Biochimica et Biophysica Acta-Bioenergetics最新文献

{"title":"The small membrane protein CcoS is involved in cofactor insertion into the cbb3-type cytochrome c oxidase","authors":"Juna Rauch ,&nbsp;Katharina Kurscheidt ,&nbsp;Kai-Wei Shen ,&nbsp;Andreea Andrei ,&nbsp;Noel Daum ,&nbsp;Yavuz Öztürk ,&nbsp;Frederic Melin ,&nbsp;Gunhild Layer ,&nbsp;Petra Hellwig ,&nbsp;Fevzi Daldal ,&nbsp;Hans-Georg Koch","doi":"10.1016/j.bbabio.2024.149524","DOIUrl":"10.1016/j.bbabio.2024.149524","url":null,"abstract":"<div><div>Respiratory complexes, such as cytochrome oxidases, are cofactor-containing multi-subunit protein complexes that are critically important for energy metabolism in all domains of life. Their intricate assembly strictly depends on accessory proteins, which coordinate subunit associations and cofactor deliveries. The small membrane protein CcoS was previously identified as an essential assembly factor to produce an active <em>cbb</em>₃-type cytochrome oxidase (<em>cbb</em>₃-Cox) in <em>Rhodobacter capsulatus,</em> but its function remained unknown. Here we show that the Δ<em>ccoS</em> strain assembles a heme <em>b</em> deficient <em>cbb</em>₃-Cox, in which the CcoN-CcoO subunit association is impaired. Chemical crosslinking demonstrates that CcoS interacts with the CcoN and CcoP subunits of <em>cbb</em>₃-Cox, and that it stabilizes the interaction of the Cu-chaperone SenC with <em>cbb</em>₃-Cox. CcoS lacks heme- or Cu-binding motifs, and we did not find evidence for direct heme or Cu binding; rather our data indicate that CcoS, together with SenC, coordinates heme and Cu insertion into <em>cbb</em>₃-Cox.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149524"},"PeriodicalIF":3.4,"publicationDate":"2024-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142639012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Requirement of Bacillus subtilis succinate:menaquinone oxidoreductase activity for membrane energization depends on the direction of catalysis","authors":"Natalia V. Azarkina","doi":"10.1016/j.bbabio.2024.149522","DOIUrl":"10.1016/j.bbabio.2024.149522","url":null,"abstract":"<div><div>Succinate:quinone oxidoreductases (SQR) from <em>Bacilli</em> catalyze reduction of menaquinone by succinate, as well as the reverse reaction. The direct activity is energetically unfavorable and lost upon ΔμН⁺ dissipation, thus suggesting ΔμН⁺ to be consumed during catalysis. Paradoxically, the generation of ΔμН⁺ upon fumarate reduction was never confirmed. Thus, the exact role of ΔμН⁺ in the operation of bacillary-type SQRs remained questionable. The purpose of this work was to clarify this issue.</div><div>We have described the different operating modes of the membrane-bound SQR from <em>Bacillus subtilis</em>. Tightly coupled membrane vesicles from both wild-type cells and the mutant containing cytochrome <em>bd</em> as the only terminal oxidase were studied. This made it possible to compare the respiratory chains with 2 versus 1H⁺/e⁻ stoichiometry of ΔμН⁺ generation. Direct and reverse activities of SQR were determined under either energized or deenergized conditions.</div><div>The wild-type membranes demonstrated high succinate oxidase activity very sensitive to uncoupling. On the contrary, the mutant showed extremely low succinate oxidase activity resistant to uncoupling. ΔμН⁺ generation at the cost of ATP hydrolysis restored the uncoupling sensitive succinate respiration in the mutant. Membranes of the both types effectively reduced fumarate by menaquinol. This activity was not affected by energization or uncoupling, neither it was followed by ΔμН⁺ generation.</div><div>Thus, <em>B. subtilis</em> SQR demonstrates two regimes: ΔμН⁺-coupled and not coupled. This behavior can be explained by assuming the presence of two menaquinone binding sites which drastically differ in affinity for the oxidized and reduced substrate.