Iodide is a low charge density anion and is regarded as a chaotrope within the Hofmeister series, so it was expected to decrease protein stability. Initially iodide modulated lysozyme thermal stability in a similar manner to chloride (a small initial dip in lysozyme Tm was observed). With the addition of 0.50 mM NaI the of lysozyme decreased by 0.38 oC. Tm With the addition of a further 0.50 mM NaI (bringing the total concentration to 1 mM) the Tm of lysozyme increased by 0.23 oC. Further addition of NaI caused the of lysozyme to Tm slowly decline, decreasing by 0.33 oC between 1 and 10 mM. Table and give 4.2 figure 4.2 thermodynamic parameters calculated by the NanoAnalyze software and the modified equation for lysozyme unfolding in the presence of NaI (0 10 mM). – NaI (mM) Tm (oC) (kJ/mol-1) (kJ/mol-1 k-1) (kJ/mol-1) ΔH(Tm) ΔS(Tm) ΔΔG(Tm) 0 73.22 463.63 1.34 0.00 0.125 72.97 463.70 1.34 -0.34 0.25 72.97 460.09 1.33 -0.33 0.5 72.84 466.66 1.35 -0.51 1 73.07 466.27 1.35 -0.20 73.07 458.39 1.32 -0.20 2 3 73.04 460.01 1.33 -0.24 4 72.99 461.61 1.33 -0.31 5 72.89 450.65 1.30 -0.43 6 72.89 462.89 1.34 -0.44 10 72.74 454.94 1.32 -0.63 Phosphate is a high charge density anion and considered to be a strong kosmotrope within the Hofmeister series, so it was be expected to increase protein stability. Phosphate
Iodide is a low charge density anion and is regarded as a chaotrope within the Hofmeister series, so it was expected to decrease protein stability. Initially iodide modulated lysozyme thermal stability in a similar manner to chloride (a small initial dip in lysozyme Tm was observed). With the addition of 0.50 mM NaI the Tm of lysozyme decreased by 0.38 oC. With the addition of a further 0.50 mM NaI (bringing the total concentration to 1 mM) the Tm of lysozyme increased by 0.23 oC. Further addition of NaI caused the Tm of lysozyme to slowly decline, decreasing by 0.33 oC between 1 and 10 mM. Table 4.2 and figure 4.2 give thermodynamic parameters calculated by the NanoAnalyze software and the modified equation for lysozyme unfolding in the presence of NaI (0 – 10 mM). NaI (mM) Tm (oC) ΔH(Tm) (kJ/mol-1) ΔS(Tm) (kJ/mol-1 k-1) ΔΔG(Tm) (kJ/mol-1) 0 73.22 463.63 1.34 0.00 0.125 72.97 463.70 1.34 -0.34 0.25 72.97 460.09 1.33 -0.33 0.5 72.84 466.66 1.35 -0.51 1 73.07 466.27 1.35 -0.20 2 73.07 458.39 1.32 -0.20 3 73.04 460.01 1.33 -0.24 4 72.99 461.61 1.33 -0.31 5 72.89 450.65 1.30 -0.43 6 72.89 462.89 1.34 -0.44 10 72.74 454.94 1.32 -0.63 Phosphate is a high charge density anion and considered to be a strong kosmotrope within the Hofmeister series, so it was be expected to increase protein stability. Phosphate