【摘要】 采用多种光谱学方法研究了NaCl对橙皮素抑制多酚氧化酶（PPO）活性、与PPO相互作用以及对PPO构象的影响。结果表明，NaCl的浓度变化对PPO的催化速率及酶活性有较大影响，当NaCl浓度<1%时，PPO的催化速率和酶活性急剧下降，当NaCl浓度>1%时，PPO的催化速率和酶活性下降很小。NaCl的存在增强了橙皮素对PPO活性和催化速率的抑制能力以及对PPO内源荧光的猝灭作用和结合亲和力，但没有改变橙皮素对PPO的荧光猝灭类型和主要作用力（仍为静态猝灭机制和疏水相互作用），NaCl浓度的增大（0%～0.5%）对橙皮素与PPO的结合亲和力无显著影响。NaCl的存在导致PPO的α-螺旋含量降低，β-折叠含量增高，PPO的结构部分伸展。在NaCl与PPO反应体系中增加橙皮素的浓度，PPO的α-螺旋含量增加，β-折叠含量降低，酶的结构趋向紧缩，而在PPO-橙皮素体系中逐渐增加NaCl的浓度，α-螺旋含量又逐渐降低，β-折叠含量逐渐增加，NaCl的存在抑制了橙皮素引起的PPO结构紧缩。分子动力学模拟显示0.5%NaCl的存在降低了PPO骨架的稳定性，而橙皮素的加入与PPO形成了构象稳定的复合物，从而减弱了NaCl对PPO结构稳定性的影响。本研究以期为橙皮素在抑制食品褐变的条件优化上提供一定的实验依据。更多还原

【Abstract】 The effects of NaCl on the inhibition of polyphenol oxidase(PPO) activity by hesperetin, the binding property with PPO and the conformation change of PPO were investigated by various spectroscopic methods. The results showed that the concentrational changes of NaCl had a great effect on the catalytic rate and enzyme activity of PPO. When the NaCl concentration was less than 1%, the catalytic rate and enzyme activity of PPO decreased sharply, but they only showed slight decrease as the concentration of NaCl was greater than 1%. The addition of NaCl enhanced the inhibitory ability of hesperetin on PPO activity and catalytic rate, and increased the fluorescence quenching effect on PPO and their binding affinity, but did not change their fluorescence quenching type and main binding force(still was static quenching mechanism and hydrophobic interaction). The increase of NaCl concentration(0%—0.5%) had no significant effect on the binding affinity of hesperidin and PPO. The presence of NaCl led to the reduction in α-helix content of PPO and the increase of β-sheet content, the structure of PPO was partially extended. The concentration of hesperetin was increased in the reaction system of NaCl and PPO, the contents of α-helix and β-sheet of PPO increased and decreased, respectively, the structure of the enzyme tended to tighten. However, in the PPO-hesperetin systems,increased NaCl concentration resulted in the reduction in α-helix content and increase in β-sheet content, indicating that the presence of NaCl inhibited the structural contraction of PPO induced by hesperetin. Molecular dynamics simulations showed that 0.5% NaCl reduced the stability of the PPO skeleton, while the addition of hesperetin formed structurally stable complex with PPO,thus attenuated the effect of NaCl on the stability of PPO structure. This study is expected to provide some experimental basis for optimizing the conditions of hesperetin inhibiting food browning.更多还原