Hydrogen peroxide (H 2 O 2 ) irreversibly inactivates creatine kinase from Pelodiscus sinensis by targeting the active site cysteine.

Creatine kinase (EC 2.7.3.2, CK) plays an important role in cellular energy metabolism and homeostasis by catalysing the transfer of phosphate between ATP and creatine phosphate. In this study, we investigated the effects of H2 O2 on PSCKM (muscle type creatine kinase from Pelodiscus sinensis) by the integrating method between enzyme kinetics and docking simulations. We found that H2 O2 strongly inactivated PSCKM (IC50 =0.25mM) in a first-order kinetic process, and targeted the active site cysteine directly. A conformational study showed that H2 O2 did not induce the tertiary structural changes in PSCKM with no extensive exposure of hydrophobic surfaces. Sequential docking simulations between PSCKM and H2 O2 indicated that H2 O2 interacts with the ADP binding region of the active site, consistent with experimental results that demonstrated H2 O2 -induced inactivation. Our study demonstrates the effect of H2 O2 on PSCKM enzymatic function and unfolding, and provides important insight into the changes undergone by this central metabolic enzyme in ectothermic animals in response to the environment.