*3.9. Fluorescence Spectral Measurement*

Intrinsic fluorescence spectral measurements were recorded using a fluorescence spectrophotometer F-4600 (Hitachi, Tokyo, Japan). Tris–HCl (50 mmol/L) was used to prepare the protein solution for fluorescence assay. The samples were measured at an emission wavelength of 350 nm to obtain the maximum excitation wavelength and then scanned at this excitation wavelength to record the emission spectra. The *E*m and *E*x slits were set as 5 nm; scan speed was set as 200 nm/min with a response time of 0.1 s [34,35].
