Effects of Ce3+, Cd2+, and Hg2+ on activities and secondary structure of trypsin

The different effects of Ce3+, Cd2+, and Hg2+ on the activities and secondary structure of trypsin were studied. The results showed that trypsin activity was increased substantially by Ce3+ in 0.5–5 µmol/L concentration, but the activity was decreased significantly by Cd2+ or Hg2+ in 0.5–5 µmol/L concentration. The ultraviolet-visible spectrum of trypsin with 4 µmol/L Ce3+ treatment was the same as that of the control, but the 232-nm characteristic peak of trypsin with 4 µmol/L Cd2+ or Hg2+ treatment was blue-shifted and the peak intensity weakened. The circular dichroism (CD) spectrum of trypsin with 4 µmol/L Ce3+ treatment was similar to that of the control. The secondary structure of trypsin did not change with Ce3+ treatment. However, the CD spectrum of trypsin with 4 µmol/L Cd2+ or Hg2+ treatment was different from that of the control and Ce3+ treatment. The secondary structure of trypsin with Cd2+ or Hg2+ treatment changed greatly; for example, the α-helix and β-sheet contents were reduced significantly, the β-turn was enhanced greatly, and the random coil contents increased or decreased.