Apurinic/apyrimidinic endonuclease 1 has major impact in prevention of suicidal covalent DNA-protein crosslink with apurinic/apyrimidinic site in cellular extracts.

DNA-protein crosslinks (DPC) are common DNA lesions induced by various external and endogenous agents. One of the sources of DPC is the apurinic/apyrimidinic site (AP site) and proteins interacting with it. Some proteins possessing AP lyase activity form covalent complexes with AP site-containing DNA without borohydride reduction (suicidal crosslinks). We have shown earlier that tyrosyl-DNA phosphodiesterase 1 (TDP1) but not AP endonuclease 1 (APE1) is able to remove intact OGG1 from protein-DNA adducts, whereas APE1 is able to prevent the formation of DPC by hydrolyzing the AP site. Here we demonstrate that TDP1 can remove intact PARP2 but not XRCC1 from covalent enzyme-DNA adducts with AP-DNA formed in the absence of APE1. We also analyzed an impact of APE1 and TDP1 on the efficiency of DPC formation in APE1-/- or TDP1-/- cell extracts. Our data revealed that APE1 depletion leads to increased levels of PARP1-DNA crosslinks, whereas TDP1 deficiency has little effect on DPC formation.

Oscillatory and Relaxation Study of the Interfacial Rheology of Star Polymers with Low-Grafting-Density PEO Arms and Hydrophobic Poly(divinylbenzene) Cores.

Star polymers have been gaining interest due to their tunable properties. They have been used as effective stabilizers for Pickering emulsions. Herein, star polymers were synthesized via activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). Poly(ethylene oxide) (PEO) with terminal α-bromoisobutyrate ATRP functionality was used as a macroinitiator and divinylbenzene as a crosslinker for the arm-first star synthesis. Stars with PEO arms with a molar mass of either 2 or 5 kDa had a relatively low density of grafted chains, i.e., ca. 0.25 chain/nm2. The properties of PEO stars adsorbed at oil-water interfaces were investigated using interfacial tension and interfacial rheology. The magnitude of interfacial tensions at oil-water interfaces depends on the nature of the oil phase, being lower at the m-xylene/water interface than at the n-dodecane/water interface. Small differences were observed for stars with different molecular weights of PEO arms. The overall behavior of PEO stars adsorbed at an interface can be considered as an intermediate between a particle and a linear/branched polymer. Obtained results offer an important insight into the interfacial rheology of PEO star polymers in the context of their application as stabilizers for Pickering emulsions.

The first case of microsporidiosis in Paramecium.

A new microsporidian species, Globosporidium paramecii gen. nov., sp. nov., from Paramecium primaurelia is described on the basis of morphology, fine structure, and SSU rRNA gene sequence. This is the first case of microsporidiosis in Paramecium reported so far. All observed stages of the life cycle are monokaryotic. The parasites develop in the cytoplasm, at least some part of the population in endoplasmic reticulum and its derivates. Meronts divide by binary fission. Sporogonial plasmodium divides by rosette-like budding. Early sporoblasts demonstrate a well-developed exospore forming blister-like structures. Spores with distinctive spherical shape are dimorphic in size (3.7 ± 0.2 and 1.9 ± 0.2 µm). Both types of spores are characterized by a thin endospore, a short isofilar polar tube making one incomplete coil, a bipartite polaroplast, and a large posterior vacuole. Experimental infection was successful for 5 of 10 tested strains of the Paramecium aurelia species complex. All susceptible strains belong to closely related P. primaurelia and P. pentaurelia species. Phylogenetic analysis placed the new species in the Clade 4 of Microsporidia and revealed its close relationship to Euplotespora binucleata (a microsporidium from the ciliate Euplotes woodruffi), to Helmichia lacustris and Mrazekia macrocyclopis, microsporidia from aquatic invertebrates.

The cell wall of the filamentous anoxygenic phototrophic bacterium Oscillochloris trichoides.

