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.