Photoreaction Cycle of Phoborhodopsin (Sensory Rhodopsin II) from Halobacterium salinarum Expressed in Escherichia coli

Phoborhodopsin (pR; also called sensory rhodopsin II, SRII) is a photoreceptor of negative phototaxis of halobacteria. The studies of photochemical properties of this pigment are not many because the amount of the pigment is small and the stability is low. Recently an expression system of phoborhodopsin from Halobacterium salinarum (called salinarum phoborhodopsin, spR; also HsSRII) in Escherichia coli and purification method has been developed (Mironova et al. [2005] FEBS Lett., 579, 3147–3151), which enables detailed studies on the photochemical properties of spR. In the present work, the photoreaction cycle of E. coli-expressed spR was studied by low-temperature spectroscopy and flash photolysis. Formations of K-, M-, O-like intermediates and P480 were reconfirmed as reported previously. New findings are as follows. (1) The K-like intermediate (P500) was a mixture of two photoproducts. (2) Formation of L-like intermediate (P482) was observed by low-temperature spectroscopy and flash photolysis at room temperature. (3) On long irradiation of spR at 20°C, formation of a new photoproduct P370 was observed and it decayed to the original spR in the dark with a decay half time of 190 min. Based on these results the similarities and dissimilarities between spR and ppR are discussed.     

Identification of Two Palmitoyl Groups in Octopus Rhodopsin

Abstract— We determined the structure and site of fatty acid incorporated in octopus rhodopsin using a combination of fluorescence label and enzymatic cleavage methods in conjunction with fast-atom bombardment (FAB) mass spectrometry. A single peptide containing two adjacent cysteines, Cys337 and Cys338, was successfully isolated using the fluorescence from a dye conjugated to Cys345. The FAB mass spectrometric analysis of the peptide (323phe-³⁴⁰phe) revealed that two palmitoyl groups are linked to Cys337 and Cys338 via thioester bonds in octopus rhodopsin as in bovine rhodopsin.     

Dehydrogenation of methanol to methyl formate over supported Ni, Pd and Pt catalysts. Anomalous catalytic functions of PdZn and PtZn alloys

Pd/ZnO and Pt/ZnO exhibited high catalytic performance for the dehydrogenation of methanol to methyl formate upon the formation of PdZn and PtZn alloys.     

Quinones synthesis via hydrogen peroxide oxidation of dihydroxy arenes catalyzed by homogeneous and macroporous-polymer-supported ruthenium catalysts

Ruthenium(II)/dimethyl phenyloxazoline (Ru(II)/dm-Pheox) complex 2a and its macroporous-polymeric-catalyst 4 were found to be very rapid and efficient catalysts in the hydrogen peroxide oxidation of 1,2- and 1,4-dihydroxy arenes. Most of the quinone products were delivered in 99% yield. The polymeric-catalyst 4 could be reused at least five times.     

Product analyses and crosslink mechanism of plasma-polymerized methyl methacrylate

Plasma-polymerized methyl methacrylate (PPMMA) film was produced by a radio-frequency glow discharge of methyl methacrylate (MMA) gas with argon. PPMMA deposited under a plasma of mild energy was separated into a soluble fraction (sol-PPMMA) and an insoluble matrix (insol-PPMMA), which is highly crosslinked, by solvent-extraction and filtration. The chemical structure of the sol-PPMMA was determined by pyrolysis/gas chromatography, IR spectroscopy, ¹H-NMR, ¹³C-NMR, and elemental analysis techniques. On the other hand, the structure of the insol-PPMMA was examined with IR spectroscopy, ¹³C-NMR with CP/MAS method, and elemental analysis. The crosslinking mechanism in the plasma polymerization of MMA is discussed on the basis of product analyses of the sol-PPMMA and the insol-PPMMA.     

Synthesis and antifungal activities of a series of (1,2-disubstituted vinyl)imidazoles.

A series of vinylimidazoles containing a hetero atom such as sulfur or oxygen at a beta-position of the vinyl group was prepared and the antifungal activities were tested. It was found that sulfur-substituted derivatives such as (E)-1-[2-(methylthio)-1-[2-(pentyloxy)phenyl]ethenyl]-1H-imidazole (5a-5) and (E)-1-[1-[2-(hexyloxy)phenyl]-2-(methylthio)ethenyl]-1H-imidazole (5a-6) showed excellent antifungal activities against dermatophytes and yeast cells. The stereochemistry of the hydrochloride salt of 5a-5 was determined by X-ray crystallography. The structure-activity relationships were discussed.     

QUANTUM EFFICIENCY FOR THE PHOTOCONVERSION OF BACTERIORHODOPSIN AT VERY LOW TEMPERATURES

Abstract— Quantum efficiencies for photoconversion of bacteriorhodopsin (trans-bR) to a bathochromic product (batho-bR^t) and its photoreversion in purple membrane at 77 and 9 K were investigated with low temperature spectrophotometry. The kinetics of the photoconversion and its photoreversion cannot be expressed by a single exponential curve. The photoconversions at 77 and 9 K showed the same slope in the early stage. The kinetics of the photoreversions were identical at the two temperatures. These results indicate that the quantum efficiencies for the conversion of trans-bR to batho-bR^t or for its photoreversion are identical at the two temperatures.
The fact that the photoreversion cannot be expressed by a single exponential curve suggests the existence of several conformational states of batho-bR^t due to the trimer structure of the purple membrane.     

Quasi-elastic scattering of the proton drip line nucleus 17F on 12C at 60 MeV

The quasi-elastic scattering angular distribution of the proton drip line nucleus ¹⁷F on a ¹²C target was measured at 60 MeV. The experimental data have been compared with the theoretical analysis based onto optical model and continuum discretized coupled channels (CDCC). The couplings between breakup and elastic scattering channels, and between inelastic and elastic scattering channels resulted very weak. In order to explore the breakup effects the total reaction cross-section was deduced from the angular distribution of the quasi-elastic scattering data, and then compared with the existing data for the other weakly and tightly bound nuclei on ¹²C target using a universal function. From this comparison, we concluded that the breakup effect is not important for weakly bound projectiles on the light target as obtained also with the CDCC analysis.     

Specific heat measurement of the layered nitride superconductor Li(x)ZrNCl

Specific heat has been investigated in a layered nitride superconductor, Li(0.12)ZrNCl, with T(c)=12.7 K. The obtained data have shown a marked dichotomy: The specific heat jump at T(c) (DeltaC/gamma(n)T(c)=1.8) and the superconducting gap ratio (2Delta/k(B)T(c)=4.6-5.2) have indicated an intermediate to a strong coupling of electrons, while the upper limit of the electron-phonon coupling constant lambda has directly been estimated to be 0.22, which belongs to a weak coupling regime. Furthermore, the rapid increase of gamma as a function of magnetic field suggests that the present material has an anisotropic s wave gap.     

Enantioselective gem-chlorofluorination of active methylene compounds using a chiral spiro oxazoline ligand

Highly enantioselective gem-chlorofluorination of active methylene compounds was carried out by using a copper(II) complex of a chiral spiro pyridyl monooxazoline ligand. This reaction yielded α-chloro-α-fluoro-β-keto esters and α-chloro-α-fluoro-β-keto phosphonates with up to 92% ee. The resulting dihalo β-keto ester was converted into various α-fluoro-α-heteroatom-substituted carbonyl compounds via nucleophilic substitution without loss of optical purity. A fully protected β-amino acid with a gem-chlorofluoromethylene function was also synthesized.