Exciton interactions of chlorophyll tetramer in water-soluble chlorophyll-binding protein BoWSCP.

The exciton interaction of four chlorophyll a (Chl a) molecules in a symmetrical tetrameric complex of the water-soluble chlorophyll-binding protein BoWSCP was analyzed in the pH range of 3-11. Exciton splitting ΔE = 232 ± 2 cm-1 of the Qy band of Chl a into two subcomponents with relative intensities of 78.1 ± 0.7 % and 21.9 ± 0.7 % was determined by a joint decomposition of the absorption and circular dichroism spectra into Gaussian functions. The exciton coupling parameters were calculated based on the BoWSCP atomic structure in three approximations: the point dipole model, the distributed atomic monopoles, and direct ab initio calculations in the TDDFT/PCM approximation. The Coulomb interactions of monomers were calculated within the continuum model using three values of optical permittivity. The models based on the properties of free Chl a in solution suffer from significant errors both in estimating the absolute value of the exciton interaction and in the relative intensity of exciton transitions. Calculations within the TDDFT/PCM approximation reproduce the experimentally determined parameters of the exciton splitting and the relative intensities of the exciton bands. The following factors of pigment-protein and pigment-pigment interactions were examined: deviation of the macrocycle geometry from the planar conformation of free Chl; the formation of hydrogen bonds between the macrocycle and water molecules; the overlap of wave functions of monomers at close distances. The most significant factor is the geometrical deformation of the porphyrin macrocycle, which leads to an increase in the dipole moment of Chl monomer from 5.5 to 6.9 D and to a rotation of the dipole moment by 15° towards the cyclopentane ring. The contributions of resonant charge-transfer states to the wave functions of the Chl dimer were determined and the transition dipole moments of the symmetric and antisymmetric charge-transfer states were estimated.

The Use of Microencapsulated Autologous Thrombi for Modelling Chronic Thromboembolic Pulmonary Hypertension in Rats.

Here we developed a model of chronic thromboembolic pulmonary hypertension (CTEPH) using repeated intravenous administration of microencapsulated thrombi with a controlled rate of biodegradation. Autologous thrombi encapsulated in alginate microspheres with a diameter of 190±48 µm were intravenously injected to rats 8 times every 4 days. In the comparison group, nonmodified thrombi were injected. After 6 weeks, a significant increase in systolic pressure in the right ventricle, a decrease in exercise tolerance, and an increase in the index of vascular wall hypertrophy were revealed in the group receiving injections of microencapsulated thrombi in comparison with the group receiving nonmodified thrombi and healthy animals. Thus, the developed representative CTEPH model can be used to test promising pharmacological substances.

Pararenal Fat and Renal Dysfunction in Patients without Significant Cardiovascular Disease.