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149522"},"PeriodicalIF":3.4,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142632164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"In vitro photocurrents from spinach thylakoids following Mn depletion and Mn-cluster reconstitution","authors":"Roman Voloshin ,&nbsp;Maria Goncharova ,&nbsp;Sergey K. Zharmukhamedov ,&nbsp;Barry D. Bruce ,&nbsp;Suleyman I. Allakhverdiev","doi":"10.1016/j.bbabio.2024.149523","DOIUrl":"10.1016/j.bbabio.2024.149523","url":null,"abstract":"<div><div>Biohybrid devices that generate an electrical signal under the influence of light due to photochemical reactions in photosynthetic pigment-protein complexes have many prospects. On the one hand, the oxygen-evolving complex of photosystem II allows the use of ubiquitous water as a source of electrons for photoinduced electron transfer in such devices; on the other hand, it is the most vulnerable part of the photosynthetic apparatus. From the perspective of sustainable operation of bio-based hybrid devices, it is helpful to analyze how removing or modifying the Mn cluster will affect the performance of the bio-hybrid device. This work analyzed photocurrent generation in a liquid three-electrode solar cell based on manganese-depleted and reactivated thylakoid membranes. Membranes lacking Mn could not produce any significant photocurrent until manganese chloride was added. After adding MnCl₂, the cell could produce current when exposed to light. This current was about a few percent from cells with intact thylakoid membranes. However, the photoactivation procedure made it possible to restore up to 75 % of the photocurrent of cells based on intact thylakoid membranes. The main objective of this work is to answer the question about the possibility of photocurrent generation in a biohybrid system based on thylakoid membranes using artificial analogs of the native oxygen-evolving complex. Photoactivation with manganese chloride is the simplest way to obtain preparations devoid of the native Mn cluster, but capable of oxidizing water.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149523"},"PeriodicalIF":3.4,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142632161","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Finding the E-channel proton loading sites by calculating the ensemble of protonation microstates","authors":"Md. Raihan Uddin ,&nbsp;Umesh Khaniya ,&nbsp;Chitrak Gupta ,&nbsp;Junjun Mao ,&nbsp;Gehan A. Ranepura ,&nbsp;Rongmei Judy Wei ,&nbsp;Jose Ortiz-Soto ,&nbsp;Abhishek Singharoy ,&nbsp;M.R. Gunner","doi":"10.1016/j.bbabio.2024.149518","DOIUrl":"10.1016/j.bbabio.2024.149518","url":null,"abstract":"<div><div>The aerobic electron transfer chain builds a proton gradient by proton coupled electron transfer reactions through a series of proteins. Complex I is the first enzyme in the sequence. Here transfer of two electrons from NADH to quinone yields four protons pumped from the membrane N- (negative, higher pH) side to the P- (positive, lower pH) side. Protons move through three linear antiporter paths, with a few amino acids and waters providing the route; and through the <em>E</em>-channel, a complex of competing paths, with clusters of interconnected protonatable residues.</div><div>Proton loading sites (PLS) transiently bind protons as they are transported from N- to P-compartments. PLS can be individual residues or extended clusters of residues. The program MCCE uses Monte Carlos sampling to analyze the <em>E</em>-channel proton binding in equilibrium with individual Molecular Dynamics snapshots from trajectories of <em>Thermus thermuphillus</em> Complex I in the apo, quinone and quinol bound states. At pH 7, the five <em>E</em>-channel subunits (Nqo4, Nqo7, Nqo8, Nqo10, and Nqo11) take &gt;25,000 protonation microstates, each with different residues protonated. The microstate explosion is tamed by analyzing interconnected clusters of residues along the proton transfer paths. A proton is bound and released from a cluster of five coupled residues on the protein N-side and to six coupled residues in the protein center. Loaded microstates bind protons to sites closer to the P-side in the forward pumping direction. MCCE microstate analysis identifies strongly coupled proton binding amongst individual residues in the two PLS clusters.