On the structure of the iron-sulfur complex in the two-iron ferredoxins

Recent spectroscopic and magnetic susceptibility studies of the iron center in the two-iron ferredoxins provide criteria which any model for the iron-sulfur complex in these proteins must satisfy. These criteria are most stringent for parsley and spinach ferredoxin: the reduced proteins contain a high-spin ferric atom antiferromagnetically exchange-coupled (presumably via sulfide bridging ligands) to a high-spin ferrous atom. In the oxidized proteins the iron atoms are antiferromagnetically spin-coupled, high-spin ferric atoms. Arguments are given to substantiate the claim that the ferrous atom in the reduced protein is ligated by four sulfur atoms in a distorted tetrahedral configuration: two are the bridging sulfides, two are cysteinyl sulfurs. A treatment of proton contact shifts based upon the above model is pertinent to proton magnetic resonance data already available and provides a means to identify directly the ligands at both iron atoms via further PMR experiments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33507/1/0000004.pd

Multiple frequency EPR studies on three forms of oxidized cytochrome c oxidase

Bovine heart mitochondrial cytochrome c oxidase (cytochrome aa3) (EC 1.9.3.1) has been demonstrated to occur in several forms when the redox centers in the protein are thought to be fully oxidized. We report here the results of extensive EPR studies at 3, 8.9, 9.2, 9.4, 15 and 34 GHz on the resting state, the alternative resting state (with g = 12 at 9 GHz) and pulsed state (with g = 5 signal at 9 GHz). Theoretical consideration is given to all binary spin-coupling possibilities under the constraint that the iron atoms are either ferric or ferrous and the copper atoms are either cupric or cuprous. We conclude that the g = 12 signal can arise from any spin system with S > 1 and |D| = 0.15 cm-1. The g = 5 signals originate from an excited, integer-spin system with |D| = 0.035 cm-1, which is approximately 7 cm-1 above the ground state (not observed in EPR). It is pointed out that in interpretations of data and elaboration of suitable models in this field, the implications of spin-coupling should be considered in a comprehensive and not in a selective way. At 3 GHz, EPR spectra of CuA in the resting, pulsed and anaerobically oxidized states show that this center is identical in its EPR for all three states.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25085/1/0000516.pd

On the nature of the iron sulfur cluster in a deuterated algal ferredoxin

A protonated and a completely deuterated two-iron algal ferredoxin from Synechococcus lividus have been studied by optical, electron paramagnetic resonance, electron-nuclear double resonance, proton magnetic resonance and Mossbauer spectroscopies; temperature dependent magnetic susceptibility measurements are reported as well. These studies have confirmed the electron localized model of the active center in the two-iron ferredoxins, as previously deduced from studies of spinach ferredoxin, have yielded much more precise spectroscopic parameters for this center, and have thus greatly increased the confidence in this model.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21928/1/0000335.pd

The two-iron ferredoxins in spinach, parsley, pig adrenal cortex, Azotobacter vinelandii, and Clostridium pasteurianum: Studies by magnetic field Mossbauer spectroscopy

The two-iron ferredoxins from spinach, parsley, Azotobacter vinelandii, Clostridium pasteurianum and the pig adrenal cortex were investigated by Mossbauer spectroscopy at temperatures from 4 to 256[deg]K and in magnetic fields up to 46 kGauss. Computational programs were devised to allow comparison of the experimental data with computer-simulated spectra in order to facilitate identification of the experimental spectral detail with specific Mossbauer spectroscopic parameters (quadrupole splittings, isomer shifts and nuclear hyperfine and nuclear Zeeman interactions). The results of the analysis permit the following properties of the active center to be established directly as the result of these experiments: 1. 1. In the oxidized forms of the proteins, each iron is in the high spin (S = 5/2) ferric state, spin-coupled to produce a resultant molecular diamagnetism for the protein at temperatures below 100[deg]K.2. 2. In the reduced state of the protein, the active center contains a single ferric site, retaining many properties of the ferric iron in the oxidized protein, but spincoupled to a high spin (S = 2) ferrous site, producing a molecular paramagnetism due to a net electron spin of one half at low temperatures (S = 1/2).3. 3. In spinach and parsley ferredoxins, the ligand symmetry around the ferrous site in the reduced form of the proteins is tetrahedral with measurable axial and rhombic distortions.4. 4. The iron sites in both the oxidized and reduced forms of all the proteins studied are similar, with the possible exception that the ligand symmetry at the ferrous site in the reduced form of the two-iron ferredoxins from C. pasteurianum, A. vinelandii (Azotobacter I and II), and pig adrenal cortex has not been characterized as being square planar or tetrahedral, although octahedral symmetry has been excluded.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33534/1/0000033.pd

An investigation of Chromatium vinosum high-potential irondashsulfur protein by EPR and Mossbauer spectroscopy; evidence for a freezing-induced dimerization in NaCl solutions

The high-potential irondashsulfur protein (HiPIP) from Chromatium vinosum contains a cubane prosthetic group that shuttles between the [4Fe-4S]3+,2+ states. We find that the EPR spectra from this protein can be explained as a sum of two components, a major one with g=2.02; 2.04; 2.12, and a minor one with g=2.04; 2.07; ~2.13. In the presence of 0.1-2.0 M NaCl, freezing induces polymerization of the protein (presumably dimers), which is detected as intercluster spindashspin interaction in the EPR. The observed spindashspin interactions are interpreted as being due to two very similar dimeric structures in an approx. 1:2 ratio. Computer simulation of the X- and Q-band EPR spectra shows that the z-components of the g-tensors in each dimer pair must be co-linear, with center-to-center distances between the clusters of ~ 13 A and ~ 16 A. Inspection of possible dimeric structures of C. vinosum HiPIP by standard molecular graphics procedures revealed that the Fe/S cluster is exposed toward a flattened surface and is accessible to solvent. Moreover, the Fe/S clusters in two HiPIP molecules can easily achieve a center-to-center distance of ~ 14 A when approaching along a common 3-fold axis that extends through the S4 sulfur atom of the cubane; the z-component of the EPR g-tensor is co-linear with this symmetry axis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29129/1/0000168.pd

Динамические тенденции в становлении предмета лингвоэкологии

Экологизация всех сфер общественной жизни и самого человека широко обсуждается во многих наука, а также и в области языка. Во многих работах лингвистов экология языка определяется как наука о взаимоотношениях между языком и его окружением, так как язык существует не только в сознании говорящих на нем и функционирует только при взаимоотношениях с другими коммуникантами и с их социальным и природным окружением. В этом контексте понятие «языковое сознание» представляет собой специфическую картину взаимосвязи культуры и общественной жизни социума, которая определяет его психологическое своеобразие и специфические черты данного языка

Tiered Approach to Resilience Assessment

Regulatory agencies have long adopted a three-tier framework for risk assessment. We build on this structure to propose a tiered approach for resilience assessment that can be integrated into the existing regulatory processes. Comprehensive approaches to assessing resilience at appropriate and operational scales, reconciling analytical complexity as needed with stakeholder needs and resources available, and ultimately creating actionable recommendations to enhance resilience are still lacking. Our proposed framework consists of tiers by which analysts can select resilience assessment and decision support tools to inform associated management actions relative to the scope and urgency of the risk and the capacity of resource managers to improve system resilience. The resilience management framework proposed is not intended to supplant either risk management or the many existing efforts of resilience quantification method development, but instead provide a guide to selecting tools that are appropriate for the given analytic need. The goal of this tiered approach is to intentionally parallel the tiered approach used in regulatory contexts so that resilience assessment might be more easily and quickly integrated into existing structures and with existing policies