Characterization of the Primary Radical Pair in Reaction Centers of Heliobacillus mobilis by ¹³C Photo-CIDNP MAS NMR

Abstract

Photochemically induced dynamic nuclear polarization (photo-CIDNP) has been observed in membrane fragments of heliobacterium Heliobacillus mobilis without further isolation by (13)C magic-angle spinning (MAS) solid-state NMR under continuous illumination with white light. In the (13)C photo-CIDNP MAS NMR spectra of heliobacterial membrane fragments, two sets of signals are observed, allowing characterization of the primary radical pair. One set, showing enhanced absorptive (positive) signals, arises from the BChl g donor, while the set of emissive (negative) signals is assigned to the 8(1)-hydroxy Chl a acceptor. Hence, under these sample conditions, both donor and acceptor sides are either monomeric or composed of identical cofactors. The occurrence of the differential relaxation (DR) mechanism suggests a donor triplet lifetime in the microsecond range. It appears that the occurrence of the solid-state photo-CIDNP effect is a general feature of primary radical pairs in natural photosynthesis.

Nanosecond-Flash 15N Photo-CIDNP MAS NMR on Reaction Centers of Rhodobacter sphaeroides R26

“…Donors have been found to be monomers, asymmetric dimers and symmetric dimers [56]. Also the involvement of the protein matrix in the donor structure has been proposed [12,15]. Two parallel branches have been proposed on the acceptor site [57].…”

“…It has been shown that high-quality photo-CIDNP data can be obtained from membrane-bound RCs [12] and even cells [9]. Hence, even if an RC isolation is not feasible, photo-CIDNP MAS NMR still can be applied.…”

“…Meanwhile, the effect has been observed under continuous irradiation of the sample by 13 C and 15 N MAS NMR in bacterial RCs of Rhodobacter (Rb.) sphaeroides WT [8] and R26 [9], Rhodopseudomonas acidophila [10], Chlorobium tepidum [11] and Heliobacillus mobilis [12] as well as in RCs of plant photosystems I and II [13][14][15]. Solidstate photo-CIDNP effects were also observed on ketones in organic phase [16].…”

Photo-CIDNP in the Reaction Center of the Diatom Cyclotella meneghiniana Observed by 13C MAS NMR

“…PCC 6803 [17] -a cyanobacterium -and the firmicute Heliobacillus mobilis. [18] Additionally, there are two more bacterial phyla which contain phototrophic members: chloroflexi and acidobacteria. [19] From both phyla, no experiments with photo-CIDNP MAS NMR have been reported so far.…”

Photochemically Induced Dynamic Nuclear Polarization Observed by Solid-State NMR in a Uniformly 13C-Isotope-Labeled Photosynthetic Reaction Center

“…frozen natural photosynthetic systems, where it allows for detailed functional analysis 4,5,6,3,7 , as well as a blue-light photoreceptor LOV1-C57S 8,9 . Since all natural photosynthetic systems tested have shown the effect, it has been proposed that the solid-state photo-CIDNP effect is related to the unsurpassed efficiency of natural photosynthetic electron transfer 10 .…”