The Mechanism of the Molecular Interaction between Cerium (III) and Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (Rubisco)

The mechanism of the molecular interaction between Ce 3+ , a member of rare earth elements, and Rubisco in vitro is investigated. The carboxylase activity of Rubisco greatly increased under low concentrations of Ce 3+ and decreased under high concentrations of Ce 3+ . The ultraviolet absorption spectra show that the various concentrations of Ce 3+ treatment do not shift the characteristic peaks of Rubisco while the characteristic peak intensity of Rubisco increases with increasing Ce 3+ concentration. The Rubisco–Ce 3+ interactions also do not cause any noticeable change in the λmax of Rubisco fluorescence spectra. However, the fluorescence intensity of Rubisco is found quenched by the addition of Ce 3+ , which strongly suggests that Ce 3+ could directly bind to the Rubisco protein. and the binding sites is estimated to 1.52 per protein. The binding between Ce 3+ and Rubisco is also proved by extended X-ray absorption fine-structure essay; Ce 3+ coordinated with eight oxygen atoms of Rubisco in first shells and six oxygen atoms in second shells. The results implied that Ce 3+ might improve the microenvironment of Rubisco and, in turn, affected the carboxylase capacity of Rubisco greatly.