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At least 19 recordsLinked to original sources
PubMed1978

Magnetic coupling of the molybdenum and iron-sulphur centres in xanthine oxidase and xanthine dehydrogenases.

Magnetic interaction between molybdenum and one of the iron-sulphur centres in milk xanthine oxidase [Lowe, Lynden-Bell & Bray (1972) Biochem. J. 130, 239-249] was studied further, with particular reference to the newly discovered Mo(V) e.p.r.(electron-paramagnetic-resonance) signal, Resting II [Lowe, Barber, Pawlik & Bray (1976) Biochem. J. 155, 81-85]. E.p.r. measurements at 35GHz near to 4.2K showed that the interaction has the same sign at all molybdenum orientations and is ferromagnetic. The predicted splitting of the e.p.r. signal from the reduced iron-sulphur centre, Fe/S I, was observed, Providing positive identification of this as the other interacting species. Chemical modification of the molybdenum environment in xanthine oxidase can change the size of the interaction severalfold, but interaction always remains approximately isotropic. The interaction in turkey liver xanthine dehydrogenase is indistinguishable from that in the oxidase. However, a bacterial xanthine dehydrogenase with different iron-sulphur centres shows rather larger interaction. Guanidinium chloride disturbs the iron-sulphur centres of the oxidase, and when this occurs there is a parallel and relatively small change in the interaction. Removal of flavin from the molecule, or raising the pH to 12.0, changes the interaction slightly without affecting the chromophores themselves. It is concluded that the Fe/S I centre and the Mo are at least 1.0nm and probably nearer 2.5nm apart, and that the conformation of the protein between them is relatively stable up to pH 12.

Animals↗
PubMed1976

Cobalt bovine superoxide dismutase. Reactivity of the cobalt chromophore in the copper-containing and in the copper-free enzyme.

1. The reactivity of the zinc site of bovine superoxide dismutase has been probed by observing optical and electron paramagnetic resonance changes, under several conditions, of the Co(II)-substituted protein. 2. Only in the absence of copper are the optical and electron paramagnetic resonance spectra of the cobalt chromophore appreciably affected by alkaline pH or by cyanide. With both reagents the reaction with the copper-containing protein appears to involve the water molecule bound to the copper and does not affect the magnetic coupling between copper and cobalt. 3. The reaction of cyanide with the copper-free Co(II) protein leads to a slow detachment of cobalt from the protein as pentacyanocobalt. An oxygen adduct forms in air, analogous to that described in Co(II) carbonic anhydrase (Haffner, P. H. and Coleman, J. E. (1975) J. Biol. Chem. 250, 996--1005.) 4. Acid titration modifies the Co(II) spectra in the same way in the Cu-containing and in the Cu-free protein and brings about uncoupling of the Co(II)--Cu(II) system. Protonation of histidine-61 on the zinc facing nitrogen is suggested. 5. H2O2 modifies the cobalt chromophore only in the presence of copper. Magnetic coupling between Cu(II) and Co(II) seems to be still present after H2O2 inactivation of the enzyme.

Animals↗
PubMed1975

Evaluation of a magnetic bladder pump for neurogenic bladders.

A new bladder pump prosthesis has been designed and evaluated in the normal dog bladder. This encompasses a magnetic pump located subcutaneously with internal silicone catheters from bladder to the urethra. The pump is powered from a hand-held activator which is magnetically coupled externally across the skin. This pump was evaluated in 12 dogs for an average of 65 days and provided adequate emptying of the bladder without alteration of the normal urinary tract or pump malfunction. The potential and limitations of this new approach are discussed.

Animals↗
PubMed1976

DNA-histones, a computer model.

The model of DNA-histones has the following elements: 1. The hydrogen bonds between the complementary nucleotide bases function as informational gates. When the electrons pi of one nucleotide base are excited, an exchange of protons is produced between the two complementary bases. The result is the displacement of the conjugated double bonds which facilitates the inter-molecular transmission of the electronic wave of excitation by electro-magnetic coupling. 2. Each triplet of nucleotide bases of DNA fixes one definite amino acid (as in the genetic code). Between the nucleotide bases and the amino acids there are constituted informational gates, which ensure the circulation of the electronic wave of excitation. 3. An input signal molecule arrives at the receiver gene and unleashes the activity of the enzymes which introduce in the DNA-histones system the electronic wave of excitation. The electronic wave of excitation arises as a result of the break of the high-energy bonds of ATP. Then, the electronic excitation is transmitted to the productor gene where it represents the signal for starting the synthesis of the mRNA.

