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Michael R Jones

Publications and source records attributed to Michael R Jones.

At least 19 recordsLinked to original sources
PubMed2006

Lipids in photosynthetic reaction centres: structural roles and functional holes.

Photosynthetic proteins power the biosphere. Reaction centres, light harvesting antenna proteins and cytochrome b(6)f (or bc(1)) complexes are expressed at high levels, have been subjected to an intensive spectroscopic, biochemical and mutagenic analysis, and several have been characterised to an informatively high resolution by X-ray crystallography. In addition to revealing the structural basis for the transduction of light energy, X-ray crystallography has brought molecular insights into the relationships between these multicomponent membrane proteins and their lipid environment. Lipids resolved in the X-ray crystal structures of photosynthetic proteins bind light harvesting cofactors, fill intra-protein cavities through which quinones can diffuse, form an important part of the monomer-monomer interface in multimeric structures and may facilitate structural flexibility in complexes that undergo partial disassembly and repair. It has been proposed that individual lipids influence the biophysical properties of reaction centre cofactors, and so affect the rate of electron transfer through the complex. Lipids have also been shown to be important for successful crystallisation of photosynthetic proteins. Comparison of the three types of reaction centre that have been structurally characterised reveals interesting similarities in the position of bound lipids that may point towards a generic requirement to reinforce the structure of the core electron transfer domain. The crystallographic data are also providing new opportunities to find molecular explanations for observed effects of different types of lipid on the structure, mechanism and organisation of reaction centres and other photosynthetic proteins.

Binding Sites↗
PubMed2006

Kinetic analysis of the thermal stability of the photosynthetic reaction center from Rhodobacter sphaeroides.

The temperature-induced denaturation of the photosynthetic reaction center from Rhodobacter sphaeroides has been studied through the changes that occur in the absorption spectrum of the bound chromophores on heating. At elevated temperatures, the characteristic absorbance bands of the bacteriochlorins bound to the polypeptides within the reaction center are lost, and are replaced by features typical of unbound bacteriochlorophyll and bacteriopheophytin. The kinetics of the spectral changes cannot be explained by a direct conversion from the functional to the denatured form of the protein, and require the presence of at least one intermediate. Possible mechanisms for the transformation via an intermediate are examined using a global analysis of the kinetic data, and the most likely mechanism is shown to involve a reversible transformation between the native state and an off-pathway intermediate, coupled to an irreversible transformation to the denatured state. The activation energies for the transformations between the three components are calculated from the effect of temperature on the individual rate constants, and the likely structural changes of the protein during the temperature-induced transformation are discussed.

Kinetics↗
PubMed2006

Effects of colesevelam hydrochloride on low-density lipoprotein cholesterol and high-sensitivity C-reactive protein when added to statins in patients with hypercholesterolemia.

Elevated high-sensitivity C-reactive protein (hs-CRP) levels are associated with an increased risk of atherosclerotic coronary heart disease (CHD). The addition of the bile acid sequestrants, such as colesevelam hydrochloride (HCl), to statins further reduces low-density lipoprotein (LDL) cholesterol levels. However, the effects of approved cholesterol-lowering bile acid sequestrants on hs-CRP have not previously been reported. Three randomized, double-blind, placebo-controlled, parallel, 6-week clinical trials of similar design investigated the efficacy of adding colesevelam HCl to stable simvastatin, atorvastatin, or pravastatin treatment in 204 patients with primary hypercholesterolemia. The primary end point was the mean percent change in the LDL cholesterol levels. Secondary end points included the effects on other lipid parameters and hs-CRP levels. A pooled analysis showed that adding colesevelam HCl to statin therapy significantly lowered LDL cholesterol levels (21 mg/dl or 16% mean reduction from baseline, p = 0.0013, and 11 mg/dl or 9% mean reduction compared with placebo, p = 0.0003). Four times as many patients receiving colesevelam HCl plus a statin achieved a LDL cholesterol target of <100 mg/dl compared with patients receiving a statin plus placebo (39% vs 10%, respectively, p <0.0001). The incidence of mild gastrointestinal adverse effects was slightly higher in the colesevelam HCl plus statin group than in the placebo plus statin group. Finally, the differences in the change in hs-CRP levels with colesevelam HCl plus statin therapy were significant compared with the changes with placebo plus statin (median change -23%, p = 0.0069). In conclusion, this is the first report suggesting that an approved cholesterol-lowering bile acid sequestrant, specifically colesevelam HCl, decreases hs-CRP levels when added to statin therapy.

