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 lambda max 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.