二甲基亚砜和四氢呋喃对胃蛋白酶催化动力学和分子光谱的影响

为了研究二甲基亚砜(DMSO)和四氢呋喃(THF)对胃蛋白酶(Pepsin, PP)催化活性的影响及其作用本质, 测定了在这两种有机溶剂的作用下胃蛋白酶的催化活性、 动力学参数、 紫外吸收光谱、 紫外差示光谱和荧光发射光谱的变化. 结果表明, 体积分数为9%的DMSO使PP活性提高83.4%; 而体积分数为1%的THF只能使PP活性提高3.59%. 在盐酸溶液中, PP的动力学参数K_m=2.22 mg/mL, v_max=1.1×10⁶ U/mg Pro; 在9%DMSO中, 其K_m=1.50 mg/mL, v_max=0.5×10⁶ U/mg Pro; 在1%THF中的K_m=1.91 mg/mL, v_max=0.51×10⁶ U/mg Pro. 9%DMSO强烈抑制PP分子肽键的紫外吸收, 而对芳香族氨基酸无影响; 1%THF则对PP的紫外吸收光谱影响不大. 9%DMSO和1%THF都使PP的紫外差示光谱出现明显的负吸收峰和正吸收峰. 9%DMSO使酶分子的荧光发射峰向短波方向移动1 nm; 而1%THF则对其无影响. 实验结果表明, 在9%DMSO和1%THF中, PP分子的立体构象发生了变化, 使酶分子的K_m下降, 酶分子对底物的亲和力有所升高, 从而导致酶分子的催化活性有不同程度的提高.

Effects of Dimethyl Sulfoxide and Tetrahydrofuran on the Catalytic Kinetics and Molecular Spectra of Pepsin

In order to approach the effects and action mechanism of dimethyl sulfoxide(DMSO) and tetrahydrofuran(THF) on pepsin,the catalytic activity,kinetics parameters,ultraviolet absorption spectra,ultraviolet differential spectra,and fluorescence emission spectra of pepsin were investigated.It was indicated that pepsin activity was enhanced by 83.4% as the enzyme was treated with 9%DMSO.But when pepsin was treated with 1%THF the enzyme activity was enhanced only by 3.59%.In hydrochloric acid solution the kinetics parameter of the enzyme, K m=2.22 mg/mL,v max=1.1×106 U/mg Pro.In 9%DMSO, K m=1.50 mg/mL,v max=0.5×106 U/mg Pro.In 1%THF,K m=1.91 mg/mL and v max=0.51×106 U/mg Pro.In 9%DMSO the ultraviolet absorption of pepsin peptide bonds was strongly inhibited.But the ultraviolet absorption of aromatic amino acids of pepsin was not inhibited.The ultraviolet absorption of pepsin molecules was not influenced obviously in 1%THF.Both in 9%DMSO and in 1%THF the ultraviolet differential spectra of pepsin showed obvious positive and negative peaks.The fluorescence emission peak of pepsin enzyme moved to short wavelength direction by 1 nm in 9%DMSO.But in 1% THF the fluorescence emission spectrum did not change obviously.It was concluded from these results that the conformation of pepsin molecules changed obviously in both 9%DMSO and 1%THF.This led the K m value of the enzyme descended and the affinity of the enzyme to substrates enhanced.So the catalysis activities of the enzyme were increased in some extent in these solutions.