Adenosine Triphosphate↗
PubMed1975

Primary acceptor in bacterial photosynthesis: obligatory role of ubiquinone in photoactive reaction centers of Rhodopseudomonas spheroides.

Reaction centers were found to bind two ubiquinones, both of which could be removed by o-phenanthroline and the detergent lauryldimethylamine oxide. One ubiquinone was more easily removed than the other. The low-temperature light-induced optical and electron paramagnetic resonance (EPR) changes were eliminated and restored upon removal and readdition of ubiquinone and were quantitatively correlated with the amount of tightly bound ubiquinone. We, therefore, conclude that this ubiquinone plays an obligatory role in the primary photochemistry. The easily removed ubiquinone is thought to be the secondary electron acceptor. The low-temperature charge recombination kinetics, as well as the optical and EPR spectra, were the same for untreated reaction centers and for those reconstituted with ubiquinone. This indicates that extraction and reconstitution were accomplished without altering the conformation of the active site. Reaction centers reconstituted with other quinones also showed restored photochemical activity, although they exhibited changes in their low-temperature recombination kinetics and light-induced (g = 1.8) EPR signal is interpreted in terms of a magnetically coupled ubiquinone--Fe2+ acceptor complex. A possible role of iron is to facilitate electron transfer between the primary and secondary ubiquinones.

Kinetics↗
PubMed1978

Development of compact thermal and electrical energy converters left heart assist systems.

The thermal converter for left heart assist systems consists of an engine which converts thermal energy to a flow of pressurized helium and a helium powered actuator/controller which powers and controls a PVAD pusher plate blood pump. The 0.43 L, 0.94 kg engine requires 20 watts of thermal input. In vitro and in vivo testing have demonstrated that the system synchronizes and provides left ventricle relief from 60 to 150 beats/min. The concepts potential for long life is based on: the inert environment for all internal components; the hermetic sealing capability resulting from a linear magnetic coupling blood pump drive; fluid control; and titanium external metal surfaces. Endurance testing has demonstrated that the converter shows promise of providing a high reliability 10 yr life. Many wear and fatigue sensitive components have demonstrated the 10 yr capability during accelerated life testing.

Animals↗
PubMed2025

Personalized Repetitive Transcranial Magnetic Stimulation (PrTMS®) Coupled with Transcranial Photobiomodulation (tPBM) For Co-Occurring Traumatic Brain Injury (TBI) and Post-Traumatic Stress Disorder (PTSD).

This study provides further evidence demonstrating the beneficial effects of PrTMS® treatment in co-occurring disorders. Furthermore, this study illustrates the benefit of augmenting PrTMS® with tPBM for superior outcomes. The positive results of this novel case study can be attributed to brain wave neuromodulation and increased neuronal ATP production, resulting in synergistic enhanced neuroplasticity and brain optimization. Further, large-scale, randomized and blinded studies are recommended to validate our promising preliminary observations utilizing multifaceted interventions for co-occurring disorders.

Co-Occurring Disorders↗
PubMed1979

Mechanism of Lactobacillus leichmannii ribonucleotide reductase studied with Coalpha-[alpha-(Aden-9-yl)]-Cobeta-adenosylcobamide (Pseudocoenzyme B12) as coenzyme.

Coalpha-[alpha-(Aden-9-yl)]-Cobeta-adenosylcobamide (pseudocoenzyme B12) purified from Clostridium tetanomorphum has been reacted with ribonucleotide reductase purified from Lactobacillus leichmannii under various conditions, and the properties of the products obtained have been compared by electron paramagnetic resonance (EPR) with those previously reported for products formed from the normal coenzyme (adenosylcobalamin). The rapidly formed intermediate and the slowly formed "doublet" species from the pseudocoenzyme have EPR spectra identical with those formed from the normal coenzyme. This and other considerations make it less likely that the unusual magnetic properties of the rapidly formed intermediate are due to strongly distorted octahedral symmetry about Co(II) as previously postulated. Instead it is probable that the EPR spectrum is due to interaction of the radical pair by both exchange coupling and magnetic dipole--dipole coupling. Although Coalpha-[alpha-(aden-9-YL)]cob(II)amide in solution does not show superhyperfine splitting in the EPR spectrum because of its base-off configuration, the cob(II)amide formed by degradation of the pseudocoenzyme within the catalytic site of the enzyme did show triplets due to a nitrogen axially coordinated to cobalt. This suggests that binding of the cob(II)amide to the reductase catalytic site causes a shift to the base-on form.

