UV-vis spectra of CYP101, thiolate-ligated CYP101 and selenolate-ligated CYP101: CYP101 (417, 535, 589 nm), PhSH-CYP101 (383 nm, 465 nm, 562 nm), PhSeH-CYP101 (384, 472, 570 nm). PhSH-CYP101 and PhSeH-CYP101 were prepared by adding, respectively, PhSH or PhSeH (~4 equivalents) in ethanol to a 1 mL solution of CYP101 (~5 μM) in 100 mM phosphate (pH 7.4) at 20 °C.