Allylamine↗
PubMed2005

Colesevelam hydrochloride does not cause maternal or fetal toxicity in rats and rabbits.

WelChol (colesevelam hydrochloride), a bile acid sequestrant for the treatment of hypercholesterolemia, was evaluated for adverse effects on reproduction and fetal development using standard preclinical tests. During gestation, Sprague-Dawley rats used in the developmental toxicity study received feed, feed/control article or feed plus 300, 1,000 or 3,000 mg/kg/day colesevelam whereas rats in the pre- and postnatal toxicity study received vehicle or 100, 300 or 1,000 mg/kg/day colesevelam via gavage. New Zealand white rabbits received control or 100, 500 or 1,000 mg/kg/day colesevelam via gavage. No deaths, premature deliveries or gross pathologic lesions were observed up to gestation day (GD) 20 for rats and GD 28 for rabbits. No significant differences in the number of pregnant animals, average litter size, percentage of viable fetuses, fetal body weights, number of corpora lutea, fetal viability, or gross malformations were observed versus controls. Pre- and postnatal effects were assessed in pregnant rats receiving 100, 300 or 1,000 mg/kg/day colesevelam from GD 6 to postpartum day 22. Gestation, parturition and lactation in F(0) generation dams were similar between treatment and control groups. Colesevelam did not affect physical or neurological development or induce gross pathological changes in F(1) generation rats. Colesevelam does not produce developmental toxicity in rats or rabbits, nor does it exhibit pre- or postnatal toxicity in rats at the tested doses.

Allylamine↗
PubMed2005

Replacement or exclusion of the B-branch bacteriopheophytin in the purple bacterial reaction centre: the H(B) cofactor is not required for assembly or core function of the Rhodobacter sphaeroides complex.

All of the membrane-embedded cofactors of the purple bacterial reaction centre have well-defined functional or structural roles, with the exception of the bacteriopheophytin (H(B)) located approximately half-way across the membrane on the so-called inactive- or B-branch of cofactors. Sequence alignments indicate that this bacteriochlorin cofactor is a conserved feature of purple bacterial reaction centres, and a pheophytin is also found at this position in the Photosystem-II reaction centre. Possible structural or functional consequences of replacing the H(B) bacteriopheophytin by bacteriochlorophyll were investigated in the Rhodobacter sphaeroides reaction centre through mutagenesis of residue Leu L185 to His (LL185H). Results from absorbance spectroscopy indicated that the LL185H mutant assembled with a bacteriochlorophyll at the H(B) position, but this did not affect the capacity of the reaction centre to support photosynthetic growth, or change the kinetics of charge separation along the A-branch of cofactors. It was also found that mutation of residue Ala M149 to Trp (AM149W) caused the reaction centre to assemble without an H(B) bacteriochlorin, demonstrating that this cofactor is not required for correct assembly of the reaction centre. The absence of a cofactor at this position did not affect the capacity of the reaction centre to support photosynthetic growth, or the kinetics of A-branch electron transfer. A combination of X-ray crystallography and FTIR difference spectroscopy confirmed that the H(B) cofactor was absent in the AM149W mutant, and that this had not produced any significant disturbance of the adjacent ubiquinol reductase (Q(B)) site. The data are discussed with respect to possible functional roles of the H(B) bacteriopheophytin, and we conclude that the reason(s) for conservation of a bacteriopheophytin cofactor at this position in purple bacterial reaction centres are likely to be different from those underlying conservation of a pheophytin at the analogous position in Photosystem-II.

Chlorophyll↗
PubMed2005

Strong effects of an individual water molecule on the rate of light-driven charge separation in the Rhodobacter sphaeroides reaction center.

The role of a water molecule (water A) located between the primary electron donor (P) and first electron acceptor bacteriochlorophyll (B(A)) in the purple bacterial reaction center was investigated by mutation of glycine M203 to leucine (GM203L). The x-ray crystal structure of the GM203L reaction center shows that the new leucine residue packs in such a way that water A is sterically excluded from the complex, but the structure of the protein-cofactor system around the mutation site is largely undisturbed. The results of absorbance and resonance Raman spectroscopy were consistent with either the removal of a hydrogen bond interaction between water A and the keto carbonyl group of B(A) or a change in the local electrostatic environment of this carbonyl group. Similarities in the spectroscopic properties and x-ray crystal structures of reaction centers with leucine and aspartic acid mutations at the M203 position suggested that the effects of a glycine to aspartic acid substitution at the M203 position can also be explained by steric exclusion of water A. In the GM203L mutant, loss of water A was accompanied by an approximately 8-fold slowing of the rate of decay of the primary donor excited state, indicating that the presence of water A is important for optimization of the rate of primary electron transfer. Possible functions of this water molecule are discussed, including a switching role in which the redox potential of the B(A) acceptor is rapidly modulated in response to oxidation of the primary electron donor.