The filamentous anoxygenic phototrophic bacterium Oscillochloris trichoides DG-6 has been studied, and it has been shown that there are no lipopolysaccharides on the cell surface. Fatty acids hydroxylated at the C3 position, amino sugars and phosphate-containing compounds characteristic of lipid A have also not been found. The genes encoding for proteins responsible for the synthesis of lipopolysaccharides and the genes for the transport system, usually localized in the outer membrane of Gram-negative bacteria, have not been detected in the genome. The rigid layer of the cell wall contains a peptidoglycan consisting of alanine, glutamine, ornithine and glycine, in the respective ratio 1.8 : 1.5 : 1.0 : 0.6. Thus, the investigated bacterium, Osc. trichoides, is a monoderm. The cell wall also contains a branched α-1,4-d-glucan with a repeating unit consisting of glucose residues linked by α-1→4 bonds (α-1→6 at the branching sites). Such polymers have not previously been reported in phototrophic bacteria.

Poly(ADP-ribose) polymerases covalently modify strand break termini in DNA fragments in vitro.

Poly(ADP-ribose) polymerases (PARPs/ARTDs) use nicotinamide adenine dinucleotide (NAD+) to catalyse the synthesis of a long branched poly(ADP-ribose) polymer (PAR) attached to the acceptor amino acid residues of nuclear proteins. PARPs act on single- and double-stranded DNA breaks by recruiting DNA repair factors. Here, in in vitro biochemical experiments, we found that the mammalian PARP1 and PARP2 proteins can directly ADP-ribosylate the termini of DNA oligonucleotides. PARP1 preferentially catalysed covalent attachment of ADP-ribose units to the ends of recessed DNA duplexes containing 3'-cordycepin, 5'- and 3'-phosphate and also to 5'-phosphate of a single-stranded oligonucleotide. PARP2 preferentially ADP-ribosylated the nicked/gapped DNA duplexes containing 5'-phosphate at the double-stranded termini. PAR glycohydrolase (PARG) restored native DNA structure by hydrolysing PAR-DNA adducts generated by PARP1 and PARP2. Biochemical and mass spectrometry analyses of the adducts suggested that PARPs utilise DNA termini as an alternative to 2'-hydroxyl of ADP-ribose and protein acceptor residues to catalyse PAR chain initiation either via the 2',1″-O-glycosidic ribose-ribose bond or via phosphodiester bond formation between C1' of ADP-ribose and the phosphate of a terminal deoxyribonucleotide. This new type of post-replicative modification of DNA provides novel insights into the molecular mechanisms underlying biological phenomena of ADP-ribosylation mediated by PARPs.

Decreased Cathepsin K Plasma Level may Reflect an Association of Osteopoenia/Osteoporosis with Coronary Atherosclerosis and Coronary Artery Calcification in Male Patients with Stable Angina.

BACKGROUND: The aim of this study was to evaluate the plasma levels of bone turnover markers (BTMs) in male patients with stable angina depending on the bone mineral density (BMD), coronary atherosclerosis (CA) and coronary artery calcification (CAC). METHODS: We recruited 112 males with verified stable angina. All the patients underwent coronary angiography, multislice spiral computed tomography, and dual-energy X-ray absorptiometry. Plasma levels of BTMs were measured by enzyme-linked immunosorbent assay. RESULTS: Osteopoenia and osteoporosis were reported in 90 (80.4%) and 34 (30.4%) patients, respectively. Multivessel coronary artery disease, severe CA and CAC, decreased cathepsin K plasma level, and increased osteocalcin plasma level were significantly more prevalent in patients with osteopoenia/osteoporosis compared to the subjects with normal BMD. Patients with severe CA and CAC had significantly reduced cathepsin K plasma levels. CONCLUSIONS: We revealed a significant association of osteopoenia/osteoporosis with severe CA and CAC in males with stable angina. Cathepsin K and osteocalcin plasma levels may be suggested as the significant markers of osteopoenia/osteoporosis. In addition, cathepsin K plasma level can be also a valuable marker of severe CA and CAC.

Reconstruction of bacteriochlorophyll biosynthesis pathways in the filamentous anoxygenic phototrophic bacterium Oscillochloris trichoides DG-6 and evolution of anoxygenic phototrophs of the order Chloroflexales.

