, Volume 121, Issue 3, pp 249-257
Date: 30 Oct 2007

Effect of Mg2+ on the Structure and Function of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase

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Abstract

Mg2+ in various concentrations was added to purified Rubisco in vitro to gain insight into the mechanism of molecular interactions between Mg2+ and Rubisco. The enzyme activity assays showed that the reaction between Rubisco and Mg2+ was two order, which means that the enhancement of Rubisco activity was accelerated by low concentration of Mg2+ and slowed by high concentration of Mg2+. The kinetics constant (K m) and V max was 1.91 μM and 1.13 μmol CO2 mg−1 protein∙min−1, respectively, at a low concentration of Mg2+, and 3.45 μM and 0.32 μmol CO2∙mg−1 protein∙min−1, respectively, at a high concentration of Mg2+. By UV absorption and fluorescence spectroscopy assays, the Mg2+ was determined to be directly bound to Rubisco; the binding site of Mg2+ to Rubisco was 0.275, the binding constants (K A) of the binding site were 6.33 × 104 and 5.5 × 104 l·mol−1. Based on the analysis of the circular dichroism (CD) spectra, it was concluded that the binding of Mg2+ did not alter the secondary structure of Rubisco, suggesting that the observed enhancement of Rubisco carboxylase activity was caused by a subtle structural change in the active site through the formation of the complex with Mg2+.