15N–1H Transfer of Light-Induced Nuclear Hyperpolarization in Frozen Photosynthetic Reaction Centers

Abstract

Recently, we have demonstrated the possibility to transfer the light-induced hyperpolarization occurring on select 13C nuclei of photosynthetic cofactors due to the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect into the proton pool via inverse 13C–1H cross-polarization Bielytskyi et al. (J Magn Reson 293: 82–91, 2018). Such approach allowed us to observe the selective response from the protons belonging to photochemically active cofactors in their native protein environment. In the present study, we demonstrate that also 15N nuclei can be used as a source of polarization in a similar type of experiments. We present the 2D photo-CIDNP 15N–1H heteronuclear correlation (HETCOR) experiment acquired on uniformly 15N-labeled quinone-blocked reaction center (RC) from Rhodobacter sphaeroides R26. Obtained 1H chemical shifts match with previously observed ones on selectively 13C-labeled RC from Rhodobacter sphaeroides WT. We expect that using 15N as a source of polarization in potential heteronuclear spin-torch experiments could be advantageous for systems where the procedure for selective 13C labeling is not yet established.