C-phycocyanin incorporated into reverse micelles: a fluorescence study

The solubilization of C-PC into aerosol-OT(AOT, sodium bis(2-ethylhexyl)sulphosuccinate)/water/i-octane reverse micelles has been investigated by fluorescence spectroscopy by following its behaviour as a function of the water-to-surfactant molar ratio, w(0). The maximum wavelength emission decreased steadily with an increase in water content, together with a concomitant increase in steady-state anisotropy. These effects saturated at a w(0) of around 30 and remained practically constant at w(0) > 30. These results are explained in terms of an inclusion into the inner core of the reverse AOT micelles. Strong interactions also took place between amino-acid residues neighbouring bilin chromophores and the AOT sulfonate headgroups, which resulted in the chromophores being located in the structured interfacial micellar water layer. The stabilization rate of the spectral parameters from micelles of protein solutions at pH 5.0 followed pseudo-first-order kinetics and afterwards remained stable for some days. The fluorescence intensity decay of C-PC in reverse micelles is described by a triple exponential function, showing a similar complex pattern to that in an aqueous solution. The fluorescence lifetime values of micelled C-PC indicate that the chromophores are shielded against solvent quenching by the structured interfacial water layer. (C) 2000 Elsevier Science B.V. All rights reserved.