Characterization of the heterogeneity of polyethylene glycol-modified superoxide dismutase by chromatographic and electrophoretic techniques.

Covalent attachment of polyethylene glycol (PEG) chains to the enzyme Cu,Zn-superoxide dismutase (SOD) produces a heterogeneous mixture of modified protein species. The heterogeneity of the product (PEG-SOD) derives from a variable stoichiometric combination of PEG with individual SOD molecules in addition to the polydispersity of the PEG reagent. Characterization of PEG-SOD presents significant challenges due in part to this heterogeneity in addition to the hybrid nature of the modified enzyme. The application of classical methods of protein characterization is not always successful for these PEG-proteins requiring the development of alternative or modified procedures. A series of chromatographic techniques including reversed-phase, ion-exchange, size-exclusion, and hydrophobic interaction high-performance liquid chromatography along with electrophoretic techniques including isoelectric focusing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and capillary zone electrophoresis have been developed for assessing the degree of heterogeneity of PEG-SOD samples which encompass a range of different stoichiometries. Examples will be given demonstrating the application of these techniques to characterize PEG-SOD samples of different composition produced during the course of the reaction between SOD and an activated PEG reagent.     

Production of π0 mesons and charged hadrons in\bar v neon and ν neon charged current interactions

The average multiplicities of charged hadrons and of π⁺, π^? and π⁰ mesons, produced in \(\bar v\) Ne and νNe charged current interactions in the forward and backward hemispheres of theW ^±-nucleon center of mass system, are studied with data from BEBC. The dependence of the multiplicities on the hadronic mass (W) and on the laboratory rapidity (y _Lab) and the energy fraction (z) of the pion is also investigated. Special care is taken to determine the π⁰ multiplicity accurately. The ratio of average π multiplicities \(\frac{{2\left\langle {n_{\pi ^O } } \right\rangle }}{{[\left\langle {n_{\pi ^ + } } \right\rangle + \left\langle {n_{\pi ^ - } } \right\rangle ]}}\) is consistent with 1. In the backward hemisphere \(\left\langle {n_{\pi ^O } } \right\rangle \) is positively correlated with the charged multiplicity. This correlation, as well as differences in multiplicities between \(\mathop v\limits^{( - )} \) and \(\mathop v\limits^{( - )} \) , \(\mathop v\limits^{( - )} \) scattering, is attributed to reinteractions inside the neon nucleus of the hadrons produced in the initial \(\mathop v\limits^{( - )} \) interaction.     

H2 Oxidation Electrocatalysis Enabled by Metal‐to‐Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction

Oxidation of H₂ in a fuel cell converts the chemical energy of the H?H bond into electricity. Electrocatalytic oxidation of H₂ by molecular catalysts typically requires one metal to perform multiple chemical steps: bind H₂, heterolytically cleave H₂, and then undergo two oxidation and two deprotonation steps. The electrocatalytic oxidation of H₂ by a cooperative system using Cp*Cr(CO)₃H and [Fe(diphosphine)(CO)₃]⁺ has now been invetigated. A key step of the proposed mechanism is a rarely observed metal‐to‐metal hydrogen atom transfer from the Cr?H complex to the Fe, forming an Fe?H complex that is deprotonated and then oxidized electrochemically. This “division of chemical labor” features Cr interacting with H₂ to cleave the H?H bond, while Fe interfaces with the electrode. Neither metal is required to heterolytically cleave H₂, so this system provides a very unusual example of a homolytic reaction being a key step in a molecular electrocatalytic process.     

