DYNAMICS OF ACYLODAN-LABELED BOVINE AND HUMAN SERUM-ALBUMIN SEQUESTERED WITHIN AEROSOL-OT REVERSE MICELLES

We investigate the effects of hydration on acrylodanlabeled bovine and human serum albumin (BSA-Ac and HSA-Ac) in aerosol-OT (AOT) reverse m icelles solubilized in n-heptane. Time-resolved fluorescence intensity decay experiments reveal a dipolar relaxation process surrounding the acrylodan cybotactic region. This process is best described by a two- term rate law wherein the average relaxation increases with increased hydration. However, the actual rate constants describing the relaxatio n process either remain unchanged or actually decrease with increased hydration. The results illustrate that the fractional contribution ass ociated with the individual relaxation pathways causes the observed ch anges in relaxation dynamics. The recovered rotational reorientation d ynamics of the acrylodan residue are also affected by the extent of pr otein hydration. As hydration is increased, the semiangle through whic h the acrylodan residue precesses increases by 10 degrees for both pro tein systems. Interestingly, the recovered semiangles for the native p roteins equal those recovered at lower hydration when the proteins are sequestered within the AOT reverse micelle. These results demonstrate the importance of hydration on protein behavior in environments where water is limited (e.g., biosensor interfaces and sol-gel-derived bioc omposites).