光谱法研究CTAB对木瓜酶酶活和构象的影响

Spectroscopic Study on Effect of CTAB on Enzyme Activity and Conformation of Papain

采用荧光光谱、圆二色谱（CD）和紫外光谱研究了十六烷基三甲基溴化铵（CTAB）在NaHPO_4-NaH_2PO_4缓冲溶液中对木瓜酶构象变化及其酶活的影响,并探讨了CTAB与木瓜酶的作用机理。荧光光谱表明.在CTAB存在下,木瓜酶的荧光强度增强.荧光峰发生红移,CTAB使木瓜酶分子链趋于伸展,酪氨酸等发色基团更多地暴露在水中。CD谱表明.当CTAB浓度（C_（CTAB））为0.5 mmol/L时,木瓜酶的α-螺旋构象和β-折叠构象含量比纯木瓜酶（Papain）体系分别增加了1.3%和0.1%,回转构象和无定型构象含量则分别减少了0.3%和1.2%。酶活测定结果表明,CTAB对木瓜酶的酶活有较大影响。当C_（CTAB）由0增加到1.5mmol/L时,木瓜酶酶活由11.2×10~5U/g增大到16.3×10~5U/g,当C_（CTAB）由1.5mmol/L增加到3.5mmol/L,木瓜酶的酶活又由峰值（16.3×10~5U/g）降到11.7×10~5U/g,CTAB使木瓜酶酶活增强与木瓜酶的构象有序度提高有关。

The effects of cetyl trimethyl ammonium bromide（CTAB） on conformation and enzyme activity of papain in NaHPO-4-NaH_2PO_4 buffer were investigated by fluorescence spectrum, circular dichroism（CD） spectroscopy and UV spectrum,and the action mechanism of CTAB with papain was discussed.In the presence of CTAB,the fluorescence spectrum showed the fluorescence intensity of papain enhanced,while the fluorescence peak occurred red-shift,and the molecular chain of papain was tended to spread by CTAB,and more tyrosine residues（chromophore groups） emerged in water.CD spectrum indicated that the concentrations ofα-Helix andβ-sheet of papain respectively increased 1.3%and 0.1%under concentration CATB of 0.5mmol/L than pure papain system,and concentrations of turn and unorder decreased 0.3%and 1.2%than that of pure papain system, respectively.The enzyme activity results showed that CTAB had the large effect on enzyme activity of papain,when the enzyme activity of papain increased from 11.2×0~5U/g to 16.3×10~5U/g,the concentrations of CTAB increased from 0 to 1.5mmol/L,but when the enzyme activity of papain decreased from 16.3×10~5U/g to 11.7×10~5U/g,the concentrations of CTAB varied from 1.5mmol/L to 3.5mmol/L.CTAB can enhance enzyme activity of papain,that is relate with increasing of degree of order of papain conformation.