Lysozyme, human serum albumin (HSA), and liver alcohol dehydrogenase (LADH) have been studied in reverse micellesby frequency domain fluorescence spectroscopy. The emission of the tryptophanyl residues of the proteins was monitored.Fluorescence and anisotropy decays were measured from 2 to 350 MHz for each protein in reverse micelles and in aqueoussolutions. The wide range of modulation frequencies available allowed direct monitoring of the internal motions of tryptophanresidues, occurring in the subnanosecond time range, together with the whole protein rotational dynamics in the micelles.The results indicate that the rotational correlation times for the internal motions and the overall protein rotation in reversemicelles decrease with increasing water concentration. Lysozymes showed peculiar rotational dynamics which reflect denaturationoccurring as the protein increases its water content in the reverse micelle. This effect was not observed for the other proteins.Dynamic measurements appear useful in understanding structural changes arising from the interactions between proteinsand micellar systems.
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