Amino Acid Substitution↗
PubMed2005

Investigation of B-branch electron transfer by femtosecond time resolved spectroscopy in a Rhodobacter sphaeroides reaction centre that lacks the Q(A) ubiquinone.

The dynamics of electron transfer in a membrane-bound Rhodobacter sphaeroides reaction centre containing a combination of four mutations were investigated by transient absorption spectroscopy. The reaction centre, named WAAH, has a mutation that causes the reaction centre to assemble without a Q(A) ubiquinone (Ala M260 to Trp), a mutation that causes the replacement of the H(A) bacteriopheophytin with a bacteriochlorophyll (Leu M214 to His) and two mutations that remove acidic groups close to the Q(B) ubiquinone (Glu L212 to Ala and Asp L213 to Ala). Previous work has shown that the Q(B) ubiquinone is reduced by electron transfer along the so-called inactive cofactor branch (B-branch) in the WAAH reaction centre (M.C. Wakeham, M.G. Goodwin, C. McKibbin, M.R. Jones, Photo-accumulation of the P(+)Q(B)(-) radical pair state in purple bacterial reaction centres that lack the Q(A) ubiquinone, FEBS Letters 540 (2003) 234-240). In the present study the dynamics of electron transfer in the membrane-bound WAAH reaction centre were studied by femtosecond transient absorption spectroscopy, and the data analysed using a compartmental model. The analysis indicates that the yield of Q(B) reduction via the B-branch is approximately 8% in the WAAH reaction centre, consistent with results from millisecond time-scale kinetic spectroscopy. Possible contributions to this yield of the constituent mutations in the WAAH reaction centre and the membrane environment of the complex are discussed.

Electron Transport↗
PubMed2005

On the role of basic residues in adapting the reaction centre-LH1 complex for growth at elevated temperatures in purple bacteria.

The purple photosynthetic bacterium Thermochromatium tepidum is a moderate thermophile, with a growth optimum of 48-50 degrees C. The X-ray crystal structure of the reaction centre from this organism has been determined, and compared with that from mesophilic bacteria such as Blastochloris viridis and Rhodobacter sphaeroides (Nogi T et al. (2000) Proc Natl Acad Sci USA 97: 13561-13566). Structural features that could contribute to the enhanced thermal stability of the Thermochromatium tepidum reaction centre were discussed, including three arginine residues exposed at the periplasmic side of the membrane that are not present in reaction centres from mesophilic organisms, and potentially could increase the affinity of the complex for the surrounding membrane. In the present report these arginine residues, plus a histidine identified from an extensive sequence alignment, were engineered into structurally homologous positions in the Rhodobacter sphaeroides reaction centre, and the effect on the thermal stability of the Rhodobacter sphaeroides complex was examined. We find that these residues do not enhance the thermal stability of the reaction centre, as assessed by absorbance spectroscopy of the bacteriochlorin cofactors in membrane-bound reaction centres. Possible roles of these residues in the Thermochromatium tepidum reaction centre are discussed, and it is proposed that they facilitate stronger binding of the reaction centre to the encircling LH1 antenna complex, through ionic interactions with acidic residues at the C-terminal end of the LH1 alpha-polypeptide. Such an interaction could enhance the stability of the so-called 'RC-LH1 core' complex that is formed between the reaction centre and the LH1 antenna, and which represents the minimal functional photosynthetic unit in all known purple photosynthetic bacteria. Stronger bonding interactions between the two complexes could also contribute to an increase in the rigidity of the photosynthetic membrane in Thermochromatium tepidum, in accord with the general finding that the cytoplasmic membrane from thermophilic eubacteria is less fluid than its counterpart in mesophilic bacteria.

Cell Proliferation↗
PubMed2005

Proteins, chlorophylls and lipids: X-ray analysis of a three-way relationship.