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149518"},"PeriodicalIF":3.4,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142512372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"How lipid transfer proteins and the mitochondrial membrane shape the kinetics of β-oxidation the liver","authors":"Christoff Odendaal,&nbsp;Dirk-Jan Reijngoud,&nbsp;Barbara M. Bakker","doi":"10.1016/j.bbabio.2024.149519","DOIUrl":"10.1016/j.bbabio.2024.149519","url":null,"abstract":"<div><div>The mitochondrial fatty acid β-oxidation (mFAO) is important for producing ATP under conditions of energetic stress, such as fasting and cold exposure. The regulation of this pathway is dependent on the kinetic properties of the enzymes involved. To better understand pathway behaviour, accurate enzyme kinetics is required. Setting up and interpreting such proper assays requires a good understanding of what influences the enzymes' kinetics. Often, knowing the buffer composition, pH, and temperature is considered to be sufficient.</div><div>Many mFAO enzymes are membrane-bound, however, and their kinetic properties depend on the composition and curvature of the mitochondrial membranes. These properties are, in turn, affected by metabolite concentrations, but are rarely accounted for in kinetic assays. Especially for carnitine palmitoyltransferase 1 (CPT1), this has been shown to be of great consequence.</div><div>Moreover, the enzymes of the mFAO metabolise water-insoluble acyl-CoA derivatives, which become toxic at high concentrations. <em>In vivo</em>, these are carried across the cytosol by intracellular lipid transfer proteins (iLTPs), such as the fatty-acid and acyl-CoA-binding proteins (FABP and ACBP, respectively). <em>In vitro</em>, this is often mimicked by using bovine serum albumin (BSA), which differs from the iLPTs in terms of its binding behaviour and subcellular localisation patterns.</div><div>In this review, we argue that the iLTPs and membrane properties cannot be ignored when measuring or interpreting the kinetics of mFAO enzymes. They should be considered fundamental to the activity of mFAO enzymes just as pH, buffer composition, and temperature are.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149519"},"PeriodicalIF":3.4,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142479904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lysine 204 is crucial for the antiport function of the human LAT1 transporter","authors":"Mariafrancesca Scalise ,&nbsp;Raffaella Scanga ,&nbsp;Lara Console ,&nbsp;Michele Galluccio ,&nbsp;Lorena Pochini ,&nbsp;Cesare Indiveri","doi":"10.1016/j.bbabio.2024.149520","DOIUrl":"10.1016/j.bbabio.2024.149520","url":null,"abstract":"<div><div>LAT1 (SLC7A5) catalyzes an antiport reaction of amino acids with specificity towards the essential ones. It is mainly expressed at the Blood Brain Barrier and placenta barriers, but it becomes over-expressed in virtually all human cancers even if originating from tissues with lower expression levels. The antiport reaction of LAT1 is crucial at the BBB since its inherited loss causes Autism Spectrum Disorder. We have investigated the possible molecular determinant of the antiport by site-directed mutagenesis, <em>in vitro</em> transport assay and computational analysis. Previous data indicated that mutation of K204 impairs, but does not knock-out LAT1 functionality. We have investigated the activity changes in the K204Q mutant by following the transport of [³H]-histidine, one of the major substrates, in proteoliposomes harbouring the WT or K204Q. In the mutant, the [³H]-histidine uptake and efflux are not more stimulated by the counter-substrate as they occur in the WT. Moreover, the mutation strongly decreases the substrate affinity and alters the pH dependence of K204Q. Molecular Dynamics analysis correlates well with the experimental data since it shows that substrate prematurely escapes the binding site. In addition, the K204Q shows a strongly increased mobility in those regions, transmembrane domains and random coils, involved in the transport cycle. The identified Lys residue could be responsible of the same phenomenon in those members of the SLC7 family, described as antiporters, in which it is conserved.