Biomedical subjects

Susumu Yoshikawa

Publications and source records attributed to Susumu Yoshikawa.

8 recordsLinked to original sources

PubMed2006

Comparison of electrode structures and photovoltaic properties of porphyrin-sensitized solar cells with TiO2 and Nb, Ge, Zr-added TiO2 composite electrodes.

Electrode structures and photovoltaic properties of porphyrin-sensitized solar cells with TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were examined to disclose the effects of partial substitution of Ti atom by the other metals in the composite electrodes. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were prepared by sol-gel process using laurylamine hydrochloride as a template for the formation of micellar precursors yielding well-defined mesoporous nanocrystalline structures, as in the cases of the formation of silica and titania tubules and nanoparticles by the templating mechanism. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were characterized by transmission electron microscopy, BET surface area analysis, X-ray diffraction analysis, Raman spectroscopy, and impedance measurements. The TiO2 anatase nanocrystalline structure is retained after doping a small amount (5 mol %) of Nb, Ge, or Zr into the TiO2 structure, suggesting the homogeneous distribution of the doped metals with replacing Ti atom by the doped metal. The power conversion efficiency of the porphyrin-sensitized solar cells increases in the order Zr-added TiO2 (0.8%) < Nb-added TiO2 (1.2%) < TiO2 (2.0%) < Ge-added TiO2 cells (2.4%) under the same conditions. The improvement of cell performance of the Ge-added TiO2 cell results from the negative shift of the conduction band of the Ge-added TiO2 electrode. The Ge-added TiO2 cell exhibited a maximum power conversion efficiency of 3.5% when the porphyrin was adsorbed onto the surface of the Ge-added TiO2 electrode with a thickness of 4 microm in MeOH for 1 h.

Journal Article↗

PubMed2006

A simple route utilizing surfactant-assisted templating sol-gel process for synthesis of mesoporous Dy2O3 nanocrystal.

A simple route of combined sol-gel process with surfactant-assisted templating technique was successfully employed for the first time to synthesize nanocrystalline mesoporous Dy(2)O(3) with narrow monomodal pore size distribution under mild conditions. The nanocrystalline Dy(2)O(3) with monomodal mesoporous characteristic was ultimately achieved by controlling the hydrolysis and condensation steps of dysprosium n-butoxide modified with acetylacetone in the presence of laurylamine hydrochloride surfactant aqueous solution. The synthesized material was methodically characterized by thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), N(2) adsorption-desorption, Brunauer-Emmett-Teller (BET) surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size distribution analysis. The particle size of the synthesized Dy(2)O(3) in nanosized range obtained from the SEM and HRTEM micrographs was in good accordance with the crystallite size estimated from the XRD result. The N(2) adsorption-desorption result exhibited hysteresis pattern with single loop, indicating the existence of monomodal mesopore. The extremely narrow pore size distribution with mean pore diameter in the mesopore region of the synthesized Dy(2)O(3) was also confirmed by the BJH result.

Journal Article↗

PubMed2005

Dual DNA recognition codes of a short peptide derived from the basic leucine zipper protein EmBP1.

Sequence-specific DNA binding of short peptide dimers derived from a plant basic leucine zipper protein EmBP1 was studied. A homodimer of the EmBP1 basic region peptide recognized a palindromic DNA sequence, and a heterodimer of EmBP1 and GCN4 basic region peptides targets a non-palindromic DNA sequence when a beta-cyclodextrin/adamantane complex is utilized as a dimerization domain. A homodimer of the EmBP1 basic region peptide binds the native EmBP1 binding 5'-GCCACGTGGC-3' and the native GCN4 binding 5'-ATGACGTCAT-3' sequences with almost equal affinity in the alpha-helical conformation, indicating that the basic region of EmBP1 by itself has a dual recognition codes for the DNA sequences. The GCN4 basic region peptide binds 5'-ATGAC-3' in the alpha-helical conformation, but it neither shows affinity nor helix formation with 5'-GCCAC-3'. Because native EmBP1 forms 100 times more stable complex with 5'-GCCACGTGGC-3' over 5'-ATGACGTCAT-3', our results suggest that the sequence-selectivity of native EmBP1 is dictated by the structure of leucine zipper dimerization domain including the hinge region spanning between the basic region and the leucine zipper.

Amino Acid Sequence↗

PubMed2005

Ribonucleopeptides recognize the phosphotyrosine residue.

Tools for selective recognition and sensing of kinase-catalyzed phosphorylation of Tyr or Ser/Thr residues located on a protein surface are essential for understanding signal transduction cascades of living cell. A stable complex of RNA and peptide (ribonucleopeptide) provides a new approach to tailor a receptor for small molecules. In vitro selection of an RNA-derived pool of ribonucleopeptide afforded a ribonucleopeptide receptor specific for phosphotyrosine (pTyr). Moreover, the ribonucleopeptide receptors are conveniently converted to fluorescent sensors for pTyr.

Binding Sites↗

PubMed2004

De novo design, synthesis, and function of semiartificial myoglobin conjugated with coiled-coil two-alpha-helix peptides.

