【摘要】 在不同的pH值体系中,利用酶活测量、圆二色谱、荧光谱和电子吸收谱研究了十二烷基磺酸钠(SDS)对大豆过氧化物酶(SBP)活性与构象的影响情况.在pH2.6和4.2的体系中,少量的SDS分子可通过静电作用与SBP结合,进而与SBP分子中的His169残基结合,降低其与铁卟啉的配位能力,使其Soret吸收带蓝移,二级结构发生轻微的变动,活性永久丧失.在pH5.2体系中,SDS和SBP分子都带负电,由于静电排斥作用,SDS无法进入SBP的分子内部,失去与SBP分子中His169残基结合的能力,对SBP分子的二级结构没有影响,仅对SBP分子的三级结构有所影响.当SDS的浓度大于临界胶束浓度时,由于胶束与SBP的静电排斥作用增强,限制了铁卟啉中乙烯基的运动,乙烯基与卟啉环的共轭程度增大,Soret吸收带红移.由于SBP活性可完全恢复,此变化是可逆的.更多还原

【Abstract】 The effect of sodium dodecyl sulfate (SDS) on the activity and conformation of soybean peroxidase (SBP) was studied by the measurement of activity, far-UV circular dichroism spectra, electronic absorption spectra, and fluorescence spectra at different pH values and 30 ℃ . In the pH 2.6 and 4.2 systems, the interaction of SDS at a submicellar concentration with SBP and then with His169 of SBP due to the electrostatic attraction weakens the binding between imidazole of His169 and Fe(Ⅲ) of heme. As a result of this change, the influence of Fe(Ⅲ) of heme on porphrin ring is increased leading to the blue shift of Soret band. In the meantime, the secondary structure of SBP changes slightly and the activity is lost irreversibly. After the activity of SBP is lost, the α-helix content of SBP is decreased but that of β-strand increased gradually along with the increment of the SDS concentration. In pH 5.2 systems, SDS can not get into the SBP molecule to bind to the His169 since it has the same kind of charge with SBP. When the SDS concentration is lower than its cmc, it has no obvious effect on the secondary structure of SBP, but only has little effect on the tertiary structure. When the SDS concentration is increased above its cmc, the electrostatic repulsive force between the micelles of SDS and SBP is increased evidently so as to restrict the movements of the vinyl substituents in heme of SBP molecules. Therefore the conjugation between the vinyl substituents and the porphrin ring is enforced, which leads to the red shift of Soret band of SBP and change of the tertiary structure. This change is reversible since the SBP activity is recoverable. In conclusion, the precondition of SBP denaturalization is the electrostatic interaction between SDS and SBP, and His169 binding to the heme is the key element of SBP activity.更多还原