Evaluation and analysis of the toxicity of mercury (Hg) to allophycocyanin from Spirulina platensis in vitro.

As a global environmental pollution problem, heavy metal pollution has brought great harm to human beings. In this work, we studied the toxicity of Hg on allophycocyanin (APC) at the molecular level. Firstly, APC was extracted and purified from Spirulina platensis mud and its purity (A/A) reached 3.75. In addition, the fluorescence intensity of APC decreased with increasing Hg concentration from 0 to 5 × 10 mol L. The theoretical calculation and experimental results showed that the fluorescence quenching of APC by Hg was static and had a good linear relationship. Moreover, the UV-Vis spectra of APC showed a significant decrease at 200 nm and 650 nm with the increase of Hg concentration from 0 to 5×10 mol L, and a red-shift at 200 nm, which indicated that Hg not only affected the structure of APC but also affected the light absorption and photosynthetic function of APC. Furthermore, the results of molecular simulation demonstrate that Hg combinations with the Met77, Cys81 in the α chain and the Arg77, Cys81 in the β chain, which interact between the peptide chain and the chromophore, and Hg forms a Hg-S bond with -SH. This study provides new insights into the structure and how Hg effect the optical properties of APC.