Selective oxidative destruction of iron-sulfur clusters Ferricyanide oxidation of Azotobacter vinelandii ferredoxin I

AbstractThe destructive oxidation of aerobically isolated 7Fe Azotobacter vinelandii ferredoxin I [(7Fe)FdI] by Fe(CN)63− is examined using low-temperature magnetic circular dichroism (MCD) and EPR. The results demonstrate that oxidation of the [3Fe-3S] cluster occurs only after essentially complete destruction of the [4Fe-4S] cluster. It is therefore feasible by controlled Fe(CN)63− oxidation to obtain a partially metallated form of FdI, (3Fe)FdI, containing only a [3Fe-3S) cluster. The MCD and EPR data demonstrate that the [3Fe-3S] cluster in (3Fe)FdI is essentially identical in structure to that in the native protein

Breakup Reactions of 11Li within a Three-Body Model

We use a three-body model to investigate breakup reactions of 11Li (n+n+9Li) on a light target. The interaction parameters are constrained by known properties of the two-body subsystems, the 11Li binding energy and fragmentation data. The remaining degrees of freedom are discussed. The projectile-target interactions are described by phenomenological optical potentials. The model predicts dependence on beam energy and target, differences between longitudinal and transverse momentum distributions and provides absolute values for all computed differential cross sections. We give an almost complete series of observables and compare with corresponding measurements. Remarkably good agreement is obtained. The relative neutron-9Li p-wave content is about 40%. A p-resonance, consistent with measurements at about 0.5 MeV of width about 0.4 MeV, seems to be necessary. The widths of the momentum distributions are insensitive to target and beam energy with a tendency to increase towards lower energies. The transverse momentum distributions are broader than the longitudinal due to the diffraction process. The absolute values of the cross sections follow the neutron-target cross sections and increase strongly for beam energies decreasing below 100 MeV/u.Comment: 19 pages, 14 figures, RevTeX, psfig.st

The Interaction of αB-Crystallin with Mature α-Synuclein Amyloid Fibrils Inhibits Their Elongation

αB-Crystallin is a small heat-shock protein (sHsp) that is colocalized with α-synuclein (αSyn) in Lewy bodies—the pathological hallmarks of Parkinson's disease—and is an inhibitor of αSyn amyloid fibril formation in an ATP-independent manner in vitro. We have investigated the mechanism underlying the inhibitory action of sHsps, and here we establish, by means of a variety of biophysical techniques including immunogold labeling and nuclear magnetic resonance spectroscopy, that αB-crystallin interacts with αSyn, binding along the length of mature amyloid fibrils. By measurement of seeded fibril elongation kinetics, both in solution and on a surface using a quartz crystal microbalance, this binding is shown to strongly inhibit further growth of the fibrils. The binding is also demonstrated to shift the monomer-fibril equilibrium in favor of dissociation. We believe that this mechanism, by which a sHsp interacts with mature amyloid fibrils, could represent an additional and potentially generic means by which at least some chaperones protect against amyloid aggregation and limit the onset of misfolding diseases

Genetic, abiotic and social influences on sex differentiation in cichlid fishes and the evolution of sequential hermaphroditism

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73799/1/j.1467-2979.2005.00184.x.pd

Vascular Remodeling in Health and Disease

The term vascular remodeling is commonly used to define the structural changes in blood vessel geometry that occur in response to long-term physiologic alterations in blood flow or in response to vessel wall injury brought about by trauma or underlying cardiovascular diseases.1, 2, 3, 4 The process of remodeling, which begins as an adaptive response to long-term hemodynamic alterations such as elevated shear stress or increased intravascular pressure, may eventually become maladaptive, leading to impaired vascular function. The vascular endothelium, owing to its location lining the lumen of blood vessels, plays a pivotal role in regulation of all aspects of vascular function and homeostasis.5 Thus, not surprisingly, endothelial dysfunction has been recognized as the harbinger of all major cardiovascular diseases such as hypertension, atherosclerosis, and diabetes.6, 7, 8 The endothelium elaborates a variety of substances that influence vascular tone and protect the vessel wall against inflammatory cell adhesion, thrombus formation, and vascular cell proliferation.8, 9, 10 Among the primary biologic mediators emanating from the endothelium is nitric oxide (NO) and the arachidonic acid metabolite prostacyclin [prostaglandin I2 (PGI2)], which exert powerful vasodilatory, antiadhesive, and antiproliferative effects in the vessel wall