INTRODUCTION: Accumulation of fat tissue around the kidneys is considered to be a risk factor for chronic kidney disease (CKD). The objective of the study was to investigate the association of pararenal fat tissue (PRFT) and renal dysfunction in patients without clinically significant cardiovascular diseases (CVDs). METHODS: The study included 320 patients without CVDs (mean age 63.8 ± 13.9 years). All patients underwent anthropometric measurements, standard biochemical blood tests, including a lipid panel and uric acid concentration. Glomerular filtration rate (GFR) was calculated using the CKD-EPI formula. All patients underwent computed tomography of the abdomen with measurement of the PRFT thickness. The research results were processed using StatSoftStatistica 10.0 software. RESULTS: The average PRFT thickness was 1.45 cm [0.9; 2.0]. It was significantly higher in obese individuals when compared with patients with normal body weight (1.9 cm [1.3; 2.6] vs. 1.0 cm [0.6; 1.7]) and overweight people (1.9 cm [1.3; 2.6] vs. 1.1 cm [0.8; 1.6]) (p < 0.001). GFR was significantly higher in subjects with normal body weight when compared with obese patients (72 mL/min/1.73 m2 [59; 83] vs. 61 mL/min/1.73 m2 [51; 70]) and overweight patients (72 mL/min/1.73 m2 [59; 83] vs. 61 mL/min/1.73 m2 [54; 72]) (p < 0.001). PRFT thickness was significantly higher in patients with stage 3 CKD when compared with those with stage 1 CKD (2.2 cm [1.6; 3.3] vs. 0.9 cm [0.9; 1.0]) and with stage 2 CKD (2.2 cm [1.6; 3.3] vs. 1.3 cm [0.9; 1.8]) (p < 0.001). A significant correlation was found between PRFT thickness and body mass index (r = 0.49, p < 0.05), waist circumference (r = 0.55, p < 0.05), GFR (r = -0.47, p < 0.05), and uric acid level (r = 0.46, p < 0.05). Multiple linear regression analysis revealed a significant relationship between GFR and age (ß ± SE -0.43 ± 0.15, p = 0.01), PRFT thickness (ß ± SE -0.38 ± 0.14, p = 0.01) and with the level of low-density lipoprotein cholesterol (ß ± SE -0.32 ± 0.12, p = 0.01). Logistic regression analysis showed that the risk of renal dysfunction development was associated with PRFT thickness (OR = 6.198; 95% CI: 1.958-19.617; p < 0.05). ROC analysis determined the threshold values of PRFT thickness (>1.68 cm, AUC = 0.875), above which the development of renal dysfunction can be predicted (sensitivity 63.2%, specificity 93.4%). CONCLUSION: The results of our study indicate the relationship between PRFT and visceral obesity and renal dysfunction in patients without clinically significant CVDs.

Expansion of the "Sodium World" through Evolutionary Time and Taxonomic Space.

In 1986, Vladimir Skulachev and his colleagues coined the term "Sodium World" for the group of diverse organisms with sodium (Na)-based bioenergetics. Albeit only few such organisms had been discovered by that time, the authors insightfully noted that "the great taxonomic variety of organisms employing the Na-cycle points to the ubiquitous distribution of this novel type of membrane-linked energy transductions". Here we used tools of bioinformatics to follow expansion of the Sodium World through the evolutionary time and taxonomic space. We searched for those membrane protein families in prokaryotic genomes that correlate with the use of the Na-potential for ATP synthesis by different organisms. In addition to the known Na-translocators, we found a plethora of uncharacterized protein families; most of them show no homology with studied proteins. In addition, we traced the presence of Na-based energetics in many novel archaeal and bacterial clades, which were recently identified by metagenomic techniques. The data obtained support the view that the Na-based energetics preceded the proton-dependent energetics in evolution and prevailed during the first two billion years of the Earth history before the oxygenation of atmosphere. Hence, the full capacity of Na-based energetics in prokaryotes remains largely unexplored. The Sodium World expanded owing to the acquisition of new functions by Na-translocating systems. Specifically, most classes of G-protein-coupled receptors (GPCRs), which are targeted by almost half of the known drugs, appear to evolve from the Na-translocating microbial rhodopsins. Thereby the GPCRs of class A, with 700 representatives in human genome, retained the Na-binding site in the center of the transmembrane heptahelical bundle together with the capacity of Na-translocation. Mathematical modeling showed that the class A GPCRs could use the energy of transmembrane Na-potential for increasing both their sensitivity and selectivity. Thus, GPCRs, the largest protein family coded by human genome, stem from the Sodium World, which encourages exploration of other Na-dependent enzymes of eukaryotes.

Electron Transfer through the Acceptor Side of Photosystem I: Interaction with Exogenous Acceptors and Molecular Oxygen.