It is commonly accepted that green filamentous anoxygenic phototrophic (FAP) bacteria are the most ancient representatives of phototrophic micro-organisms. Modern FAPs belonging to the order Chloroflexales are divided into two suborders: Chloroflexineae and Roseiflexineae. Representatives of Roseiflexineae lack chlorosomes and synthesize bacteriochlorophyll a, whereas those of Chloroflexineae synthesize bacteriochlorophylls a and c and utilize chlorosomes for light harvesting. Though they constitute a small number of species, FAPs are quite diverse in their physiology. This bacterial group includes autotrophs and heterotrophs, thermophiles and mesophiles, aerobes and anaerobes, occupying both freshwater and halophilic environments. The anaerobic mesophilic autotroph Oscillochloris trichoides DG-6 is still not well studied in its physiology, and its evolutionary origin remains unclear. The goals of this study included identification of the reaction centre type of O. trichoides DG-6, reconstruction of its bacteriochlorophyll biosynthesis pathways, and determination of its evolutionary relationships with other FAPs. By enzymic and genomic analysis, the presence of RCII in O. trichoides DG-6 was demonstrated and the complete gene set involved in biosynthesis of bacteriochlorophylls a and c was established. We found that the bacteriochlorophyll gene sets differed between aerobic and anaerobic FAPs. The aerobic FAP genomes code oxygen-dependent AcsF cyclases, but lack the bchQ/bchR genes, which have been associated with adaptation to low light conditions in the anaerobic FAPs. A scenario of evolution of FAPs belonging to the order Chloroflexales is proposed.

Design of a New Fluorescent Oligonucleotide-Based Assay for a Highly Specific Real-Time Detection of Apurinic/Apyrimidinic Site Cleavage by Tyrosyl-DNA Phosphodiesterase 1.

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) promotes catalytic scission of a phosphodiester bond between the 3'-end of DNA and the hydroxyl group of a tyrosine residue, as well as cleaving off a variety of other 3'-terminal phosphate-linked DNA substituents. We have shown recently that Tdp1 can initiate an apurinic/apyrimidinic (AP) site repair pathway that is independent from the one mediated by AP endonuclease 1 (APE1). Until recently, there was no method available of tracking the AP-site cleaving activity of Tdp1 by real-time fluorescence assay. In the present study we demonstrate a highly specific real-time detection of the AP-site cleaving activity of Tdp1 which allows one to distinguish it from the activity of APE1 by using a short hairpin oligonucleotide with a 1,12-dodecanediol loop, a 5'-fluorophore, and a 3'-quencher. Specific phosphodiesterase activity of Tdp1, which is usually able to remove quencher from the 3'-end of DNA, was suppressed in our approach by introducing a noncleavable phosphate group mimic between the 3'-end and the quencher. As a nondigestible 3'-phosphate analogue, we have used a new uncharged tetramethyl phosphoryl guanidine (Tmg) group, which is resistant to 3'-phosphodiesterase cleavage.

Anti-Arrhenius cleavage of covalent bonds in bottlebrush macromolecules on substrate.

Spontaneous degradation of bottlebrush macromolecules on aqueous substrates was monitored by atomic force microscopy. Scission of C ─ C covalent bonds in the brush backbone occurred due to steric repulsion between the adsorbed side chains, which generated bond tension on the order of several nano-Newtons. Unlike conventional chemical reactions, the rate of bond scission was shown to decrease with temperature. This apparent anti-Arrhenius behavior was caused by a decrease in the surface energy of the underlying substrate upon heating, which results in a corresponding decrease of bond tension in the adsorbed macromolecules. Even though the tension dropped minimally from 2.16 to 1.89 nN, this was sufficient to overpower the increase in the thermal energy (k(B)T) in the Arrhenius equation. The rate constant of the bond-scission reaction was measured as a function of temperature and surface energy. Fitting the experimental data by a perturbed Morse potential V = V(0)(1 - e(-ßx))(2) - fx, we determined the depth and width of the potential to be V(0) = 141 ± 19 kJ/mol and ß(-1) = 0.18 ± 0.03 Å, respectively. Whereas the V(0) value is in reasonable agreement with the activation energy E(a) = 80-220 kJ/mol of mechanical and thermal degradation of organic polymers, it is significantly lower than the dissociation energy of a C ─ C bond D(e) = 350 kJ/mol. Moreover, the force constant K(x) = 2ß(2)V(0) = 1.45 ± 0.36 kN/m of a strained bottlebrush along its backbone is markedly larger than the force constant of a C ─ C bond K(l) = 0.44 kN/m, which is attributed to additional stiffness due to deformation of the side chains.

Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes.

The simultaneous, concerted transfer of electrons and protons--electron-proton transfer (EPT)--is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H(+) is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck-Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated (+)H ─ B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.

New stands of species of the Paramecium aurelia complex in Africa and Europe.

The relevance of geographical distribution and the roles of dispersal and spatial isolation during the speciation of microorganisms are nowadays of great interest. The Paramecium aurelia species complex is a perfect model system to explore these questions given its long history as a study subject and broad distribution. However, the world-wide distribution of the Paramecium aurelia complex (Ciliophora, Protista) still needs study, e.g., sampling in the southern hemisphere has been quite limited, while Europe has been investigated for years, with the majority of aurelia species isolated from here. Recently, new stands of species of the P. aurelia complex were found in southern Europe (Malta, Bulgaria, Cyprus) and in the Czech Republic (P. primaurelia, P. triaurelia, P. octaurelia). In Africa (Republic of South Africa), new stands of P. primaurelia, P. triaurelia, and P. octaurelia were found. Interestingly, the rare species P. triaurelia, and P. octaurelia were found to co-occur both in South Africa (SA 13) and the Czech Republic (CKV 8). Newly established strains were identified to species by crossing with the test strains (the reference strains for the particular species).

Microfluidic fabrication of stable gas-filled microcapsules for acoustic contrast enhancement.

We introduce a facile approach for the production of gas-filled microcapsules designed to withstand high pressures. We exploit microfluidics to fabricate water-filled microcapsules that are then externally triggered to become gas-filled, thus making them more echogenic. In addition, the gas-filled microcapsules have a solid polymer shell making them resistant to pressure-induced buckling, which makes them more mechanically robust than traditional prestabilized microbubbles; this should increase the potential of their utility for acoustic imaging of porous media with high hydrostatic pressures such as oil reservoirs.

Oribatid mites (Acari, Oribatida) of plain area of the Southern European Russia.

The paper is devoted to the fauna of oribatid mites (Acari: Oribatida) mostly of a plain area of the Southern European Russia. The most updated taxonomic list of oribatid mite taxa compiled from the original authors' data collected after sam- pling soil, nests and plumage of birds, as well as published sources is presented. It includes 256 species of oribatid mites belonging to 72 families. Twenty species and one family of oribatid mites are recorded for the first time at the research territory. The abundance of mites in the soil is also provided for selected species.

Holospora-like bacteria "Candidatus Gortzia yakutica" and Preeria caryophila: Ultrastructure, promiscuity, and biogeography of the symbionts.

Two already known representatives of Holospora-like bacteria, "Candidatus Gortzia yakutica" from Paramecium putrinum and Preeria caryophila, originally retrieved from the Paramecium aurelia complex, were found in new hosts: Paramecium nephridiatum and Paramecium polycaryum, respectively. In the present study, these bacteria were investigated using morphological and molecular methods. For "Ca. G. yakutica", the first details of the electron microscopic structure in the main and new hosts were provided. Regarding Pr. caryophila, the ultrastructural description of this species was implemented by several features previously unknown, such as the so called "membrane cluster" dividing periplasm from cytoplasm and fine composition of infectious forms before and during its releasing from the infected macronucleus. The new combinations of these Holospora-like bacteria with ciliate hosts were discussed from biogeographical and ecological points of view. Host specificity of symbionts as a general paradigm was critically reviewed as well.

Prospects for the use of macrocyclic photosensitizers for inactivation of SARS-CoV-2: selection of compounds leaders based on the molecular docking data.

