A, changes in enzyme activity over time at 37 °C and relative to wild type UROIIIS at 4 °C. Black circles, wild type UROIIIS; blue diamonds, C73R-UROIIIS; green squares, UROIIIS-Myc. The inset expands the information regarding C73R-UROIIIS. B, decay over time of the CD ellipticity at 222 nm (sensitive to the α-helical content of the protein) for WT and seven different Cys-73 mutants of UROIIIS. C, far-UV region of the CD spectra for wild type (black line) or C73R (blue line) UROIIIS. D, tryptophan emission fluorescence spectra for wild type (black line) or C73R (blue line) UROIIIS. The position of the maximum in each spectrum is highlighted by the vertical lines. The peaks labeled with an asterisk correspond to the Raman spectrum of water. a.u., arbitrary units; mdeg, millidegrees; n.i., normalized intensity.