CHROMOPHORE ROTATION IN 124-kD ALTON A vena sativa PHYTOCHROME AS MEASURED BY LIGHT-INDUCED CHANGES IN LINEAR DICHROISM

Abstract— From light-induced changes in linear dichroism, we have calculated the rotation of the long-wavelength-absorbing transition moment that occurs during phototransformation of 124-kilodalton Avena sativa phytochrome. Phytochrome was purified to homogeneity and immobilized onto Sepharose beads covalently coated with antibodies against A. sativa phytochrome. Changes in linear dichroism were induced by plane-polarized red or far-red light and measured by the absorbance differences at 660 and 730 nm using a dual-wavelength spectrophotometer equipped with polarizing filters in the measuring beams. From such measurements, we calculate a rotation angle of 31^o (or 149^o) during photoconversion of Pr to Pfr and 30^o (or 150^o) during photoconversion of Pfr to Pr. These values are similar to the value of 32^o (or 148^o) reported earlier for the rotation of the transition moment of "large" A. sativa phytochrome (∽ 120 kilodalton) isolated under conditions that did not preclude post homogenization proteolysis of the 124 kilodalton molecule.     

Partial least-squares regression and fuzzy clustering — A joint approach

Chemical and physical analyses of malt, the main ingredient of beer, have been used to predict the concentration of certain volatile compounds in the finished beer.The prediction was done by means of the partial least squares regression (PLS2) in SIMCA. The total data set as well as individual malt clusters were submitted to PLS analysis. Best prediction was obtained by separating the total object matrix in classes according to similarity found by fuzzy pattern recognition (FCV). FCV was also used to separate the beer variables in classes and to select the subset of variables to be predicted.A joint approach of fuzzy pattern recognition to identify groups of samples and SIMCA-PLS2 to predict several dependent variables is suggested as a powerful tool in process-analytical chemistry.     

Germanium-oxygen interactions in acyl-substituted germyleneazines L2GeNNC(COX)(COY)

MNDO calculations have been carried out on the reactions of the electron-rich germylene L₂Ge [L=(H₃Si)₂N] with diazo compounds, as models for the experimentally observed reactions of L₂Ge [L=(Me₃Si)₂N]. The most stable form of the 11 adduct of L₂Ge with N₂C(COOMe)₂ is found to have a cyclic configuration resulting from a strong intramolecular interaction between the oxygen of one of the carbonyl groups and the germanium atom. Protonation of this cyclic adduct occurs at nitrogen, giving an intermediate, addition to which of nucleophiles X^– provides acyclic L₂Ge(X)NHN(COOMe)₂, as observed experimentally. Two similar cyclic adducts are formed between L₂Ge and N₂C(COCH₃)(COOCH₃), the most stable of which provides, after a proton shift, the observed 1,3,4,2-oxadiazagermine system . Adduct formation between Me₂Si=NSiMe₃ and simple Lewis bases (H₂O, NH₃, THF, H₂CO) is calculated to be strong, but the corresponding adducts of Me₂Ge=NSiMe₃ are very weak: much stronger adducts are predicted for L₂GeNNC(COOMe)₂.     

A new class of low-molecular-weight amphiphilic gelators

A new powerful class of low-molecular-weight amphiphilic compounds has been synthesized and their structure-property relationships with respect to their gelation ability of organic solvents have been investigated. These compounds are able to gel organic solvents over a broad range of polarity. Especially polar solvents such as valeronitrile and gamma-butyrolactone can be gelled even at concentrations far below 1 wt %. It was found that the gelation ability of these asymmetrically substituted p-phenylendiamines depends on a well-balanced relation of the terminal head group, the units involved in hydrogen bonding (amide or urea groups), and on the length of the alkyl chain. With this class of new gelators it is possible to tailor thermal and mechanical properties in different organic solvents and open various application possibilities.     

Constant-cutoff approach to soliton polarizabilities

The static electromagnetic polarizabilities of nucleons and -particles are calculated in the simplified Skyrme model, where the quartic Skyrme stabilizing term is omitted and where the constant-cutoff stabilization method is used to stabilize the Skyrme soliton. The numerical results are of the same accuracy as those obtained using the complete Skyrme model, but the simplified Skyrme model offers simpler mathematical structure and easier calculations.     

