Spectroscopic properties of Carcinus aestuarii hemocyanin and its structural subunits

Hemocyanin (Hc) of Carcinus aestuarii contains three major and one minor electrophoretically separable polypeptide chains which were purified by fast protein liquid chromatography (FPLC) ion exchange chromatography. N-terminal amino acid sequences of four structural subunits (SSs) from C. aestuarii were compared with known N-terminal sequences from other arthropodan hemocyanins. The conformational changes, induced by various treatments, were monitored by far UV, CD and fluorescence spectroscopy. The critical temperatures for the structural subunits, Tc, determined by fluorescence spectroscopy, are in the region of 52-59 degrees C and coincide with the melting temperatures, Tm (49-55 degrees C), determined by CD spectroscopy. The free energy of stabilization in water, delta GDH2O, toward guanidinium hydrochloride is about 1.3 times higher for the dodecameric Hc as compared to the isolated subunits and about one time higher for Cal, comparing with other SSs. The studies reveal that the conformational stability of the native dodecamer towards various denaturants (temperature and guanidinium hydrochloride) indicate that the quaternary structure is stabilized by oligomerization between structural subunits, and the possibility of a structural role of the sugar mojeties cannot be excluded.     

A novel Cu,Zn superoxide dismutase from the fungal strain Humicola lutea 110: isolation and physico-chemical characterization

The fungal strain Humicola lutea 110 produces a mangan- and a copper zinc-containing superoxide dismutases (SOD). In this study, the purification, N-terminal sequence and spectroscopic properties of the new Cu,Zn SOD are described. The preparation of the pure metalloenzyme was achieved via treatment of the strain with acetone followed by gel and ion exchange chromatography. The protein consists of 302 amino acid residues and has a molecular mass of approximately 32 kDa, as determined by PAG electrophoresis and 3100 U mg-1 protein-specific activity. It is a dimeric enzyme with two identical subunits of 15,950 Da, as indicated by SDS-PAGE, mass spectroscopic and amino acid analysis. The N-terminal sequence analysis of the Cu,Zn SOD from the fungal strain revealed a high degree of structural homology with enzymes from other eukaryotic sources. Conformational stability and reversibility of unfolding of the dimeric enzyme were determined by fluorescence and circular dichroism (CD) spectroscopy. The critical temperature of deviation from linearity (Tc) of the Arrhenius plot ln (Q-1(-1)) vs. 1/T was calculated to be 68 degrees C and the respective activation energy for the thermal deactivation of the excited indole chromophores is 42 kcal mol-1. The melting temperatures (Tm) were determined by CD measurements to be 69 degrees C for the holo- and 61 degrees C for the apo-enzyme. The fluorescence emission of the Cu,Zn SOD is dominated by 'buried' tryptophyl chromophores. Removal of the copper-dioxygen system from the active site caused a 4-fold increase of the fluorescence quantum yield and a 10 nm shift of the emission maximum position towards higher wavelength.     

Representation of the inverse of a frame multiplier

Certain mathematical objects appear in a lot of scientific disciplines, like physics, signal processing and, naturally, mathematics. In a general setting they can be described as frame multipliers, consisting of analysis, multiplication by a fixed sequence (called the symbol), and synthesis. In this paper we show a surprising result about the inverse of such operators, if any, as well as new results about a core concept of frame theory, dual frames. We show that for semi-normalized symbols, the inverse of any invertible frame multiplier can always be represented as a frame multiplier with the reciprocal symbol and dual frames of the given ones. Furthermore, one of those dual frames is uniquely determined and the other one can be arbitrarily chosen. We investigate sufficient conditions for the special case, when both dual frames can be chosen to be the canonical duals. In connection to the above, we show that the set of dual frames determines a frame uniquely. Furthermore, for a given frame, the union of all coefficients of its dual frames is dense in ?²${?}^2$. We also introduce a class of frames (called pseudo-coherent frames), which includes Gabor frames and coherent frames, and investigate invertible pseudo-coherent frame multipliers, allowing a classification for frame-type operators for these frames. Finally, we give a numerical example for the invertibility of multipliers in the Gabor case.     

