Abstract: 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.

Key words: Pepsin, Dimethyl sulfoxide, Tetrahydrofuran, Kinetics, Spectrum