Photosynthetic reaction centres and light harvesting complexes have been at the forefront of crystallographic studies of integral membrane proteins. In recent years, there have been spectacular advances in our understanding of the structure of (bacterio)chlorophyll-containing membrane proteins from oxygenic and anoxygenic phototrophs. In these complex structures, the protein scaffold encases different combinations of cofactors and interacts with several tightly bound lipid species that play a variety of hitherto unrecognized structural roles. Some of these lipids have relevance to the physiological function of the protein, whereas others are important for the formation of highly ordered crystals. The first site-directed mutagenesis studies of individual lipid binding sites have now underlined the importance of the lipid component for the structural stability of protein-cofactor-lipid complexes.

Bacterial Proteins↗
PubMed2004

Characterization of the bonding interactions of Q(B) upon photoreduction via A-branch or B-branch electron transfer in mutant reaction centers from Rhodobacter sphaeroides.

In Rhodobacter sphaeroides reaction centers (RCs) containing the mutation Ala M260 to Trp (AM260W), transmembrane electron transfer along the full-length of the A-branch of cofactors is prevented by the loss of the Q(A) ubiquinone, but it is possible to generate the radical pair P(+)H(A)(-) by A-branch electron transfer or the radical pair P(+)Q(B)(-) by B-branch electron transfer. In the present study, FTIR spectroscopy was used to provide direct evidence for the complete absence of the Q(A) ubiquinone in mutant RCs with the AM260W mutation. Light-induced FTIR difference spectroscopy of isolated RCs was also used to probe the neutral Q(B) and the semiquinone Q(B)(-) states in two B-branch active mutants, a double AM260W-LM214H mutant, denoted WH, and a quadruple mutant, denoted WAAH, in which the AM260W, LM214H, and EL212A-DL213A mutations were combined. The data were compared to those obtained with wild-type (Wt) RCs and the double EL212A-DL213A (denoted AA) mutant which exhibit the usual A-branch electron transfer to Q(B). The Q(B)(-)/Q(B) spectrum of the WH mutant is very close to that of Wt RCs indicating similar bonding interactions of Q(B) and Q(B)(-) with the protein in both RCs. The Q(B)(-)/Q(B) spectra of the AA and WAAH mutants are also closely related to one another, but are very different to that of the Wt complex. Isotope-edited IR fingerprint spectra were obtained for the AA and WAAH mutants reconstituted with site-specific (13)C-labeled ubiquinone. Whilst perturbations of the interactions of the semiquinone Q(B)(-) with the protein are observed in the AA and WAAH mutants, the FTIR data show that the bonding interaction of neutral Q(B) in these two mutants are essentially the same as those for Wt RCs. Therefore, it is concluded that Q(B) occupies the same binding position proximal to the non-heme iron prior to reduction by either A-branch or B-branch electron transfer.

Amino Acid Substitution↗
PubMed2004

Formation of a semiquinone at the QB site by A- or B-branch electron transfer in the reaction center from Rhodobacter sphaeroides.

In Rhodobacter sphaeroides reaction centers containing the mutation Ala M260 to Trp (AM260W), transmembrane electron transfer along the A-branch of cofactors is prevented by the loss of the QA ubiquinone. Reaction centers that contain this AM260W mutation are proposed to photoaccumulate the P(+)QB- radical pair following transmembrane electron transfer along the B-branch of cofactors (Wakeham, M. C., Goodwin, M. G., McKibbin, C., and Jones, M. R. (2003) Photoaccumulation of the P(+)QB- radical pair state in purple bacterial reaction centers that lack the QA ubiquinone. FEBS Lett. 540, 234-240). The yield of the P(+)QB- state appears to depend upon which additional mutations are present. In the present paper, Fourier transform infrared (FTIR) difference spectroscopy was used to demonstrate that photooxidation of the reaction center's primary donor in QA-deficient reaction centers results in formation of a semiquinone at the QB site by B-branch electron transfer. Reduction of QB by the B-branch pathway still occurs at 100 K, with a yield of approximately 10% relative to that at room temperature, in contrast to the QA- to QB reaction in the wild-type reaction center, which is not active at cryogenic temperatures. These FTIR results suggest that the conformational changes that "gate" the QA- to QB reaction do not necessarily have the same influence on QB reduction when the electron donor is the HB anion, at least in a minority of reaction centers.

Alanine↗
PubMed2004

Disruption of a specific molecular interaction with a bound lipid affects the thermal stability of the purple bacterial reaction centre.

