The effect of compressed CO2 on the microenvironment of the two proteins (cytochrome c and RNase A) in sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles was investigated using high-pressure steady-state fluorescence and time-resolved fluorescence. It is found that RNase A can shift from the water core to the interface of the reverse micellar cores as CO2 is dissolved, while cytochrome c maintains at the interface of the micellar core. As the pressure reaches to a high enough value, the proteins can be precipitated from the reverse micelle, which has been detected by high-pressure UV-vis technique. The results show that cytochrome c was easier to be precipitated from the reverse micellar solution by CO2 than RNase A. The possible reasons for these behaviors were discussed based on the changes of the microenvironment of the two proteins, which could be tuned by the dissolution of compressed CO2. (C) 2005 Elsevier B.V. All rights reserved.