Preparation and partial characterization of a soluble site-to-site directed enzyme complex composed of alcohol dehydrogenase and lactate dehydrogenase

A soluble, bifunctional enzyme complex has been prepared by crosslinking lactate dehydrogenase and alcohol dehydrogenase with glutaraldehyde. The crosslinking was performed on a solid phase while the active sites of alcohol dehydrogenase and lactate dehydrogenase were held adjacent to one another with the aid of a bis-NAD analog. Subsequently, the enzyme complex was released from the solid phase. The soluble enzyme complex was then purified by using NAD-Sepharose as an affinity adsorbent. Based on gel filtration experiments, the complex was estimated to consist of one of each dehydrogenase. By using a third enzyme, lipoamide dehydrogenase, which competes with lactate dehydrogenase for NADH produced by alcohol dehydrogenase, the effect of site-to-site orientation was studied. It was found that about 83% of the NADH produced by alcohol dehydrogenase was oxidized by site-to-site oriented lactate dehydrogenase compared to a figure of only about 61% obtained in an identical system of separate enzymes. This indicates that given two alternative routes, the preference for the one to lactate dehydrogenase over the one to lipoamide dehydrogenase is enhanced when lactate dehydrogenase and alcohol dehydrogenase are site-to-site oriented.     

Photobiological characteristics and photosynthetic UV responses in two Ulva species (Chlorophyta) from southern Spain

The effect of different wavebands of artificial UV (UVB and UVA) and photosynthetically active radiation (PAR) was assessed in two species of the genus Ulva, U. olivascens and U. rotundata, from southern Spain in order to test for possible differences in acclimation of photosynthesis. Both species share similar morphology but are subject to different light environments: U. rotundata is an estuarine alga, inhabiting subtidal locations, while U. olivascens is an intertidal, sun-adapted organism. Algae were exposed to three different UV conditions, PAR+UVA+UVB, PAR+UVA and PAR for 7 d. Short-term exposure (6 h) was also carried out, using two PAR levels, 150 and 700 micromolm(-2)s(-1). Pigment contents and photosynthesis vs. irradiance curves from oxygen evolution were used to contrast sun- and shade adaptation between these species. O2-based net photosynthesis (Pmax) and PAM-chlorophyll fluorescence (optimal quantum yield, Fv/Fm) were used as parameters to evaluate photoinhibition of photosynthesis in the experiments. The results underline different photobiological characteristics among species: the subtidal U. rotundata had higher contents of pigments (Chl a, Chl b and carotenoids) than the sun-adapted U. olivascens, which resulted in higher thallus absorptance and P-I parameters characterized by higher photosynthetic efficiency at limiting irradiances (alpha) and lower saturating points for photosynthesis (Ek). After 7 d exposure, photoinhibition of Fv/Fm was close to 40-45% in both species. Differences between UV treatments were seen in U. rotundata after 5 d and after 7 d in U. olivascens, in which PAR+UVA impaired strongly photosynthesis (80%). Such patterns were correlated with a progressive decrease in pigment contents, specially chlorophylls. In short-term (6 h) exposures, combinations of UVA+UVB and high PAR level resulted in high rates of photoinhibition of chlorophyll fluorescence (68-92%) in U. rotundata, whereas in U. olivascens photoinhibition ranged between 42% and 53%. Photoinhibition under low PAR combined to UV radiation was lower than observed under high PAR. Net O2-Pmax revealed similar response among the species, with maximal photoinhibition rates close to 60% in algae incubated under high PAR+UVA+UVB. In the case of UV exposure in combination with low PAR, the highest photoinhibition rates were measured in U. rotundata.     

Binding behaviour and conformational properties of globular proteins in the presence of immobilised non-polar ligands used in reversed-phase liquid chromatography

The thermodynamic and extra-thermodynamic dependencies of five types of cytochrome c in water-acetonitrile mixtures of different composition in the presence of immobilised n-octyl ligands as a function of temperature from 278 K to 338 K have been investigated. The corresponding enthalpic, entropic and heat capacity parameters, deltaHdegrees assoc, deltaS degrees assoc and delta C degrees p, have been evaluated from the observed non-linear Van't Hoff plots of these globular proteins in these heterogeneous systems. The relationships between the free energy dependencies, various molecular parameters and extra-thermodynamic dependencies (empirical correlations) of these protein-non-polar ligand interactions have also been examined. Thus, the involvement of enthalpy-entropy compensation effects has been documented for the binding of these cytochrome cs to solvated n-octyl ligands. Moreover, the results confirm that this experimental approach permits changes in molecular surface area due to the unfolding of these proteins on association with non-polar ligands as a function of temperature to be correlated with other biophysical properties. This study thus provides a general procedure whereby the corresponding free energy dependencies of globular proteins on association with solvated non-polar ligands in heterogeneous two-phase systems can be quantitatively evaluated in terms of fundamental molecular parameters.