Native and chemically modified cytochrome c were incorporated in AOT reverse micelles. The native protein is strongly basic whereas the chemically modified protein has been rendered highly acidic. The localisation of the two proteins was determined by reaction kinetics with hydrated electrons. From a kinetic model of the quenching of hydrated electrons with the proteins, the localisation can be deduced. The positively charged native protein was found to be situated at the interface, whereas the negatively charged modified protein was confined inside the water pools without any affinity for the interface. The electrostatic interactions between the native cytochrome c and the surfactant polar head groups are strong enough to have an impact on the physical behaviour of the microemulsion: changes of the phase diagrams and percolation threshold were observed.