The introduction of a flavin chromophore on the myoglobin (Mb) surface and an effective electron-transfer (ET) reaction through the flavin were successfully achieved by utilizing the self-assembly of heterostranded coiled-coil peptides. We have prepared a semiartificial Mb, named Mb-1alphaK, in which an amphiphilic and cationic alpha-helix peptide is conjugated at the heme propionate (Heme-1alphaK). Heme-1alphaK has a covalently bound iron-protoporphyrin IX (heme) at the N terminus of a 1alphaK peptide sequence. This sequence was designed to form a heterostranded coiled-coil in the presence of a counterpart amphiphilic and anionic 1alphaE peptide sequence in a parallel orientation. Two peptides, Fla(1)-1alphaE and Fla(31)-1alphaE, both incorporating a 10-methylisoalloxazine moiety as an artificial flavin molecule, were also prepared (Fla=2-[7-(10-methyl)isoalloxazinyl]-2-oxoethyl). Heme-1alphaK was successfully inserted into apomyoglobin to give Mb-1alphaK. Mb-1alphaK recognized the flavin-modified peptides and a two-alpha-helix structure was formed. In addition, an efficient ET from reduced nicotinamide adenine dinucleotide to the heme center through the flavin unit was observed. The ET rate was faster in the presence of Fla(1)-1alphaE than in the presence of Fla(31)-1alphaE or the equivalent molecule that has no peptide chain. These results demonstrate that the introduction of a functional chromophore on the Mb surface can be achieved by using specific peptide-peptide interactions. Moreover, the dependence of the ET rate on the position of the flavin indicated that the distance between the heme active site and the flavin chromophore was regulated by the three-dimensional structure of the designed polypeptide.

Amino Acid Sequence↗

PubMed2004

Ribonucleopeptides: functional RNA-peptide complexes.

Selection of functional RNAs from randomized pool of RNA molecules successfully affords RNA aptamers that specifically bind to small molecules, and that have catalytic activities. Recent structural analyses of the ribosomal RNA complex suggest that the RNA-protein complex would be a new structural candidate for the design of tailor-made receptors and enzymes. We have designed an ATP binding domain that consists of an RNA subunit and a peptide subunit by means of structure-based design approach and successive in vitro selection method. The RNA subunit is designed to consist of two functional domains; an ATP binding domain with 20 randomized nucleotides and an adjacent stem region that serves as a binding site for the RNA-binding peptide. The randomized nucleotide region was placed next to the HIV-1 Rev response element to enable the formation of "ribonucleopeptide" pools in the presence of the Rev peptide. In vitro selection of RNA oligonucleotides from the randomized pool afforded a ribonucleopeptide receptor specific for ATP. The ATP-binding ribonucleopeptide did not share the known consensus nucleotide sequence for ATP aptamers, and completely lost its ATP-binding ability in the absence of the Rev peptide. The ATP-binding activity of the ribonucleopeptide was increased by a substitution of the N-terminal amino acid of the Rev peptide. These results demonstrate that the peptide stabilizes the functional structure of RNA and suggest that amino acids outside the RNA binding region of the peptide participate in the ATP binding. Our approach would provide a new strategy for the design of tailor-made ribonucleopeptide receptors.

Adenosine Triphosphate↗

PubMed2004

Design of sensing ribonucleopeptides for small ligands.

Here we report a simple method to convert synthetic receptors to fluorescent sensors. An RNA-peptide complex (ribonucleopeptide) with a known three-dimensional structure is used as a framework of the receptor. Artificial ribonucleopeptide sensors were created with a combination of in vitro selection method and successive modification of the peptide with a fluorophore. A ribonucleopeptide complex of the fluorophore labeled peptide showed a remarkable fluorescence emission change upon binding cognate ligands.

Amines↗

PubMed2002

Pseudoalteromonas ruthenica sp. nov., isolated from marine invertebrates.

On the basis of phenotypic and genotypic characteristics and analysis of 165 rRNA sequences, a novel species belonging to the genus Pseudoalteromonas is described. Two pale-orange-pigmented strains, KMM 300T and KMM 290, isolated respectively from a mussel, Crenomytilus grayanus, and a scallop, Patinopecten yessoensis, are marine, gram-negative, aerobic, rod-shaped bacteria that produce a number of antimicrobial compounds. The strains are able to degrade gelatin, elastin, starch, DNA and Tween 80. Chitin and agar are not degraded. The isolates from marine invertebrates grew at NaCl concentrations of 1-9% and a temperature range of 10-35 degrees C and did not utilize most of the wide range of carbohydrates tested, with the exception of D-glucose, cellobiose and sucrose. The DNA G+C content was 48.4-48.9 mol%. The level of DNA homology of the two strains was 98%. DNA from the strains isolated from marine invertebrates showed 5-15% genetic relatedness to the DNA of other type strains of the genus Pseudoalteromonas. 16S rRNA analysis indicated a clear affiliation of the novel bacteria to other species of the genus. The strains are assigned to a novel species, Pseudomonas ruthenica sp. nov., with the type strain KMM 300T (= LMG 19699T = CIP 106857T).

Animals↗