Denaturation curves of the PAD4 N153 and D155 mutant enzymes in the presence of calcium ions.

<p>PAD4 mutants in the presence of 10 mM Ca²⁺ were treated with various concentrations of urea in 30 mM Tris-HCl buffer (pH 7.4) at 25°C for 16 h and monitored using intrinsic protein fluorescence. Panels <b>A</b> (N153A), <b>C</b> (N153Q), <b>E</b> (D155A), and <b>G</b> (D155E) correspond to the experimental data of average emission wavelength, and panels <b>B</b> (N153A), <b>D</b> (N153Q), <b>F</b> (D155A), and <b>H</b> (D155E) correspond to the integrated emission fluorescence by intrinsic protein fluorescence. All data were fitted by either a two-state or three-state model. The fitting results and residues are shown as a solid line with error bars.