Minimal AOT Concentration of Binary Protein Component in Reverse Micellar Extraction

The minimal AOT concentration of a binary proteinmixture containing cytochrome c and lysozyme was investigated, and was found to be smaller than the sum of the minimal AOT concentration of each protein obtained in single-protein systems, whatever the lysozyme molar fraction in the mixture. The water content, W 0 ( =the water/amphiphile molarratio), of the reverse micellar organic phase under the binary minimal AOT concentration became maximum at a lysozyme molar fraction of 0.5. The apparent interfacial area per single head group of AOT in the binary protein system, estimated from viscosity data, was greater than that of a protein-free system, and became maximum at a lysozyme molar fraction of 0.5. The interfacial tension between the protein mixture aqueous solution and AOT/isooctane solution was lower than that for each single-protein aqueous solution. The binary protein mixture containing cytochrome c and lysozyme thus exhibited higher amphiphilic characteristics. These results indicated that the proteins behaved like amphiphilic molecules, especially when both of the proteins coexisted in the reverse micellar phase.