The treatment of coronavirus COVID-19, like other viral diseases, is currently underdeveloped. This fact necessitates the search for new drugs and treatment methods that will effectively disrupt the life cycle of the virus. A big problem in the therapy of viral diseases is the ability of viruses to evade the host's immune response. We suppose that the search for drugs that can change the evasiveness of the virus from the immune response of the host is a very promising strategy, as it can help the body to cope with the infection. Protein SARS-CoV-2 ORF8 is one of the key proteins that can suppress antiviral immunity. This paper considers the available information on the structure and functioning of ORF8, as well as the results of molecular docking of ORF8 to a wide range of tetrapyrrole macroheterocyclic compounds capable of generating reactive oxygen species upon photoirradiation. This principle of photoinactivation of biosubstrates underlies the methods of photodynamic therapy of cancer. Application of photoinactivation of drug-resistant forms of bacteria and some viruses can be useful in the fight against COVID-19 and other viral infections. In this work, the structure of ORF8 complexes with macrocyclic compounds is considered in detail, the dependence of their binding affinity on the nature of macrocycles and the nature of peripheral substituents is analyzed and spectral studies of the binding of ORF8 to chlorin is performed. This paper is a part of a large project to investigate the possibility of using macrocyclic compounds for the treatment of viral diseases.Communicated by Ramaswamy H. Sarma.

Cryptic Diversity in Paramecium multimicronucleatum Revealed with a Polyphasic Approach.

Paramecium (Ciliophora) systematics is well studied, and about twenty morphological species have been described. The morphological species may include several genetic species. However, molecular phylogenetic analyses revealed that the species diversity within Paramecium could be even higher and has raised a problem of cryptic species whose statuses remain uncertain. In the present study, we provide the morphological and molecular characterization of two novel Paramecium species. While Paramecium lynni n. sp., although morphologically similar to P. multimicronucleatum, is phylogenetically well separated from all other Paramecium species, Paramecium fokini n. sp. appears to be a cryptic sister species to P. multimicronucleatum. The latter two species can be distinguished only by molecular methods. The number and structure of micronuclei, traditionally utilized to discriminate species in Paramecium, vary not only between but also within each of the three studied species and, thus, cannot be considered a reliable feature for species identification. The geographic distribution of the P. multimicronucleatum and P. fokini n. sp. strains do not show defined patterns, still leaving space for a role of the geographic factor in initial speciation in Paramecium. Future findings of new Paramecium species can be predicted from the molecular data, while morphological characteristics appear to be unstable and overlapping at least in some species.

Structural features of DNA polymerases ß and λ in complex with benzo[a]pyrene-adducted DNA cause a difference in lesion tolerance.

DNA polymerases ß (Pol ß) and λ (Pol λ) belong to one structural family (X family) and possess the same enzymatic activities. Nonetheless, these enzymes have differences in their catalytic efficiency and specificity. We have previously reported that these enzymes can bypass bulky benzo[a]pyrene-DNA adducts via translesion synthesis during gap-filling reactions, although efficiency and specificity are dependent on the reaction conditions and adduct conformation. In the present study, we analyzed structural features of Pols ß and λ complexed with a gapped DNA duplex containing either cis- or trans-benzo[a]pyrene-diol epoxide-N2-dG (BP-dG) using molecular dynamics simulations. It was found that the most pronounced structural difference lies in the positioning of the trans-BP-dG residue relative to secondary structures of the protein; this dissimilarity may explain the differences between Pols ß and λ in gap-filling/translesion synthesis. In the case of Pol ß, trans-BP-dG turned out to be positioned parallel to the α-helix and ß-sheet. In the Pol λ complex, trans-BP-dG is perpendicular to the α-helix. This difference persisted throughout the molecular dynamics trajectory. Selectivity for the BP-dG isomers remained after a deletion of noncatalytic domains of Pol λ. Modeling of Pol λ or ß complexes with cis-BP-dG-containing DNA in the presence of Mn2+ either at both metal-binding sites or at the catalytic site only revealed that for both enzymes, the model of the complex containing both Mg2+ and Mn2+ is stabler than that containing two Mn2+ ions. This observation may reflect a shared property of these enzymes: the preference for Mn2+ in terms of catalysis and for Mg2+ regarding triphosphate coordination during the translesion reaction.