This review considers the state-of-the-art on mechanisms and alternative pathways of electron transfer in photosynthetic electron transport chains of chloroplasts and cyanobacteria. The mechanisms of electron transport control between photosystems (PS) I and II and the Calvin-Benson cycle are considered. The redistribution of electron fluxes between the noncyclic, cyclic, and pseudocyclic pathways plays an important role in the regulation of photosynthesis. Mathematical modeling of light-induced electron transport processes is considered. Particular attention is given to the electron transfer reactions on the acceptor side of PS I and to interactions of PS I with exogenous acceptors, including molecular oxygen. A kinetic model of PS I and its interaction with exogenous electron acceptors has been developed. This model is based on experimental kinetics of charge recombination in isolated PS I. Kinetic and thermodynamic parameters of the electron transfer reactions in PS I are scrutinized. The free energies of electron transfer between quinone acceptors A1A/A1B in the symmetric redox cofactor branches of PS I and iron-sulfur clusters FX, FA, and FB have been estimated. The second-order rate constants of electron transfer from PS I to external acceptors have been determined. The data suggest that byproduct formation of superoxide radical in PS I due to the reduction of molecular oxygen in the A1 site (Mehler reaction) can exceed 0.3% of the total electron flux in PS I.

Burden of skeletal-related events in prostate cancer: unmet need in pain improvement.

PURPOSE: Up to 75% of patients with prostate cancer experience metastatic bone disease, which leads to an increased risk for skeletal-related events (SREs) including pathological bone fracture, spinal cord compression, and hypercalcemia of malignancy. Our objective was to systematically review the literature on the impact of SREs on quality of life (QOL), morbidity, and survival with a primary focus on the impact of SREs on pain in prostate cancer patients. METHODS: We searched PubMed, limiting to peer-reviewed English-language human studies published in 2000-2010. The search was based on the US Food and Drug Administration and European Medicines Agency definition of an SRE, which includes pathologic fracture, spinal cord compression (SCC), hypercalcemia of malignancy, and radiotherapy or surgery to bone resulting from severe bone pain. RESULTS: A total of 209 articles were screened, of which 173 were excluded, and 36 were included in this review. Patients with SREs had more pain and worse survival compared with no SREs. Pathologic bone fractures worsened QOL and were associated with shorter survival. Radiation therapy of SCC alleviated pain and improved morbidity. SCC was associated with decreases in patient survival. Radiation therapy and surgery to bone improved pain. CONCLUSIONS: Specific SREs are associated with worse outcomes, including increased pain, poorer QOL, morbidity, and survival. Treatment of SREs is associated with improved pain, although there remains a need for more effective treatment of SREs in prostate cancer patients.

Prevention of peroxidation of cardiolipin liposomes by quinol-based antioxidants.

In mammalian mitochondria, cardiolipin molecules are the primary targets of oxidation by reactive oxygen species. The interaction of oxidized cardiolipin molecules with the constituents of the apoptotic cascade may lead to cell death. In the present study, we compared the effects of quinol-containing synthetic and natural amphiphilic antioxidants on cardiolipin peroxidation in a model system (liposomes of bovine cardiolipin). We found that both natural ubiquinol and synthetic antioxidants, even being introduced in micro- and submicromolar concentrations, fully protected the liposomal cardiolipin from peroxidation. The duration of their action, however, varied; it increased with the presence of either methoxy groups of ubiquinol or additional reduced redox groups (in the cases of rhodamine and berberine derivates). The concentration of ubiquinol in the mitochondrial membrane substantially exceeds the concentrations of antioxidants we used and would seem to fully prevent peroxidation of membrane cardiolipin. In fact, this does not happen: cardiolipin in mitochondria is oxidized, and this process can be blocked by amphiphilic cationic antioxidants (Y. N. Antonenko et al. (2008) Biochemistry (Moscow), 73, 1273-1287). We suppose that a fraction of mitochondrial cardiolipin could not be protected by natural ubiquinol; in vivo, peroxidation most likely threatens those cardiolipin molecules that, being bound within complexes of membrane proteins, are inaccessible to the bulky hydrophobic ubiquinol molecules diffusing in the lipid bilayer of the inner mitochondrial membrane. The ability to protect these occluded cardiolipin molecules from peroxidation may explain the beneficial therapeutic action of cationic antioxidants, which accumulate electrophoretically within mitochondria under the action of membrane potential.

Mechanism of primary and secondary ion-radical pair formation in photosystem I complexes.

