Biomedical subjects

Isao Taniguchi

Publications and source records attributed to Isao Taniguchi.

12 recordsLinked to original sources

PubMed2006

Higher order structure contributes to specific differences in redox potential and electron transfer efficiency of root and leaf ferredoxins.

Plant type ferredoxin (Fd) is a small [2Fe-2S] cluster containing electron-transfer protein with a highly negative redox potential. Higher plants contain different iso-protein types of Fd in roots and leaves, reflecting the difference in redox cascades between these two tissues. We have combined subdomains of leaf and root Fds in recombinant chimeras, to examine structural effects and the relationship between groups of residues on redox potential, electron transfer, and protein-protein interactions. All chimeras had redox potentials that were intermediate to the wild type leaf and root Fds. Surprisingly, the largest differences resulted from exchange of the N-terminus, the region farthest from the redox center. Homology modeling and energy minimization calculations suggest that the N-terminal chimeras may indirectly influence redox potentials by structurally perturbing the active site. Measurements of electron transport and protein interaction indicate that synergistic interaction between the C- and N-terminal of root Fd bestows a specific high affinity for accepting electrons in the root type electron cascade, and that there is discrimination against photosynthetic electron donation to root Fd based on the C-terminus of the molecule. Taken together, the experimental and computational studies support a model in which higher order structure contributes to iso-protein specific interaction and electron-transfer properties.

Amino Acid Sequence↗

PubMed2006

Size control for two-dimensional iron oxide nanodots derived from biological molecules.

We demonstrated the fabrication of size-controlled two-dimensional iron oxide nanodots derived from the heat treatment of ferritin molecules self-immobilized on modified silicon surfaces. Ferritin molecules were immobilized onto 3-aminopropyltrimethoxysilane (3-APMS)-modified silicon surfaces by electrostatic interactions between negatively charged amino acids of ferritin molecules and amino terminal functional groups of 3-APMS. Heat treatments were performed at 400 degrees C for 60 min to fabricate two-dimensional nanodots based on ferritin cores. XPS and FT-IR results clearly indicate that ferritin shells were composed of amino acids and 3-APMS modifiers on silicon surfaces were eliminated by heat treatment. Nanodots on substrate surfaces corresponded to iron oxides. The size of nanodots was tunable in the range of 0-5 (+/-0.75) nm by in situ reactions of iron ion chelators with ferritin molecules immobilized on substrates before heat treatment.

Animals↗

PubMed2006

Formation of oriented polypeptides on Au(111) surface depends on the secondary structure controlled by peptide length.

We synthesized three different lengths of poly(L-lysine) containing an -SH group at the terminal (PLL(n)-SH, n (polymerization degree) = 4, 10, 30) and adsorbed them on an Au(111) surface. To analyze the formation process and the structure of self-assembled monolayers (SAMs), we used atomic force microscopy (AFM) and Fourier transform infrared reflection absorption spectra (FT-IR RAS). At the initial stage of SAM growth, formation of nanosize domains was confirmed by AFM imaging. The alpha-helical PLL(30)-SH exhibited a well-defined SAM structure after adsorption reached equilibrium. The alpha-helical PLL(30)-SH was almost perpendicular to the gold surface and exhibited interesting molecular packing due to the secondary structure of PLL(30)-SH and the underlying Au(111) array. The tilt angle of the helix axis from the substrate normal was estimated to be about 50 degrees (AFM) and 44 degrees (FT-IR RAS) respectively. On the other hand, PLL(4)-SH and PLL(10)-SH formed beta-sheet-type SAMs on the Au(111) surface based on the structure determined by FT-IR RAS spectrum.

Adsorption↗

PubMed2005

Direct electrochemistry of engineered cytochrome b562 molecules with a ligand binding pocket.

The rapid and reversible electron transfer reaction of cytochrome b562 was observed at an In2O3 electrode. The estimated heterogeneous electron transfer rate constant (k0') was k0' > or = 5.0 x 10(-3) cm s(-1) at pH 6.5. When the methionine-7 (Met-7) residue, which coordinates to the heme iron as an axial ligand, of the wild-type cytochrome b562 was replaced by an Ala or Gly residue, a water molecule bound to the heme iron and the electron transfer rate constants decreased to 1.3 x 10(-3) and 1.8 x 10(-3) cm s(-1), respectively. This decrease in the electron transfer rate would be due to the larger reorganization energy for the structural change at the redox site. The midpoint potential of cytochrome b562 was shifted negatively by approximately 135 mV by replacing Met-7 with Ala or Gly. Similar dissociation kinetics of cyanide for the mutated molecules as compared to native myoglobin was obtained.

Amino Acid Substitution↗

PubMed2004

Notable deuterium effect on the electron transfer rate of myoglobin.

