Mechanism of nano-anatase TiO2 on promoting photosynthetic carbon reaction of spinach

Having a photocatalyzed characteristic, our previous research had proved that nano-anatase TiO₂ is closely related to the photosynthesis of spinach. It could not only improve the light absorbance and the transformation from light energy to electron energy and to active chemical energy but also promote carbon dioxide (CO₂) assimilation of spinach. However, the mechanism of carbon reaction promoted by nano-anatase TiO₂ remains largely unclear. By electrophoresis and Western blot methods, the results of the experiments proved that Rubisco from the nano-anatase TiO₂-treated spinach during the extraction procedure of Rubisco was found to consist of Rubisco and a heavier molecular-mass protein (about 1200 kDa) comprising both Rubisco and Rubisco activase. The Rubisco carboxylase activity was 2.67 times that of Rubisco from the control and it could hydrolyze ATP in the same manner as Rubisco activase. The total sulfhydryl groups and available sulfhydryl groups of the Rubisco were 32-SH and 21-SH per mole of enzyme more than those of the Rubisco purified from the control, respectively. The circular dichroism spectra showed that the secondary structure of Rubisco from the nano-anatase TiO₂-treated spinach was very different from Rubisco of the control. It suggested that the mechanism of nano-anatase TiO₂ activating Rubisco of spinach was that the complex of Rubsico and Rubisco activase was induced in spinach, which promoted Rubsico carboxylation and increased the rate of photosynthetic carbon reaction.