The mechanisms of the ultrafast charge separation in reaction centers of photosystem I (PS I) complexes are discussed. A kinetic model of the primary reactions in PS I complexes is presented. The model takes into account previously calculated values of redox potentials of cofactors, reorganization energies of the primary P700(+)A0(-) and secondary P700(+)A1(-) ion-radical pairs formation, and the possibility of electron transfer via both symmetric branches A and B of redox-cofactors. The model assumes that the primary electron acceptor A0 in PS I is represented by a dimer of chlorophyll molecules Chl2A/Chl3A and Chl2B/Chl3B in branches A and B of the cofactors. The characteristic times of formation of P700(+)A0(-) and P700(+)A1(-) calculated on the basis of the model are close to the experimental values obtained by pump-probe femtosecond absorption spectroscopy. It is demonstrated that a small difference in the values of redox potentials between the primary electron acceptors A0A and A0B in branches A and B leads to asymmetry of the electron transfer in a ratio of 70 : 30 in favor of branch A. The secondary charge separation is thermodynamically irreversible in the submicrosecond range and is accompanied by additional increase in asymmetry between the branches of cofactors of PS I.

Treatments, complications, and healthcare utilization associated with acromegaly: a study in two large United States databases.

The economic burden of acromegaly in the US has been largely unknown. We describe the prevalence of treatment patterns, complication rates, and associated healthcare utilization and costs of acromegaly in the US. Patients were identified between 1/1/2002 and 12/31/2009 in claims databases. During 1-year after each continuously-enrolled patient's first acromegaly claim, pharmacy and medical claims were used to estimate outcomes. Regression models were used to adjust outcomes. There were 2,171 acromegaly patients (mean age: 45.3 years; 49.7% female); 77.8% received the majority of their care from non-endocrinologists. Pharmacologic treatment was used by 30.8% of patients: octreotide-LAR in 18.6%, dopamine agonists in 9.8%, short-acting octreotide in 4.7%, pegvisomant in 4.1%, and lanreotide in 1.2%; 56% had biochemical monitoring. Comorbidities were common, ranging from 6.6% (colon neoplasms) to 25.6% (musculoskeletal abnormalities). Mean healthcare costs were $24,900. Adjusted analyses indicated comorbidities increased the odds of hospitalization: by 76% for musculoskeletal abnormalities; 193% for cardiovascular abnormalities; and 56% for sleep apnea (p < 0.05). Odds of emergency department visits increased by 87% (musculoskeletal) and 132% (cardiovascular abnormalities) (p < 0.01). After adjustments, colon neoplasms were associated with $8,401 mean increase in costs; musculoskeletal abnormalities with $7,502, cardiovascular abnormalities with $13,331, sleep apnea with $10,453, and hypopituitarism with $6,742 (p < 0.01). Complications are common and increase utilization and cost in acromegaly patients. Cardiovascular complications nearly tripled the odds of hospitalization (OR 2.93) and increased annual mean cost by $13,331. Adequate management of this disease may be able to reduce health care utilization and cost associated with these complications and with acromegaly in general.

Interaction of tetraphenylphosphonium and dodecyltriphenylphosphonium with lipid membranes and mitochondria.

The permeability of a planar lipid membrane (composed of diphytanoylphosphatidylcholine) for tetraphenylphosphonium (TPP) was investigated. The observed level of the diffusion potential generated as a function of the TPP concentration gradient differed from the theoretically expected value, possibly due to proton leakage of the membrane mediated by the traces of fatty acids in the phospholipid forming the membrane. Using the molecular dynamics approach to study movement of TPP and dodecyltriphenylphosphonium (C(12)TPP) with different affinity to the lipid bilayer through a bilayer lipid membrane, it was found that C(12)TPP has a greater affinity to the membrane surface than TPP. However, the two cations have the same activation energy for transmembrane transfer. Interaction of TPP and C(12)TPP with tightly-coupled mitochondria from the yeast Yarrowia lipolytica was also investigated. At low, micromolar concentrations, both cations are "relatively weak, mild uncouplers", do not shunt electron transfer along the respiratory chain, do not disturb (damage) the inner mitochondrial membrane, and profoundly promote the uncoupling effect of fatty acids. At higher concentrations they inhibit respiration in state 3, and at much higher concentrations they induce swelling of mitochondria, possibly due to their detergent action.