'Candidatus Gromoviella agglomerans', a novel intracellular Holosporaceae parasite of the ciliate Paramecium showing marked genome reduction.

Holosporales are an alphaproteobacterial lineage encompassing bacteria obligatorily associated with multiple diverse eukaryotes. For most representatives, little is known on the interactions with their hosts. In this study, we characterized a novel Holosporales symbiont of the ciliate Paramecium polycaryum. This bacterium inhabits the host cytoplasm, frequently forming quite large aggregates. Possibly due to such aggregates, host cells sometimes displayed lethal division defects. The symbiont was also able to experimentally stably infect another Paramecium polycaryum strain. The bacterium is phylogenetically related with symbionts of other ciliates and diplonemids, forming a putatively fast-evolving clade within the family Holosporaceae. Similarly to many close relatives, it presents a very small genome (<600 kbp), and, accordingly, a limited predicted metabolism, implying a heavy dependence on Paramecium, thanks also to some specialized membrane transporters. Characterized features, including the presence of specific secretion systems, are overall suggestive of a mild parasitic effect on the host. From an evolutionary perspective, a potential ancestral trend towards pronounced genome reduction and possibly linked to parasitism could be inferred, at least among fast-evolving Holosporaceae, with some lineage-specific traits. Interestingly, similar convergent features could be observed in other host-associated lineages, in particular Rickettsiales among Alphaproteobacteria.

Molecular tensile machines: intrinsic acceleration of disulfide reduction by dithiothreitol.

Significant tension on the order of 1 nN is self-generated along the backbone of bottlebrush macromolecules due to steric repulsion between densely grafted side chains. The intrinsic tension is amplified upon adsorption of bottlebrush molecules onto a substrate and increases with grafting density, side chain length, and strength of adhesion to the substrate. These molecules were employed as miniature tensile machines to study the effect of mechanical force on the kinetics of disulfide reduction by dithiothreitol (DTT). For this purpose, bottlebrush macromolecules containing a disulfide linker in the middle of the backbone were synthesized by atom transfer radical polymerization (ATRP). The scission reaction was monitored through molecular imaging by atomic force microscopy (AFM). The scission rate constant increases linearly with the concentration of DTT and exponentially with mechanical tension along the disulfide bond. Moreover, the rate constant at zero force is found to be significantly lower than the reduction rate constant in bulk solution, which suggests an acidic composition of the water surface with pH = 3.7. This work demonstrates the ability of branched macromolecules to accelerate chemical reactions at specific covalent bonds without applying an external force.

Electrostatic control of spin exchange between mobile spin-correlated radical pairs created in micellar solutions.

A series of photoinduced H-atom abstraction reactions between anthraquinone-2,6,-disulfonate, disodium salt (AQDS) and differently charged micellar substrates is presented. After a 248 nm excimer laser flash, the first excited triplet state of AQDS is rapidly formed and then quenched by abstraction of a hydrogen atom from the alkyl chain of the micelle surfactant, leading to a spin-correlated radical pair (SCRP). The SCRP is detected 500 ns after the laser flash using time-resolved (direct detection) electron paramagnetic resonance (TREPR) spectroscopy at X-band (9.5 GHz). By changing the charge on the surfactant headgroup from negative (sodium dodecyl sulfate, SDS) to positive (dodecyltrimethylammonium chloride, DTAC), TREPR spectra with different degrees of antiphase structure (APS) in their line shape were observed. The first derivative-like APS line shape is the signature of an SCRP experiencing an electron spin exchange interaction between the radical centers, which was clearly observable in DTAC micelles and absent in SDS micellar solutions. Solutions with surfactant concentrations well below the critical micelle concentration (cmc) or solutions where micellar formation had been disrupted (1:1 v/v CH(3)CN/H(2)O) also showed no APS line shapes in their TREPR spectra. These results support the conclusion that electrostatic forces between the sensitizer (AQDS) charge and the substrate (surfactant) headgroup charge are responsible for the observed effects. The results represent a new example of electrostatic control of a spin exchange interaction in mobile radical pairs.