How can a single second sphere amino acid substitution cause reduction midpoint potential changes of hundreds of millivolts?

The active site metal ion of superoxide dismutase (SOD) is reduced and reoxidized as it disproportionates superoxide to dioxygen and hydrogen peroxide. Thus, the reduction midpoint potential (Em) is a critical determinant of catalytic activity. In E. coli Fe-containing SOD (FeSOD), reduction of Fe3+ is accompanied by protonation of a coordinated OH-, to produce Fe2+ coordinated by H2O. The coordinated solvent's only contact with the protein beyond the active site is a conserved Gln residue. Mutation of this Gln to His or Glu resulted in elevation of the Em by 220 mV and more than 660 mV, respectively [Yikilmaz et al., Biochemistry 2006, 45, 1151-1161], despite the fact that overall protein structure was preserved, His is a chemically conservative replacement for Gln, and neutral Glu is isostructural and isoelectronic with Gln. Therefore, we have investigated several possible bases for the elevated Em's, including altered Fe electronic structure, altered active site electrostatics, altered H-bonding and altered redox-coupled proton transfer. Using EPR, MCD, and NMR spectroscopies, we find that the active site electronic structures of the two mutants resemble that of the WT enzyme, for both oxidation states, and Q69E-FeSOD's apparent deviation from WT-like Fe3+ coordination in the oxidized state can be explained by increased affinity for a small anion. Spontaneous coordination of an exogenous anion can only stabilize oxidized Q69E-Fe3+SOD and, therefore, cannot account for the increased Em of Q69E FeSOD. WT-like anion binding affinities and active site pK's indicate that His69 of Q69H-FeSOD is neutral in both oxidation states, like Gln69 of WT-FeSOD, whereas Glu69 appears to be neutral in the oxidized state but ionized in the reduced state of Q69E-FeSOD. A 1.1 A resolution crystal structure of Q69E-Fe2+SOD indicates that Glu69 accepts a strong H-bond from coordinated solvent in the reduced state, in contrast to the case in WT-FeSOD where Gln69 donates an H-bond. These data and DFT calculations lead to the proposal that the elevated Em of Q69E-FeSOD can be substantially explained by (1) relief from enforced H-bond donation in the reduced state, (2) Glu69's capacity to provide a proton for proton-coupled Fe3+ reduction, and (3) strong hydrogen bond acceptance in the reduced state, which stabilizes coordinated H2O. Our results thus support the hypothesis that the protein matrix can apply significant redox tuning via its influence over redox-coupled proton transfer and the energy associated with it.     

Electrochemiluminescent detection of labile radical intermediates of electrochemical reactions

The article considers the basic principles of electrochemiluminescent spin traps diagnostic method which consists of efficient trapping of intermediate labile radical products (free radicals of complex organic molecules) by electrogenerated radical ions of electrochemiluminescers in different liquid-phase systems including bioobjects. The method permits qualitative and quantitative identification of such particles by measurement of electrolysis radical recombination luminescence (electrogenerated chemiluminescence) intensity which is emitted by electrolyzed solutions of organic electrochemiluminescers. The unique possibilities of the method are illustrated on examples of experimental study of systems with sodium tetraphenylborate and chloride ion.     

Hydroxy and Methoxy Substituted Thiacarbocyanines for Fluorescent Detection of Amyloid Formations

In present paper series of trimethine cyanines modified in 5,5′- or 6,6′- position with hydroxy- or methoxy- substituents is studied for their ability to interact selectively with fibrillar formations. Processes of dye aggregation that accompany this interaction were also investigated. Meso-methyl trimethynecyanines with 5,5′- methoxy (7519) and hydroxy (7515) substituents strongly (up to 40 times) increase fluorescence intensity in the presence of fibrillar insulin, and also give noticeable fluorescent response on the presence of various aggregated proteins (lysozyme, β-lactoglobulin, α-synuclein A53T). 7519 and 7515 dyes can be used for fluorometric detection of fibrillar insulin at concentrations of approximately 1.5–120 microg/ml. For meso-ethyl substituted dye 7514 the ability to form H- and J-aggregates upon interaction with insulin fibrils was suggested. The model of the H- and J-aggregate packing in the protein fibrillar structure has been proposed.     

Convergence in <Emphasis Type="Italic">L</Emphasis><Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>([0, <Emphasis Type="Italic">T</Emphasis>]) of Wavelet Expansions of <Emphasis Type="Italic">φ</Emphasis>-Sub-Gaussian Random Processes

The article presents new results on convergence in L _p ([0,T]) of wavelet expansions of φ-sub-Gaussian random processes. The convergence rate of the expansions is obtained. Specifications of the obtained results are discussed.     

Mass‐Spectrometric Studies of Providencia SR‐Form Lipopolysaccharides and Elucidation of the Biological Repeating Unit Structure of Providencia rustigianii O14‐Polysaccharide

Enterobacteria Providencia are opportunistic human pathogens causing multiple types of infections. Earlier we have studied the S‐ and R‐form lipopolysaccharides (LPSs) of Providencia strains of various O‐serogroups and established the structures of the O‐polysaccharides (O‐antigens) and core‐region oligosaccharides, respectively. Now we report on mass spectrometric studies of oligosaccharides consisting of the core moiety with one O‐polysaccharide repeating unit attached, which were derived from the SR‐form LPSs of Providencia strains. The site of attachment of the O‐polysaccharide to the core and the structure of the O‐polysaccharide biological repeating unit were elucidated in Providencia rustigianii O14 using NMR spectroscopy.     

2-Oxo-2-polyfluoroalkylethane-1-sulfones and -sulfamides in the Biginelli and ‘retro-Biginelli’ reactions

2-Oxo-2-polyfluoroalkylethane-1-sulfones and -sulfamides react with aryl aldehydes and urea under Biginelli reaction conditions to yield 4-hydroxy-4-polyfluoroalkyl-5-sulfonyl-6-aryl-tetrahydropyrimidinones. The latter compounds on reaction with hexamethylenetetramine (HMTA) under thermal conditions undergo ‘retro-Biginelli’ reaction involving replacement of the 6-aryl substituent of the pyrimidinone cycle with a hydrogen atom donated by HMTA. Hexamethylenetetramine was employed for the first time in place of formaldehyde in the reported one-step Biginelli protocol for the synthesis of fluorinated sulfonyl-containing 6-unsubstituted tetrahydropyrimidinones.     

Dynamics of nanoparticles in a supercooled liquid

The dynamic properties of nanoparticles suspended in a supercooled glass forming liquid are studied by x-ray photon correlation spectroscopy. While at high temperatures the particles undergo Brownian motion the measurements closer to the glass transition indicate hyperdiffusive behavior. In this state the dynamics is independent of the local structural arrangement of nanoparticles, suggesting a cooperative behavior governed by the near-vitreous solvent.