Mitochondrial-targeted plastoquinone derivatives. Effect on senescence and acute age-related pathologies.

Plastoquinone, a very effective electron carrier and antioxidant of chloroplasts, was conjugated with decyltriphenylphosphonium to obtain a cation easily penetrating through membranes. This cation, called SkQ1, is specifically targeted to mitochondria by electrophoresis in the electric field formed by the mitochondrial respiratory chain. The respiratory chain also regenerates reduced SkQ1H(2) from its oxidized form that appears as a result of the antioxidant activity of SkQ1H(2). SkQ1H(2) prevents oxidation of cardiolipin, a mitochondrial phospholipid that is especially sensitive to attack by reactive oxygen species (ROS). In cell cultures, SkQ1 and its analog plastoquinonyl decylrhodamine 19 (SkQR1) arrest H(2)O(2)-induced apoptosis. When tested in vivo, SkQs (i) prolong the lifespan of fungi, crustaceans, insects, fish, and mice, (ii) suppress appearance of a large number of traits typical for age-related senescence (cataract, retinopathies, achromotrichia, osteoporosis, lordokyphosis, decline of the immune system, myeloid shift of blood cells, activation of apoptosis, induction of ß-galactosidase, phosphorylation of H2AX histones, etc.) and (iii) lower tissue damage and save the lives of young animals after treatments resulting in kidney ischemia, rhabdomyolysis, heart attack, arrhythmia, and stroke. We suggest that the SkQs reduce mitochondrial ROS and, as a consequence, inhibit mitochondria-mediated apoptosis, an obligatory step of execution of programs responsible for both senescence and fast "biochemical suicide" of an organism after a severe metabolic crisis.

[Endovideosurgical antireflux operations in combination with cholecystectomy].

In the city center of endovideosurgery during 1999-2005 there were 205 patients examined and treated for cholelithiasis combined with gastro-esophageal-reflux disease (GERD) and hiatal hernias. Simultaneous interventions, antireflux operation and cholecystectomy were performed in 150 patients. Cholecystectomy followed by conservative treatment of GERD was performed in 55 patients. The results of treatment were followed up during 1 and 6 months.

Ubiquinone reduction in the photosynthetic reaction centre of Rhodobacter sphaeroides: interplay between electron transfer, proton binding and flips of the quinone ring.

This review is focused on reactions that gate (control) the electron transfer between the primary quinone Q(A) and secondary quinone Q(B) in the photosynthetic reaction centre of Rhodobacter sphaeroides. The results on electron and proton transfer are discussed in relation to structural information and to the steered molecular dynamics simulations of the Q(B) ring flip in its binding pocket. Depending on the initial position of Q(B) in the pocket and on certain conditions, the rate of electron transfer is suggested to be limited either by the quinone ring flip or by the charge-compensating proton equilibration between the surface and the buried Q(B) site.

Proton transfer dynamics at membrane/water interface and mechanism of biological energy conversion.

Proton transfer between water and the interior of membrane proteins plays a key role in bioenergetics. Here we survey the mechanism of this transfer as inferred from experiments with flash-triggered enzymes capturing or ejecting protons at the membrane surface. These experiments have revealed that proton exchange between the membrane surface and the bulk water phase proceeds at > or =1 msec because of a kinetic barrier for electrically charged species. From the data analysis, the barrier height for protons could be estimated as about 0.12 eV, i.e., high enough to account for the observed retardation in proton exchange. Due to this retardation, the proton activity at the membrane surface might deviate, under steady turnover of proton pumps, from that measured in the adjoining water phase, so that the driving force for ATP synthesis might be higher than inferred from the bulk-to-bulk measurements. This is particularly relevant for alkaliphilic bacteria. The proton diffusion along the membrane surface, on the other hand, is unconstrained and fast, occurring between the neighboring enzymes at less than 1 microsec. The anisotropy of proton dynamics at the membrane surface helps prokaryotes diminish the "futile" escape of pumped protons into the external volume. In some bacteria, the inner membrane is invaginated, so that the "ejected" protons get trapped in the closed space of such intracellular membrane "sacks" which can be round or flat. The chloroplast thylakoids and the mitochondrial cristae have their origin in these intracellular structures.