Electron Spin Resonance Spectroscopy↗
PubMed2026

Glymphatic dysfunction mediates inflammation-driven vascular burden and cognitive decline in cerebral small vessel disease.

BACKGROUND: Cerebral small vessel disease (CSVD) is increasingly recognized as a disorder involving microvascular dysfunction, impaired perivascular clearance, and inflammatory processes. However, how systemic inflammatory burden, neurovascular coupling (NVC), glymphatic MRI markers, vascular lesion burden, and cognition are interrelated remains unclear. MATERIALS AND METHODS: In this prospective study, 155 patients with CSVD and 70 healthy controls (HCs) underwent multimodal MRI. NVC was quantified using the cerebral blood flow/fractional amplitude of low-frequency fluctuations ratio. Glymphatic function was assessed via the diffusion tensor image analysis along the perivascular space (ALPS) index, choroid plexus volume (CPV), and perivascular space (PVS) fractions. Structural equation modeling (SEM) was employed to evaluate the direct and indirect effects of inflammatory markers on vascular burden and cognitive performance. RESULTS: Patients with CSVD exhibited significantly diminished NVC (specifically in the right median cingulate and left frontal gyri) and impaired glymphatic function (lower ALPS-index; higher CPV and PVS fractions) compared to HCs. SEM revealed that inflammatory biomarkers exerted both a direct effect on vascular burden and a substantial indirect effect (accounting for 66.3% of the total effect) mediated through two pathways: a single-mediation path via glymphatic function (42.8%) and a serial-mediation path via NVC and glymphatic function (23.5%). Increased vascular burden was significantly associated with poorer cognitive performance. CONCLUSION: Inflammation drives CSVD progression and cognitive decline primarily through the disruption of NVC and glymphatic clearance mechanisms. These findings highlight glymphatic dysfunction as a critical mediator of inflammation-related structural brain damage.

Humans↗
PubMed2025

TMS-EEG in postictal psychosis of epilepsy.

BACKGROUND: Postictal psychosis (PIP) is a poorly understood complication affecting 2 % of individuals with epilepsy. Genomic and neuroimaging studies suggest parallels with schizophrenia. OBJECTIVES: To determine whether Transcranial Magnetic Stimulation coupled with Electroencephalography (TMS-EEG), can reveal schizophrenia-like changes in PIP, especially in Natural Frequency (NF), gamma band Event-Related Spectral Perturbation (ERSP), the N100 peak, and global mean field power (GMFP). METHODS: We applied TMS-EEG targeting the non-dominant hemisphere premotor area in people with focal epilepsy (PWE) with a history of PIP (n = 7) and PWE without any history of psychosis (n = 14). Two-tailed t-tests were applied to TMS-EEG metrics previously studied in schizophrenia to look for differences between the groups, with subgroup analyses excluding participants using benzodiazepines. RESULTS: Demographic and clinical characteristics were similar across the two groups. No significant differences were seen in NF (p = 0.98). We observed a delayed N100 peak latency in the PIP group when excluding those with regular benzodiazepine use (p = 0.05) and increased global mean field power during the 400-600 ms phase of the TEP (p = 0.02). Mean ERSP within the gamma band was lower in the PIP group, though this did not reach statistical significance (p = 0.08). CONCLUSION: This is the first study to apply TMS-EEG in individuals with PIP, demonstrating feasibility and providing methodological insights for future studies. Preliminary findings, including increased GMFP and delayed N100 latency in PIP, suggest possible disruptions in cortical excitability similar to schizophrenia, warranting further investigation.

Humans↗
PubMed2026

Low-Carbon-Residue Multi-Principal-Element Magnetic Alloys for Excellent Microwave Absorption.