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149520"},"PeriodicalIF":3.4,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142479905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The molecular structure of an axle-less F1-ATPase","authors":"Emily J. Furlong ,&nbsp;Ian-Blaine P. Reininger-Chatzigiannakis ,&nbsp;Yi C. Zeng ,&nbsp;Simon H.J. Brown ,&nbsp;Meghna Sobti ,&nbsp;Alastair G. Stewart","doi":"10.1016/j.bbabio.2024.149521","DOIUrl":"10.1016/j.bbabio.2024.149521","url":null,"abstract":"<div><div>F₁F_o ATP synthase is a molecular rotary motor that can generate ATP using a transmembrane proton motive force. Isolated F₁-ATPase catalytic cores can hydrolyse ATP, passing through a series of conformational states involving rotation of the central γ rotor subunit and the opening and closing of the catalytic β subunits. Cooperativity in F₁-ATPase has long thought to be conferred through the γ subunit, with three key interaction sites between the γ and β subunits being identified. Single molecule studies have demonstrated that the F₁ complexes lacking the γ axle still “rotate” and hydrolyse ATP, but with less efficiency. We solved the cryogenic electron microscopy structure of an axle-less <em>Bacillus</em> sp. PS3 F₁-ATPase. The unexpected binding-dwell conformation of the structure in combination with the observed lack of interactions between the axle-less γ and the open β subunit suggests that the complete γ subunit is important for coordinating efficient ATP binding of F₁-ATPase.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149521"},"PeriodicalIF":3.4,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142479906","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Metabolic impairments in neurodegeneration with brain iron accumulation","authors":"Agata Wydrych ,&nbsp;Barbara Pakuła ,&nbsp;Justyna Janikiewicz ,&nbsp;Aneta M. Dobosz ,&nbsp;Patrycja Jakubek-Olszewska ,&nbsp;Marta Skowrońska ,&nbsp;Iwona Kurkowska-Jastrzębska ,&nbsp;Maciej Cwyl ,&nbsp;Mariola Popielarz ,&nbsp;Paolo Pinton ,&nbsp;Barbara Zavan ,&nbsp;Agnieszka Dobrzyń ,&nbsp;Magdalena Lebiedzińska-Arciszewska ,&nbsp;Mariusz R. Więckowski","doi":"10.1016/j.bbabio.2024.149517","DOIUrl":"10.1016/j.bbabio.2024.149517","url":null,"abstract":"<div><div>Neurodegeneration with brain iron accumulation (NBIA) is a broad, heterogeneous group of rare inherited diseases (1–3 patients/1,000,000 people) characterized by progressive symptoms associated with excessive abnormal iron deposition in the brain. Approximately 15,000–20,000 individuals worldwide are estimated to be affected by NBIA. NBIA is usually associated with slowly progressive pyramidal and extrapyramidal symptoms, axonal motor neuropathy, optic nerve atrophy, cognitive impairment and neuropsychiatric disorders. To date, eleven subtypes of NBIA have been described and the most common ones include pantothenate kinase-associated neurodegeneration (PKAN), PLA2G6-associated neurodegeneration (PLAN), mitochondrial membrane protein-associated neurodegeneration (MPAN) and beta-propeller protein-associated neurodegeneration (BPAN). We present a comprehensive overview of the evidence for disturbed cellular homeostasis and metabolic alterations in NBIA variants, with a careful focus on mitochondrial bioenergetics and lipid metabolism which drives a new perspective in understanding the course of this infrequent malady.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149517"},"PeriodicalIF":3.4,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142376280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"In isolated brown adipose tissue mitochondria, UCP1 is not essential for - nor involved in - the uncoupling effects of the classical uncouplers FCCP and DNP","authors":"Irina G. Shabalina,&nbsp;Beatriz Jiménez,&nbsp;Celso Pereira Batista Sousa-Filho,&nbsp;Barbara Cannon,&nbsp;Jan Nedergaard","doi":"10.1016/j.bbabio.2024.149516","DOIUrl":"10.1016/j.bbabio.2024.149516","url":null,"abstract":"<div><div>Recent patch-clamp studies of mitoplasts have challenged the traditional view that classical chemical uncoupling (by e.g. FCCP or DNP) is due to the protonophoric property of these substances themselves. These studies instead suggest that in brown-fat mitochondria, FCCP- and DNP-induced uncoupling is mediated through activation of UCP1 (and in other tissues by activation of the adenine nucleotide transporter). These studies thus advocate an entirely new paradigm for the interpretation of standard bioenergetic experiments.