[Modified laparoscopic fundoplication in the treatment of gastroesophageal reflux]. / Modifitsirovannaia laparoskopicheskaia fundoplikatsiia v lechenii gastroézofageal'noi refliuksnoi bolezni.

The results of laparoscopic fundoplication in patients with the gastroesophageal reflux disease are described. Operations were performed by the classical Dor method (19 patients) and by a modified method (35 patients). An analysis of results of the operation has shown effectiveness and safety of using the modified method of laparoscopic fundoplication.

Inter-subunit rotation and elastic power transmission in F0F1-ATPase.

ATP synthase (F-ATPase) produces ATP at the expense of ion-motive force or vice versa. It is composed from two motor/generators, the ATPase (F1) and the ion translocator (F0), which both are rotary steppers. They are mechanically coupled by 360 degrees rotary motion of subunits against each other. The rotor, subunits gamma(epsilon)C10-14, moves against the stator, (alphabeta)3delta(ab2). The enzyme copes with symmetry mismatch (C3 versus C10-14) between its two motors, and it operates robustly in chimeric constructs or with drastically modified subunits. We scrutinized whether an elastic power transmission accounts for these properties. We used the curvature of fluorescent actin filaments, attached to the rotating c ring, as a spring balance (flexural rigidity of 8.10(-26) N x m2) to gauge the angular profile of the output torque at F0 during ATP hydrolysis by F1. The large average output torque (56 pN nm) proved the absence of any slip. Angular variations of the torque were small, so that the output free energy of the loaded enzyme decayed almost linearly over the angular reaction coordinate. Considering the three-fold stepping and high activation barrier (>40 kJ/mol) of the driving motor (F1) itself, the rather constant output torque seen by F0 implied a soft elastic power transmission between F1 and F0. It is considered as essential, not only for the robust operation of this ubiquitous enzyme under symmetry mismatch, but also for a high turnover rate under load of the two counteracting and stepping motors/generators.

F-ATPase: forced full rotation of the rotor despite covalent cross-link with the stator.

In ATP synthase (F(O)F(1)-ATPase) ion flow through the membrane-intrinsic portion, F(O), drives the central "rotor", subunits c(10)epsilongamma, relative to the "stator" ab(2)delta(alphabeta)(3). This converts ADP and P(i) into ATP. Vice versa, ATP hydrolysis drives the rotation backwards. Covalent cross-links between rotor and stator subunits have been shown to inhibit these activities. Aiming at the rotary compliance of subunit gamma we introduced disulfide bridges between gamma (rotor) and alpha or beta (stator). We engineered cysteine residues into positions located roughly at the "top," "center," and "bottom" parts of the coiled-coil portion of gamma and suitable residues on alpha or beta. This part of gamma is located at the center of the (alphabeta)(3) domain with its C-terminal part at the top of F(1) and the bottom part close to the F(O) complex. Disulfide bridge formation under oxidizing conditions was quantitative as shown by SDS-polyacrylamide gel electrophoresis and immunoblotting. As expected both the ATPase activities and the yield of rotating subunits gamma dropped to zero when the cross-link was formed at the center (gammaL262C <--> alphaA334C) and bottom (gammaCys(87) <--> betaD380C) positions. But much to our surprise disulfide bridging impaired neither ATP hydrolysis activity nor the full rotation of gamma and the enzyme-generated torque of oxidized F(1), which had been engineered at the top position (gammaA285C <--> alphaP280C). Apparently the high torque of this rotary engine uncoiled the alpha-helix and forced amino acids at the C-terminal portion of gamma into full rotation around their dihedral (Ramachandran) angles. This conclusion was supported by molecular dynamics simulations: If gammaCys(285)-Val(286) are attached covalently to (alphabeta)(3) and gammaAla(1)-Ser(281) is forced to rotate, gammaGly(282)-Ala(284) can serve as cardan shaft.

