Influence of Cu(II) on the interaction between sulfite and horseradish peroxidase in vitro

This paper discussed the quantitative influence of Cu(II) on the interaction between horseradish peroxidase (HRP) and sulfite (SO32−), which is a derivate of sulfite dioxide in human bodies, by using fluorescence spectrum and ultraviolet (UV) absorption spectrometry in vitro. The results show that under the conditions of physiological pH and room-temperature, Cu(II) can bind strongly with both the protein part and the ferroporphyrin part in HRP at a low concentration (10−4 mol L−1), and the combination constants are 2.047 × 103 and 7.66 × 102 L mol−1, respectively. Under the same conditions, SO32− at low concentrations (<0.15 mol L−1) has little quenching for the fluorescence of HRP at 330 nm, and the combination constant is 0.108 L mol−1. While the fluorescence intensity at 440 nm enhance gradually with the increased concentration of SO32− (<0.1 mol L−1), and the combination constant is 8.219 L mol−1. These indicate that SO32− at low concentration has little reaction with the enzyme protein part in HRP but obvious reaction with the ferroporphyrin part in HRP. After SO32− at low concentrations is added into the HRP-Cu(II) binary system, the reaction constants between SO32− and the enzyme protein part in HRP increase rapidly. Compared with the absence of Cu(II), the combination constant of SO32− with the enzyme protein part in HRP increases nearly 70 times with a certain Cu(II) concentration (5.0 × 10−4 mol L−1) in the system. However, the presence of Cu(II) in the system has little effect on the reaction constants between SO32− and the ferroporphyrin part in HRP.