Extended Data Figure 2. Absolute TR³ spectra of the sMMO reaction with O₂.

Top, reaction using ¹⁶O₂-containing buffer (blue), ¹⁸O₂-containing buffer (red) or buffer background in the absence of MMOH/MMOB (black). Middle, ¹⁶O₂ – ¹⁸O₂ difference spectra of the MMOH^red/MMOB reaction with O₂ at pH 7.0, 4 °C and Δt ≈ 3.0 s. Bottom, ¹⁶O₂ – ¹⁸O₂ difference spectra of the oxygenated buffers in the absence of MMOH and MMOB proteins. Intensities of sMMO spectra were normalized to protein vibration. In the absence of protein, relative intensity was normalized using buffer vibrations.