Figure 3.

The NMR spectra of¹⁹F-T103C and¹⁹F-T333C are sensitive to the heme spin state. The spin state of the CYP121 heme is modulated by the ionic strength of the buffer solution (A), and the high-salt to low-salt difference spectrum is shown in (B). Salt modulation of the spin state was then used to confirm the presence of paramagnetically induced pseudo-contact shifts in ¹⁹F-NMR spectra of each proximal surface probe. At 50 mM potassium phosphate, both spectra contain two primary resonances (panels C and D). For each label, acquisitions in the presence of increasing NaCl (which promotes low spin) decrease the upfield resonance.