Magnetic alloy/carbon composites are promising microwave absorbers due to abundant interfaces and multiple loss mechanisms. However, reducing carbon content while maintaining uniform magnetic component distribution remains challenging. We report a spray-drying strategy to address this. By tuning nitrate precursor ratios and optimizing thermal treatment, we synthesize low-carbon alloy/oxide microspheres with uniformly distributed alloy phases. Limiting carbon content improves impedance matching, while selective nitrate precipitation creates a magnetic alloy architecture that suppresses nanoparticle agglomeration and enhances interfacial polarization. For this multiscale synergistic polarization is achieved: highly conductive Cu maximizes conduction loss, insulating Al2O3 buffers impedance, and Mn provides abundant polarization centers. The resulting microspheres exhibit tunable, exceptional performance. The attenuation-dominated FeCuMn system achieves -48.2 dB minimum reflection loss at 1.5 mm thickness. The impedance-matched FeCuAl system delivers an ultra-broad effective absorption bandwidth (EAB) of 5.12 GHz. Additionally, the FeAlMn system demonstrates superior polarization miniaturization for optimal absorption at extremely thin matching thicknesses. This work provides a practical strategy for designing electromagnetic composite structures with tunable component distribution.

customizable multicomponent↗
PubMed1979

Nitrogenase XI: Mössbauer studies on the cofactor centers of the MoFe protein from Azotobacter vinelandii OP.

We have studied the MoFe protein from Azotobacter vinelandii OP with Mössbauer spectroscopy in applied magnetic fields up to 50 kG. The results are as follows. (1) The Mössbauer spectra of the S = 3/2 centers, which reside on the cofactor of nitrogenase, have been decomposed into six subcomponents. This suggests that each center contains 5-7, most probably 6, Fe atoms, thus confirming our earlier conclusions which were based on the quantitation of EPR data and on the assumption that the MoFe protein contains (30 +/- 2) Fe atoms. (2) Analysis of the high-field data shows that three subsites are characterized by a positive magnetic hyperfine coupling constant, A0, while A0 is negative for the other three sites. This observation demonstrates that the S = 3/2 centers are spin-coupled structures. (3) The zero-field splitting parameter D = +(6 +/- 1.5) cm-1 obtained from the Mössbauer data is in good agreement with our earlier EPR results, D approximately +5.5 cm-1. (4) The resolution of the Mössbauer spectra of the MoFe protein can be dramatically increased by employing Fourier transform deconvolution techniques. This allows a clear demonstration of spectral component S.

Azotobacter↗
PubMed1976

Phosphorus-31 Fourier transform nuclear magnetic resonance study of mononucleotides and dinucleotides. 2. Coupling constants.

Stereosensitive 3JPH and 4JPH phosphorus-proton coupling constants have been measured directly from the phosphorus-31 nuclear magnetic resonance (NMR) spectra of a variety of adenine, thymine, and uracil 3'-mononucleotides, 5'-mononucleotides, their cyclic analogues, and the corresponding dinucleotides, under various conditions of pH and temperature. For all 5'-mononucleotides, the identical 3JPH coupling to phosphorus of the two H5' protons is found essentially independent of the nature of the base, the presence of a 2'-OH on the sugar ring, the temperature, and the pH; the "gauche-gauche" rotamers about C5'-O5' and C4'-C5' remain overwhelmingly (85%) preferred. The "gauche" arrangement during C3'-O3' is favored in all cases for 3'-mononucleotides. However, while no sizeable pH effect is noted on 3'-monodeoxyribonucleotides, the pH dependence of 3JPH3 in 3'-monoribonucleotides strongly suggests an interaction between the 3'-phosphate and the 2'-OH. Molecular features affecting the magnitude of 4JPH coupling constants are discussed together with pH and temperature effects. The time-averaged preferential structural features of mononucleotides are found in dinucleotides with a higher probability; hence, dimerization induces an increase in the statistical conformational purity of the phosphodiester-sugar backbone, even at extreme pH. Temperature studies point out that the thermal unwinding of stacked dinucleotides occurs mainly via rotation about P3'-O3' and P5'-O5' bond axes.

Binding Sites↗
PubMed1975

The application of nuclear magnetic resonance spectroscopy to the study of natural and model membranes.