Electron spin resonance studies of spin-labelled polymers—18: Adsorption of spin-labelled poly(vinyl acetate) on silica surfaces

The adsorption of spin-labelled poly(vinyl acetate) from dilute solutions in ethyl acetate, chloroform and toluene onto three silica adsorbents of different surface silanol contents was studied. The adsorption capacities of the three silica samples, which decreased with decreasing surface silanol content, were dependent on the nature of the solvent, being greatest in the poor solvent toluene and least in the good solvent ethyl acetate. The ESR spectra of the polymer adsorbed on the silica of highest silanol content suggested that the polymer had a relatively flat conformation when toluene or chloroform was solvent and a more looped conformation when ethyl acetate was solvent. With the silica of intermediate silanol content, the polymer adsorbed from chloroform solution also had a loopy conformation. The silica of lowest silanol content was prepared by treating the first silica absorbent with trimethylchlorosilane. The line-shapes in the ESR spectrum of the labelled polymer adsorbed on this modified silica indicated a change in mode of adsorption.     

Experimental test of the PCAC-hypothesis in charged current neutrino and antineutrino interactions on protons

Data obtained with the bubble chamber BEBC at CERN are used for the first significant test of Adler's prediction for the neutrino and antineutrino-proton scattering cross sections at vanishing four-momentum transfer squaredQ ². An Extended Vector Meson Dominance Model (EVDM) is applied to extrapolate Adler's prediction to experimentally accessible values ofQ ². The data show good agreement with Adler's prediction forQ ²→0 thus confirming the PCAC hypothesis in the kinematical region of high leptonic energy transfer ν>2 GeV. The good agreement of the data with the theoretical predictions also at higherQ ², where the EVDM terms are dominant, also supports this model. However, an EVDM calculation without PCAC is clearly ruled out by the data.     

Measurement of the structure functionsF 2 andxF 3 and comparison with QCD predictions including kinematical and dynamical higher twist effects

The isoscalar nucleon structure functionsF ₂(x, Q ²) andxF ₃(x, Q ²) are measured in the range 0<Q ²<64 GeV², 1.7<W ²<250 GeV²,x<0.7 using ν and \(\bar v\) interactions on neon in BEBC. The data are used to evaluate possible higher twist contributions and to determine their impact on the evaluation of the QCD parameter Λ. In contrast to previous analyses reaching to such lowW ² values, it is found that a low \(\Lambda _{\overline {MS} } \) value in the neighbourhood of 100 MeV describes the data adequately and that the contribution of dynamical higher twist effects is small and negative.     

Electron spin resonance studies of spin-labelled synthetic polymers part 12. The polymerisation of methyl methacrylate initiated by butyl lithium

It is shown that poly(methyl methacrylate), polymerised at 0° or above by butyl lithium in THF or toluene, contains a number of n-butyl isopropenyl ketone units. The α-methylenic protons on the n-butyl group of these units can be abstracted by the propagating or other reactive carbanion to yield the carbanionic species

This carbanion reacts with the “trap” 2-methyl-2-nitrosopropane to form, after hydrolysis and oxidation, the nitroxide label

the e.s.r. spectrum of which comprises a triplet of doublets.     

Ueber die Empfindlichkeit des Lackmuspapiers

Ohne Zusammenfassung     

Temperature and Solar Radiation Interactions on 3H-leucine Incorporation by Bacterioplankton in a Subtropical Estuary

Although the effects of UV radiation are thought to be temperature independent, the photoinhibition of aquatic bacteria may be temperature dependent owing to enzymatic repair kinetics, an important consideration for climate change analyses. We examined the interactions between temperature and solar radiation in water samples collected from the Blackwater River, Pensacola Bay, and the coastal Gulf of Mexico (Florida) in July 2008. Subsamples were incubated in the dark for 20 h at either the in situ temperature, +5°C from in situ or −5°C from in situ after which they were amended with ³H-leucine and irradiated in full sunlight at their respective temperatures and compared to samples incubated simultaneously in the dark. Temperature and light significantly affected ³H-leucine incorporation at all locations and interactive effects between temperature and sunlight were found for Pensacola Bay and the Gulf. Generally, warmer waters reduced photoinhibition. The −5°C treatment was always significantly more inhibited than the +5°C treatment, but the in situ temperature and +5°C and −5°C treatments were not always significantly different. Photoinhibition reduction at warmer temperatures suggests specific effects on photobiology not observed in general cellular activity may be important in determining interactive ecosystem effects of climate change.