Viscoelastic dynamics of actin filaments coupled to rotary F-ATPase: angular torque profile of the enzyme.

ATP synthase (F(O)F(1)) operates as two rotary motor/generators coupled by a common shaft. Both portions, F(1) and F(O), are rotary steppers. Their symmetries are mismatched (C(3) versus C(10-14)). We used the curvature of fluorescent actin filaments, attached to the rotating c-ring, as a spring balance (flexural rigidity of 8. 10(-26) Nm(2)) to gauge the angular profile of the output torque at F(O) during ATP hydrolysis by F(1) (see theoretical companion article (. Biophys. J. 81:1234-1244.)). The large average output torque (50 +/- 6 pN. nm) proved the absence of any slip. Variations of the torque were small, and the output free energy of the loaded enzyme decayed almost linearly over the angular reaction coordinate. Considering the threefold stepping and high activation barrier of the driving motor proper, the rather constant output torque implied a soft elastic power transmission between F(1) and F(O). It is considered as essential, not only for the robust operation of this ubiquitous enzyme under symmetry mismatch, but also for a high turnover rate of the two counteracting and stepping motor/generators.

Viscoelastic dynamics of actin filaments coupled to rotary F-ATPase: curvature as an indicator of the torque.

ATP synthase (F-ATPase) operates as an electrochemical-to-mechanical-to-chemical energy transducer with an astounding 360 degrees rotary motion of subunits epsilongammac(10-14) (rotor) against delta(alphabeta)(3)ab(2) (stator). The enzyme's torque as a function of the angular reaction coordinate in relation to ATP-synthesis/hydrolysis, internal elasticity, and external load has remained an important issue. Fluorescent actin filaments of micrometer length have been used to detect the rotation as driven by ATP hydrolysis. We evaluated the viscoelastic dynamics of actin filaments under the influence of enzyme-generated torque, stochastic Langevin force, and viscous drag. Modeling with realistic parameters revealed the dominance of the lowest normal mode. Because of its slow relaxation (approximately 100 ms), power strokes of the enzyme were expected to appear strongly damped in recordings of the angular velocity of the filament. This article describes the theoretical background for the alternative use of the filament as a spring balance. The enzyme's angular torque profile under load can be gauged by measuring the average curvature and the stochastic fluctuations of actin filaments. Pertinent experiments were analyzed in the companion paper.

Proton transfer in Azotobacter vinelandii ferredoxin I: entatic Lys84 operates as elastic counterbalance for the proton-carrying Asp15.

In ferredoxin I from Azotobacter vinelandii, the reduction of a [3Fe-4S] iron-sulphur cluster is coupled with the protonation of the mu2S sulphur atom that is approx. 6 A away from the protein boundary. The recent study of the site-specific mutants of ferredoxin I led to the conclusion that a particular surface aspartic residue (Asp15) is solely responsible for the proton transfer to the mu2S atom by 'rapid penetrative excursions' (K. Chen, J. Hirst, R. Camba, C.A. Bonagura, C.D. Stout, B.K. Burgess, F.A. Armstrong, Nature 405 (2000) 814-817). In the same paper it has been reported that the replacement of Asp15 by glutamate led to the blockage of the enzyme, although glutamate, with its longer and more flexible side chain, should apparently do even better as a mobile proton carrier than aspartate. We tackled this puzzling incompetence of Glu15 by molecular dynamics simulations. It was revealed that the conformational alterations of Asp15 are energetically balanced by the straining of the nearby Lys84 side chain in wild-type ferredoxin I but not in the Asp15-->Glu mutant. Lys84 in ferredoxin I of A. vinelandii seems to represent the first case where the strained (entatic) conformation of a particular amino acid side chain could be directly identified in the ground state of an enzyme and assigned to a distinct mechanism of energy balance during the catalytic transition.