X-band 3-pulse ESEEM spectra of 15N-globally labeled mitoNEET (top) and native mitoNEET (bottom). Experimental conditions: frequency 9.32 GHz, field position 344 mT, π/2 width 16 ns, τ 192 ns, initial T 64 ns, T increment 16 ns, repetition time 5 ms, temperature 12 K. (Inset) Q-band Mims ENDOR of 15N-labeled mitoNEET. The asterisk at ~ 5.9 MHz of Mims-ENDOR spectrum indicates an RF-amplifier harmonic from 1H resonances that appeared as a spectral artifact. Experimental conditions: frequency 33.922 GHz, field position 1250.8 mT (≈ g2), π/2 width 20 ns, τ 720 ns, RF-pulse width 60 μs, RF-power 250 W, repetition time 10 ms, stochastic sampling, temperature 12 K.