Fluorescence studies of tryptophan and Human Serum Albumin (HSA) in AOT reverse micelles

摘要

The fluorescence properties of tryptophan derivatives in dioctyl sodium sulfosuccinate (AOT)/iso-octane/buffer reverse micelles were studied using the intrinsic fluorescence of the indole group. The fluorescence decay is more complex for both N-acetyl-1-tryptophan-amide (NATA) and Human Serum Albumin (HSA) in AOT reverse micelles than in aqueous solution. Time-resolved anisotropy and fluorescence quenching studies using carbon tetrachloride suggest one species of NATA lies on the internal micellar interface and another lies embedded in the interfacial region. The fluorescence decay of HSA in AOT reverse micelles has three unchanging exponential components over the ω{sub}0 (the ratio of the concentration of water to AOT) range 9-51, indicating the environment of the tryptophan residue does not change in this range of waterpool size. Fluorescence quenching experiments of HSA in reverse micelles using acrylamide and carbon tetrachloride show that, like NATA, HSA also lies in the interfacial region. There is a minimum in the static component of quenching by CCl{sub}4 of HSA in reverse micelles at ω{sub}0=21. This may be due to conformational stability around this waterpool size, and providing this is not an HSA-specific effect, may correlate with the enhancement of enzyme activity often observed in reverse micelles at a particular waterpool size.