Relatively little is known about the functions of specific molecular interactions between membrane proteins and membrane lipids. The structural and functional consequences of disrupting a previously identified interaction between a molecule of the diacidic lipid cardiolipin and the purple bacterial reaction centre were examined. Mutagenesis of a highly conserved arginine (M267) that is responsible for binding the head-group of the cardiolipin (to leucine) did not affect the rate of photosynthetic growth, the functional properties of the reaction centre, or the X-ray crystal structure of the complex (determined to a resolution of 2.8 A). However, the thermal stability of the protein was compromised by this mutation, part of the reaction centre population showing an approximately 5 degrees C decrease in melting temperature in response to the arginine to leucine mutation. The crystallised mutant reaction centre also no longer bound detectable amounts of cardiolipin at this site. Taken together, these observations suggest that this particular protein-lipid interaction contributes to the thermal stability of the complex, at least when in detergent micelles. These findings are discussed in the light of proposals concerning the unfolding processes that occur when membrane proteins are heated, and we propose that one function of the cardiolipin is to stabilise the interaction between adjacent membrane-spanning alpha-helices in a region where there are no direct protein-protein interactions.

Calorimetry, Differential Scanning↗
PubMed2004

Carotid angioplasty and stenting versus carotid endarterectomy for treatment of asymptomatic carotid stenosis: a randomized trial in a community hospital.

OBJECTIVE: Carotid endarterectomy (CEA) is effective in reducing the risk of stroke in individuals with more than 60% carotid stenosis. Carotid angioplasty and stenting (CAS) has been proffered as effective and used in treating individuals with asymptomatic carotid stenosis despite the absence of proven clinical equivalency. This randomized trial was designed to explore the hypothesis that CAS is equivalent to CEA for treating asymptomatic carotid stenosis. METHODS: A total of 85 individuals presenting with asymptomatic carotid stenosis of more than 80% were selected randomly for CAS or CEA and followed up for 48 months. RESULTS: Stenosis decreased to an average of 5% after CAS. The patency of the reconstructed artery remained satisfactory regardless of the technique, as determined by carotid ultrasonography. No major complications such as cerebral ischemia or death occurred. Procedural complications associated with CAS (n = 5) were hypotension and/or bradycardia; those concomitant with CEA (n = 3) were cervical nerve injury or complications related to general anesthesia (n = 4). Both procedures were well tolerated in the context of pain and discomfort. Hospital stay was similar in the two groups (mean, 1.1 versus 1.2 d). The occurrence of complications associated with CAS or CEA prolonged hospitalization by 3 days (mean, 4.0 versus 4.5 d). Return to full activity was achieved within 1 week by more than 85% of patients; all returned to their usual lifestyle by 2 weeks. Although hospital charges were slightly higher for CAS, costs were similar. CONCLUSION: CAS and CEA may be equally effective and safe in treating individuals with asymptomatic carotid stenosis.

Aged↗
PubMed2004

Effect of colesevelam HCl on single-dose fenofibrate pharmacokinetics.

OBJECTIVE: The primary aim of this study was to determine whether there is an effect of colesevelam HCl (WelChol; Sankyo Pharma Inc., Parsippany, NJ, USA) on fenofibric acid (active metabolite of fenofibrate, TriCor, Abbott Laboratories, North Chicago, IL, USA) pharmacokinetics following single-dose fenofibrate when colesevelam HCl and fenofibrate are administered concomitantly, or when colesevelam HCl is administered 4 hours following fenofibrate therapy. METHODS: Thirty healthy volunteers were enrolled in a randomised, open-label, three-way crossover, drug interaction study. Subjects received one of three treatments at each of three dose administration periods: (i) treatment A -- fenofibrate 160 mg plus colesevelam HCl 3750 mg (6 x 625 mg tablets) administered with breakfast; (ii) treatment B -- fenofibrate 160 mg administered with breakfast, followed 4 hours later by colesevelam HCl 3750 mg (6 x 625 mg tablets) administered with lunch; or (iii) treatment C -- fenofibrate 160 mg administered with breakfast. Treatments were separated by a 10-day washout period. Blood samples were collected at predetermined time intervals, both before and after drug administration. Plasma concentrations of fenofibrate and fenofibric acid were measured using a validated liquid chromatography/mass spectroscopy/mass spectroscopy method. RESULTS: Area under the concentration-time curve (AUC) from time zero to the timepoint of the lowest quantifiable concentration (AUCt), AUC from time zero to infinity (AUCinfinity) and maximum plasma concentration (Cmax) for fenofibric acid were 92.1%, 93.9% and 79.8%, respectively, of control values when colesevelam HCl and fenofibrate were coadministered with breakfast; and 91.9%, 93.9% and 99.1%, respectively, when fenofibrate was administered followed 4 hours later by administration of colesevelam HCl. The 90% confidence intervals for the ratios of geometric means for AUCt, AUCinfinity and Cmax comparing the three treatments were contained within the 80-125% equivalence range, with the exception of Cmax for treatment A. Coadministration of fenofibrate with colesevelam HCl resulted in an approximate 20% reduction in Cmax of the active metabolite (fenofibric acid). There were no significant differences in the time to Cmax, elimination rate constant or elimination half-life between any of the treatment groups. CONCLUSIONS: Colesevelam HCl had no significant effect on fenofibrate bioavailability when administered either concomitantly with fenofibrate or 4 hours after fenofibrate.