</div><div>To examine whether these patch-clamp results obtained in brown-fat mitoplasts are directly transferable to classical isolated brown-fat mitochondria studies, we investigated the effects of FCCP and DNP in brown-fat mitochondria from wildtype and UCP1 KO mice, comparing the FCCP and DNP effects with those of a fatty acid (oleate), a bona fide activator of UCP1.</div><div>Whereas the sensitivity of brown-fat mitochondria to oleate was much higher in UCP1-containing than in UCP1 KO mitochondria, there was no difference in sensitivity to FCCP and DNP between these mitochondria, neither in oxygen consumption rate nor in membrane potential studies. Correspondingly, the UCP1-dependent ability of GDP to competitively inhibit activation by oleate was not seen with FCCP and DNP.</div><div>It would thus be premature to abandon the established bioenergetic interpretation of chemical uncoupler effects in classical isolated brown-fat mitochondria—and probably also generally in this type of mitochondrial study. Understanding the molecular and structural reasons for the different outcomes of mitoplast and mitochondrial studies is a challenging task.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149516"},"PeriodicalIF":3.4,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142367319","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An unusual triplet population pathway in the Reaction Centre of the Chlorophyll-d binding Photosystem I of A. marina, as revealed by a combination of TR-EPR and ODMR spectroscopies","authors":"Alessandro Agostini ,&nbsp;Andrea Calcinoni ,&nbsp;Anastasia A. Petrova ,&nbsp;Marco Bortolus ,&nbsp;Anna Paola Casazza ,&nbsp;Donatella Carbonera ,&nbsp;Stefano Santabarbara","doi":"10.1016/j.bbabio.2024.149515","DOIUrl":"10.1016/j.bbabio.2024.149515","url":null,"abstract":"<div><div>Photo-induced Chlorophyll (Chl) triplet states in the isolated Photosystem I (PSI) of <em>Acaryochloris marina</em>, that harbours Chl <em>d</em> as its main pigment, were investigated by Optically Detected Magnetic Resonance (ODMR) and Time-Resolved Electron Paramagnetic Resonance (TR-EPR), and as a function of pre-illumination of the sample under reducing redox poising. Fluorescence Detected Magnetic Resonance (FDMR) allowed resolving four Chl <em>d</em> triplet (³Chl <em>d</em>) populations (T₁-T₄) both in untreated and illuminated samples in the presence of ascorbate and <em>N</em>,<em>N</em>,<em>N</em>′,<em>N</em>′-tetramethyl-<em>p</em>-phenylenediamine (TMPD). The FDMR signals increased following the pre-illumination treatment, particularly for the T₃ and T₄ populations, which are therefore sensitive to the redox state of PSI cofactors. Microwave-induced Triplet minus Singlet (TmS) spectra were detected in the |D|-|E| resonance window of the T₃ and T₄ triplets. These showed a broad singlet bleaching centred at 740 nm and also displayed complex spectral structure with several derivative-like features, indicating that both the T₃ and T₄ ³Chl <em>d</em> populations are associated with the PSI reaction centre (RC) triplet, <span><math><msub><mmultiscripts><mi>P</mi><mprescripts></mprescripts><mrow></mrow><mn>3</mn></mmultiscripts><mn>740</mn></msub></math></span>. Parallel measurements by TR-EPR demonstrated that triplet signals observed under all conditions investigated are dominated by an electron spin polarisation (esp), which is typical of intersystem crossing, differently from what expected for recombination triplet states formed from a radical pair precursor. Moreover, stronger reductant conditions obtained by pre-illumination of the samples in the presence of dithionite and 5-methylphenazinium methyl sulfate (PMS) did not lead to a recombination triplet state esp, but rather to a decrease of the whole signal intensity. The energetics of <em>A. marina</em> PSI and the possible occurrence of distributions of cofactors redox properties are discussed in order to address the unexpected <span><math><msub><mmultiscripts><mi>P</mi><mprescripts></mprescripts><mrow></mrow><mn>3</mn></mmultiscripts><mn>740</mn></msub></math></span> esp.</div></div>","PeriodicalId":50731,"journal":{"name":"Biochimica et Biophysica Acta-Bioenergetics","volume":"1866 1","pages":"Article 149515"},"PeriodicalIF":3.4,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142331792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}