The purpose of this research is to investigate the effects of the variously sulfated chitosans on lysozyme activity and structure. It was shown that the specific enzymatic activity of lysozyme remained almost similar to the native protein after being bound to 6-O-sulfated chitosan （6S-chitosan） and 3,6-O-sulfated chitosan （3,6S-chitosan）, but decreased greatly after being bound to 2-N-6-O-sulfated chitosan （2,6S-chitosan）. Meanwhile, among these sulfated chitosans, 2,6S-chitosan induced the greatest conformational change in lysozyme as indicated by the fluorescence spectra. These findings demonstrated that when sulfated chitosans of different structures bind to lysozyme, lysozyme undergoes conformational change of different magnitudes, which results in corresponding levels of lysozyme activity. Further study on the interaction of sulfated chitosans with lysozyme by surface plasmon resonance （SPR） suggested that their affinities might be determined by their molecular structures.
The interactions between bovine serum albumin(BSA) and gold nanoparticles(AuNPs) ,and the conformational changes of BSA induced by this interaction,were investigated by UV-visible absorption spectroscopy,fluorescence spectroscopy,and Fourier transform infrared in combination with attenuated total reflection spectroscopy(ATR-FTIR) .The critical adsorption density for preventing AuNP aggregation in 0.1 mol/L phosphate buffered saline(pH 7.2) was 23 BSA molecules per gold particle or 3.8×1012 BSA molecules/cm2.BSA bound to the AuNPs with high affinity(binding constant Ks=7.59×108 L/mol) ,and the intrin-sic fluorescence of BSA was quenched by the AuNPs in accordance with the static quenching mechanism.Both fluorescence spectroscopy and ATR-FTIR showed that AuNPs induced conformational changes in BSA,which resulted in it becoming less compact and increased the polarity of the microenvironment around the tryptophan residue Trp-212.
SHI XiuJuanLI DanXIE JingWANG ShawnWU ZhaoQiangCHEN Hong