Adult↗
PubMed2004

Erosion of a B-Lynch suture through the uterine wall: a case report.

BACKGROUND: The B-Lynch uterine suture brace has been used for the surgical treatment of postpartum hemorrhage. To date, no complications of this procedure have been reported. We describe B-Lynch suture erosion through the uterine wall identified at a 6-week postpartum visit. CASE: A 19-year-old primigravida underwent a primary low transverse cesarean section at term for arrest of descent. The surgery was complicated by postpartum hemorrhage secondary to uterine atony unresponsive to medical management. The patient underwent successful placement of a B-Lynch suture using delayed, absorbable suture for control of the hemorrhage and had an uneventful postoperative course. At her 6-week postpartum examination, she was found to have the suture protruding from the uterine cervical os. The suture was removed in its entirety without difficulty. Follow-up sonohysterography at 6 months identified a small defect in the anterior wall of the lower uterine segment, corresponding to the probable site of suture erosion. CONCLUSION: Erosion of suture through the uterine wall can be a complication of the B-Lynch uterine suture brace. Delayed, absorbable suture is less desirable than absorbable suture for this procedure due to the risk of erosion through the uterine wall.

Adult↗
PubMed2003

Acquisition of photosynthetic capacity by a reaction centre that lacks the Q(A) ubiquinone; possible insights into the evolution of reaction centres?

A photosynthetically impaired strain of Rhodobacter sphaeroides containing reaction centres with an alanine to tryptophan mutation at residue 260 of the M-polypeptide (AM260W) was incubated under photosynthetic growth conditions. This incubation produced photosynthetically competent strains containing suppressor mutations that changed residue M260 to glycine or cysteine. Spectroscopic analysis demonstrated that the loss of the Q(A) ubiquinone seen in the original AM260W mutant was reversed in the suppressor mutants. In the mutant where Trp M260 was replaced by Cys, the rate of reduction of the Q(A) ubiquinone by the adjacent (H(A)) bacteriopheophytin was reduced by three-fold. The findings of the experiment are discussed in light of the X-ray crystal structures of the wild-type and AM260W reaction centres, and the possible implications for the evolution of reaction centres as bioenergetic complexes are considered.

Crystallography, X-Ray↗
PubMed2003

Photo-accumulation of the P+QB- radical pair state in purple bacterial reaction centres that lack the QA ubiquinone.

Photo-excitation of membrane-bound Rhodobacter sphaeroides reaction centres containing the mutation Ala M260 to Trp (AM260W) resulted in the accumulation of a radical pair state involving the photo-oxidised primary electron donor (P). This state had a lifetime of hundreds of milliseconds and its formation was inhibited by stigmatellin. The absence of the Q(A) ubiquinone in the AM260W reaction centre suggests that this long-lived radical pair state is P(+)Q(B)(-), although the exact reduction/protonation state of the Q(B) quinone remains to be confirmed. The blockage of active branch (A-branch) electron transfer by the AM260W mutation implies that this P(+)Q(B)(-) state is formed by electron transfer along the so-called inactive branch (B-branch) of reaction centre cofactors. We discuss how further mutations may affect the yield of the P(+)Q(B)(-) state, including a double alanine mutation (EL212A/DL213A) that probably has a direct effect on the efficiency of the low yield electron transfer step from the anion of the B-branch bacteriopheophytin (H(B)(-)) to the Q(B) ubiquinone.

Free Radicals↗