A TEST OF THE INTRINSIC NATURE OF THE SHALLOW PROTON TRAPS IN ICE

It was recently suggested by Warman and Kunst that the slow secondary decay of solvated electrons, generated in ice by pulsed-electron-beam radiolysis, is indicative of the presence of relatively shallow proton traps that delays the non-geminate recombination of proton-solvated electron pairs (1). Their model for the kinetics of the decay of e- (sol), which extends into the microsecond range at 270 K invoked the presence of a pseudoequilibrium between mobile protons and protons immobilized by association with shallow traps. The traps were tentatively identified as Bjerrum L-defects which are known to have an associated partial negative charge (2). Additional strong evidence, for the importance of shallow proton traps in ice following radiolysis, was subsequently obtained from FT-IR spectroscopic study of proton exchange rates as a function of temperature (3). Although irradiation with 1.7 MeV electrons produced only limited proton exchange in cubic ice at 90 K, the subsequent warming of the samples into the 125 K range resulted in the rapid conversion of isolated D2O to neighbor coupled HOD molecules. Since the thermal generation of the mobile protons required for this exchange reaction requires temperatures in excess of 135 K and results in the formation of isolated HOD (4), protons escaping from shallow traps were clearly responsible for the 125 K reaction. Since electron beam radiolysis generates numerous defects in ice and, when prolonged, can convert crystalline ice to amorphous ice, the rather conclusive evidence that protons are shallowly trapped in ice following radiolysis is only suggestive of the existence of such traps in pure ice. On the other hand, the question of the intrinsic or extrinsic nature of the traps is of considerable consequence in the analysis of both kinetic and thermodynamic properties of ion-pair defects in ice. For these reasons efforts to evaluate the nature of the shallow traps are warranted and one such effort, based on the photoionization of ice, is described

FT-IR SPECTRA OF VACUUM DEPOSITED CLATHRATE HYDRATES OF OXIRANE, H2S, THF, ETHANE AND CYCLOPROPANE

An ability to prepare clathrate hydrates using low temperature-high vacuum techniques, originally demonstrated for the hydrate of oxirane (Bertie and Devlin), has been extended to include the structure I hydrate of cyclopropane and H2S, mixed structure I hydrate of oxirane and ethane as well as the structure II simple hydrate of THP and the double hydrates of THF with oxirane and cyclopropane. The crystalline clathrate films (~ 6 µ) have been formed either by annealing amorphous host-guest deposits at ~ 130 K, epitaxial growth at 110 K (oxirane and mixed ethane-oxirane or direct deposition at 150 K (THF and its double clathrates). Use of the epitaxial approach at 100 K has permitted the formation of the oxirane clathrate hydrate containing intact isolated D2O molecules. This has permitted the FT-IR observation of the v3-v1 doublet in the O-D stretching region (2455 cm-1 and 2380 cm-1 at 100 K) with the values, after correction for Fermi resonance, suggesting a splitting from intramolecular coupling of ~ 56 cm-1 (2455 cm-1 vs. 2399 cm-1), which compares closely with the 52 cm-1 deduced for cubic ice. Spectra for the structure I hydrates of oxirane and H2S contain adsorption bands produced by guest molecules confined to both small and large clathrate cages. Use of the structure II double hydrates has permitted the firm identification of the structure I infrared bands with oxirane and H2S molecules in cages of one size or the other. Thus, the weaker v3 and (v11, v14) bands of oxirane at 1281 and 1152 cm-1 have been assigned to molecules in the small cages since only these oxirane features remain in the structure II double hydrate with THF. In this case the smaller oxirane molecules occupy the small cages while the THF molecules enter the larger cages, exclusively. In a similar manner, the H-S stretching vibrations of H2S in the structure I small cages have been assigned to a band complex near 2610 cm-1, some 50 cm-1 above the band system for H2S in the large structure I clathrate cages. Such a result suggests that the net H2S perturbation, relative to the gas phase, is greater for the large than for the small cages and may be interpreted as evidence for a "double well" large cage potential or as further evidence that the cage model of Pimentel and Charles for guest molecule stretching modes is valid