Reversible transformations of gold nanoparticle morphology

Herein is reported a metamorphosis taking place in a gold nanosized system. The observed phenomenon of shape and size transformations was found to be completely reversible. Unlike most procedures in the literature where shape and size control occur in the synthetic step by adding growth- and shape-controlling agents such as surfactants or polymers, in this system postsynthetic changes in shape and size can be carried out simply by changing the ratio of reactive, competing reagents, more specifically, alkylthiols versus tetralkylammonium salts. Interestingly, the transfer of gold metal occurs (large prismatic particles to small particles and vice versa) under the influence of reagents that do not cause such interactions with bulk gold. All intermediate steps of the morphology change were observed using HRTEM and electron diffraction. The processes of breaking down and "welding back" solid metal nanoparticles occur under mild conditions and are remarkable examples of the unique chemical properties of nanomaterials. The described process is expected to be relevant to other nanoscale systems where similar structural circumstances could occur.     

Structural and spectroscopic studies of the native hemocyanin from Maia squinado and its structural subunits

The dodecameric hemocyanin of the crab Maia squinado contains five major electrophoretically separable polypeptide chains (structural subunits) which have been purified by FPLC ion exchange chromatography. The various proteins have been characterized by fluorescence spectroscopy, combined with fluorescence quenching studies, using acrylamide, caesium chloride and potassium iodide as tryptophan quenchers. The results show that the tryptophyl side chains of dodecameric Hc are deeply buried in hydrophobic regions of the hemocyanin aggregates and the quenching efficiency values for the native Hc in comparison with those from the constituent subunits are two to four times less. The conformational stabilities of the native dodecameric aggregate and its isolated structural subunits towards various denaturants (pH, temperature, guanidinium hydrochloride) indicate that the quaternary structure is stabilized by hydrophilic and polar forces, whereby, both, the oxy- and apo-forms of the protein have been considered. The critical temperatures for the structural subunits, Tc, determined by fluorescence spectroscopy, are in the region of 50-60 degrees C, coinciding with the melting temperatures, Tm, determined by CD spectroscopy. The free energy of stabilization in water, deltaG(D)H2O, toward guanidinium hydrochloride is about two times higher for the dodecamer as compared to the isolated subunits. These studies reveal that oligomerization between functional subunits has a stabilizing effect on the whole molecule and differences in the primary structures result in different stabilities of the subunits.     

Thermal behavior and characterization of solid-state chlorinated polyethylenes

The melting behavior of solid-state chlorinated polyethylene samples of various average molar mass has been studied by employing the differential scanning calorimetry method. Both the thermal and thermodynamic characteristics of the as-prepared chlorinated powdery polymer samples were found to be essentially different, compared to those of the melt-crystallized ones. The changes in the corresponding values depended mainly on the content of the comonomer units such as chloromethylene and dichloromethylene groups and their distribution along the polymer chains. Therefore, it can be assumed that the order of the polymer crystals arrangement is disturbed in the course of both the chlorination process and the subsequent melt crystallization.     

Neutron activation cross section for Ni isotopes at 14·8 MeV

Neutron activation cross sections for Ni isotopes were measured using Ge(Li)γ-ray spectroscopy of the reaction products. The linear least-squares method was used to resolve the interfering reactions. The results obtained are compared with recent experimental and evaluated data, statistical model and semiempirical calculations.     

Crystal growth, defect structure and magnetism of new Li3N-derived lithium nitridocobaltates

New nitridocobaltates Li(3-x-y)Co(x)N are revealed to contain significant Li(+) vacancies (y approximately 0.45) disordered within lithium-nitrogen planes and to exist as partially delocalised spin systems as a result of increased covalency through infinite -N-(Li,Co)-N- chains.