Effect of pH on optical and MCD spectra of ShpM66A and ShpM153A. A, the spectral shift of ShpM66A as a function of pH. pH values: 9.0, 8.1, 7.7, 7.3, 6.7, 5.9. B, MCD spectra of ShpM66A at the indicated pH. C, pH titration curve of A600 of ShpM66A. D and E, Optical and MCD spectra of ShpM153A at different pH the indicated pH. The arrows indicate the direction of the shift as pH decreased.