This review article outlines some potentials and limits of the recent application of high resolution Nuclear Magnetic Resonance technique--coupled to the Fourier transformation methods--to the study of biological membranes. Molecular arrangement and dynamical structure characters can be assessed at the level of individual chemical groups in lipid bilayer regions of natural and model membranes, through the determination of physical parameters like chemical shifts, spin-lattice (T1) and spin-spin (T2) nuclear magnetic relaxation times. The results of some significant experiments carried out on single-wall lecithin vesicles as well as on intact natural membranes, are summarized and discussed. Useful information can be obtained on the lipid fatty-acid chains thermal transition, by comparing two lecithin vesicles of the same size, formed by the same host lecithin, but incorporated with different molecular components. In particular, T1 and T2 measurements, interpreted in terms of a two- (or more-) correlation time theoretical models, are able to demonstrate different degrees of motional anisotropy in bilayers formed by mixed lecithins or by mixtures of lecithin and fatty acids, possessing moderately different chain lengths [13]. Chromophore-containing molecules, like chlorophyll [12] or fluorescent probes [14] can be located, within few Angstroms, in a lipid bilayer through proton chemical shift measurements; in addition the perturbation of the lipid membrane structure, as induced by the incorporated probe, is assessed mainly in terms of the intramolecular dynamical structure of the host lecithin molecules, by means of T1 and linewidth studies. The comparison of the n.m.r. relaxation behaviour in intact membranes and in vesicles formed by their extracted lipids may, finally, provide indirect information on the lipid-protein intermolecular interactions and relative mobility, besides indicating the intramolecular mobility characters of the lipid bilayer regions of the membrane.

Fatty Acids↗
PubMed1977

Enkephalin: conformational analysis by means of empirical energy calculations.

Low-energy conformations of methionine-enkephalin were generated by means of an empirical method of computation. Many compact conformations, including those containing various standard bends, were of comparable energy. However, one conformation was found to have a potential energy about 5 kcal/mol (21 X 10(3) J/mol) below that of the large group of compact conformations. In this conformation, the 3-glycyl and 4-phenylalanyl residues form a bend of type II'. The conformation is stabilized by a hydrogen bond between the OH group of the 1-tyrosine side chain and the C==O group of 3-glycine or 4-phenylalanine. The phenylalanine and methionine side chains are relatively unrestricted. The conformation is consistent with published nuclear magnetic resonance parameters--coupling constants, temperature dependence of the chemical shift, and spin-lattice relaxation times. It is likely that the molecule undergoes a conformational change when it is bound to the receptor. Leucine-enkephalin appears to have the same conformation as its methionine homolog.

Calorimetry↗
PubMed1978

A new method of chemical modification of N6-amino group in adenine nucleotides with formaldehyde and a thiol and its application to preparing immobilized ADP and ATP.

Reaction of AMP with formaldehyde and 3-mercaptopropionic acid at pH 11.7 gave a new AMP derivative, N6-[(2-carboxyethyl)thiomethyl]-AMP (I) in 91% yield and reaction at pH 3.1 gave another new derivative, N6,N6-bis[(2-carboxyethyl)thiomethyl]-AMP (II) in 57% yield. The structures were determined by their 13C and 1H nuclear magnetic resonance spectra coupled with those of the simple analogues, N6-[(2-carboxyethyl)thiomethyl]-9-methyladenine (III) and N6,N6-bis[(2-carboxyethyl)thiomethyl]-9-methyladenine (IV) which were synthesized from 9-methyladenine in the same way as for derivatives I and II. ADP and ATP were treated in the same way as AMP to afford the corresponding carboxyl derivatives, N6-[(2-carboxyethyl)thiomethyl]-ADP (V), N6-[(2-carboxyethyl)thiomethyl]-ATP (VI), N6,N6-bis[(2-carboxyethyl)thiomethyl]-ADP (X) and N6,N6-bis[(2-carboxyethyl)thiomethyl]-ATP (XI) in 71%, 75%, 53% and 40% yield, respectively. These compounds were coupled to 1,3-diaminopropane with a water-soluble carbodiimide to give the corresponding amino derivatives, N6-([N-3-aminopropyl)carbamoylethyl]thiomethyl)-ADP (VIII), N6-(N-(3-aminopropyl)carbamoylethyl]thiomethyl)-ATP (IX), N6,N6-bis([N-(3-aminopropyl)carbamoylethyl]thiomethyl)-ADP (XIII), and N6,N6-bis([N-(3-aminopropyl)carbamoylethyl]thiomethyl)-ATP (XIV), which were further bound to CNBr-activated dextran to give new polymer-bound derivatives of ADP and ATP. These free and bo-nd derivatives were tested for their coenzymic activities against several kinases. The activities of the ADP derivatives, V, VIII, X, XIII, dextran-bound VIII, and dextran-bound XIII against acetate kinase were 82%, 81%, 68%, 55%, 35%, and 15%, respectively, relative to ADP and those of the ATP derivatives, VI, IX, XI, XIV, dextran-bound IX, and dextran-bound XIV against hexokinase were 88%, 94%, 60%, 81%, 58%, and 49%, respectively, relative to ATP.

Adenosine Diphosphate↗