Impact Assessment of heavy metal cations to the characteristics of photosynthetic phycocyanin.

This work has assessed the impact of typical heavy metal cations on C-phycocyanin in vitro and in silico. At low concentrations (<2×10-6 mol/L), the influence of Pb2+ is the highest on the light absorption of C-phycocyanin trimer. At higher concentrations, however, a new order of influence on the light absorption has been observed with Cd2+ < Cu2+ < Pb2+ < Zn2+. The fluorescence polarization has changed from the order of Cd2+ < Pb2+≈Cu2+ < Zn2+ to Cd2+ < Cu2+ < Pb2+ < Zn2+, when the metal concentrations reaches 2×10-6 mol/L. The mechanisms for these findings have been studied using FTIR, hydrophobic probe, isothermal titration calorimetry and molecular docking for the analysis of structure disorder of C-phycocyanin. It has been suggested that the secondary structure of C-phycocyanin affects more to the light absorbance while the fluorescence characteristics relies more on the tertiary structure. The interaction between Pb2+ and C-phycocyanin is both enthalpically and entropically favoured, whereas the interactions for Cd2+, Cu2+ and Zn2+ are entropically driven. The ion-molecular docking suggests that the structure disorder of C-phycocyanin relies on the molecular interactions with metal ions. The in silico study also showed that the binding cites of Zn2+ are closer to chromophores.

In vitro assessment of the toxicity of small silver nanoparticles and silver ions to the red blood cells.

This work reports the toxicity of small silver nanoparticles (nanoAg, 20 nm) and silver ions (Ag+) to the red blood cells with the silver concentration level of 10-6 g/mL. Results show that red blood cells (RBCs) start hemolysis when treated by nanoAg of 1.5 × 10-5 g/mL or Ag+ of 2.9 × 10-7 g/mL. A low ATPase activity of 30% has been observed after RBCs being treated with Ag+ of 2.6 × 10-7 g/mL, while the nanoAg does not obviously affect the ATPase activity. In molecular level, Ag+ is more toxic to the amino acid residues than nanoAg according to the change of fluorescence characteristics of hemoglobin (Hb). However, the nanoAg has been found to be more toxic than Ag+ to the secondary structure of Hb in terms of the loss of α-helix content.

In vitro assessment of the toxicity of lead (Pb2+) to phycocyanin.

This work reports the influence of lead (Pb2+) on fluorescence characteristics and protein structure of phycocyanin molecules experimentally in vitro. The fluorescence intensity decreases with the increasing concentration of Pb2+ from 0 to 5 × 10-5 mol L-1, showing the fluorescence quenching of phycocyanin by Pb2+. The quenching process is suggested to be static regarding the calculation results and the experimental results of time-resolved fluorescence decay profiles. The synchronous fluorescence spectra show that the effect of Pb2+ on the Tyr residues of phycocyanin is more significant than the Trp residues. The forming of aggregation by the interaction of Pb2+ with phycocyanin molecules is suggested from the results of resonance light scattering spectra. The UV-Vis spectra of the protein skeleton of phycocyanin have a red-shift of about 10 nm with increasing the Pb2+ concentration from 0 to 5 × 10-5 mol L-1, indicating a change in the protein skeleton and its secondary structure. With the increasing Pb2+ concentration, the two negative peaks (209 nm and 218 nm) on circular dichroism spectra become smaller, showing a decrease of the α-helix structure. These results may give people a deeper understanding of that how the heavy metal (Pb2+) can affect the chemo-physical properties of phycocyanin.

In vitro assessment of phthalate acid esters-trypsin complex formation.

In this work, interactions of three phthalate acid esters (PAEs), including dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), with trypsin have been studied in vitro, under simulated physiological conditions using multi-spectroscopic techniques and molecular modeling. The results show that these PAEs can bind to the trypsin, forming trypsin-PAEs complexes, mainly via hydrophobic interactions, with the affinity order of DMP > DEP > DBP. Binding to the PAEs is found to result in molecular deformation of trypsin. The modeling results suggest that only DBP can bind with the amino acid residues of the catalytic triad and S1 binding pocket of trypsin, leading to potential competitive enzyme inhibition.