential. In addition, from conductivity mea surements a percolation threshold appears for a micellar concentration which is smaller than that observed without protein. Finally, for the liquid-liquid phase transition, a decrease in the critical temperatur e and concentration is observed. To explain these results, we introduc e a pairing sticky hard sphere model. In this approach, the empty mice lles are described by the sticky hard sphere model as is usually done. The presence of cytochrome-e is represented by an additional attracti ve potential characterized by an association parameter that leads to t he pair formation of micelles. The association parameter was determine d by fitting the experimental structure factors and from this paramete r the decrease in the percolation threshold has been estimated. The ch ange in the critical parameters induced by cytochrome-e can be interpr eted in terms of formation of micelle-pairs and not by a van der Waals -type theory. These results are also supported by dynamic light scatte ring experiments. (C) 1997 American Institute of Physics.