The electron transfer reaction of wild-type myoglobin at an electrode was significantly facilitated in a D2O buffer as compared with that in an H2O buffer, with k(0)'(H2O)/k(0)'(D2O)= 0.13, while a minimal deuterium kinetic isotope effect on the myoglobin with modification at distal histidine (His-64) was observed.

Animals↗

PubMed2004

Functional evaluation of heme vinyl groups in myoglobin with symmetric protoheme isomers.

We replaced protoheme-IX in native myoglobin with the symmetric protohemes-III and -XIII, in order to investigate the role of heme vinyl-globin contacts on Mb function. The UV-visible spectra and the resonance Raman spectra in the high-frequency region (containing oxidation, spin, and coordination state marker lines) of the two reconstituted Mbs were very similar. However, the signal intensity of the Soret band in the CD spectra and the resonance Raman lines for vinyl bending modes in the low-frequency region notably differed, thereby reflecting altered heme peripheral contacts. The redox potentials, formal heterogeneous electron-transfer rates, and thermal denaturation temperatures of the two reconstituted Mbs were also indistinguishable. In addition, the oxygen binding properties of the ferrous deoxy Mbs were comparable. These results demonstrate that altered heme vinyl-globin interactions only slightly affect the physical properties of Mb. It is therefore likely that the orientation of protoheme-IX about the alpha,gamma-axis in the heme pocket is not necessarily a crucial factor for oxygen binding to native Mb.

Animals↗

PubMed2004

Growth of carbon nanotubes on a gold (111) surface using two-dimensional iron oxide nano-particle catalysts derived from iron storage protein.

We report here the preparation of two-dimensional iron oxide nano-particles from the iron storage protein ferritin immobilized on a gold surface. This paper also reports the novel finding of the lattice-oriented like growth of carbon nanotubes on a gold (111) surface using the obtained two-dimensional iron oxide nano-particles on the gold surface as a catalyst.

Journal Article↗

PubMed2003

A post genomic characterization of Arabidopsis ferredoxins.

In higher plant plastids, ferredoxin (Fd) is the unique soluble electron carrier protein located in the stroma. Consequently, a wide variety of essential metabolic and signaling processes depend upon reduction by Fd. The currently available plant genomes of Arabidopsis and rice (Oryza sativa) contain several genes encoding putative Fds, although little is known about the proteins themselves. To establish whether this variety represents redundancy or specialized function, we have recombinantly expressed and purified the four conventional [2Fe-2S] Fd proteins encoded in the Arabidopsis genome and analyzed their physical and functional properties. Two proteins are leaf type Fds, having relatively low redox potentials and supporting a higher photosynthetic activity. One protein is a root type Fd, being more efficiently reduced under nonphotosynthetic conditions and supporting a higher activity of sulfite reduction. A further Fd has a remarkably positive redox potential and so, although redox active, is limited in redox partners to which it can donate electrons. Immunological analysis indicates that all four proteins are expressed in mature leaves. This holistic view demonstrates how varied and essential soluble electron transfer functions in higher plants are fulfilled through a diversity of Fd proteins.

Amino Acid Sequence↗

PubMed2003

Detection of C-Si covalent bond in CH3 adsorbate formed by chemical reaction of CH3MgBr and H:Si(111).

High-resolution electron energy loss spectroscopy (HREELS) yielded evidence for the formation of single covalent bonds between Si(111) surface atoms and CH(3) groups from the reaction of CH(3)MgBr and hydrogen-terminated H:Si(111)(1 x 1). The vibration at 678 cm(-)(1), assigned to the C-Si bond, was isolated within the spectrum of CH(3) on deuterium-terminated D:Si(111)(1 x 1). The CH(3) groups were thermally stable at temperatures below 600 K. The C-Si bonds are essential for enhancing the usefulness of alkyl moieties, which will lead to a new prospective technology of nanoscale fabrication and biochemical application.

Methane↗

PubMed2003

Comparison of nanotube structures constructed from alpha-, beta-, and gamma-cyclodextrins by potential-controlled adsorption.

"Nanotube" structures of the alpha-, beta-, and gamma-cyclodextrins (CyD's), which are similar to that of CyD-polyrotaxane, were constructed by potential-controlled adsorption onto Au(111) surfaces in sodium perchlorate solution without a threaded polymer. CyD molecules adsorbed randomly on bare Au(111) surfaces without potential control and the desorption of CyD's from Au surfaces was observed at a negative potential of less than -0.60 V versus SCE. On the other hand, in the specific range between these potentials, ordered molecular arrays with "nanotube" structures of the CyD's (alpha-, beta-, and gamma-CyD) were observed on Au(111). The range of potentials for formation of the "nanotube" structures of alpha-, beta-, and gamma-CyD was from -0.15 to -0.20 V, from -0.25 to -0.45 V, and from -0.22 to -0.45 V, respectively. beta- and gamma-CyD require a more negative potential for adsorption-induced self-organization (AISO) than alpha-CyD in order to weaken adsorption and induce self-organization. Furthermore, we have succeeded in the visualization of the dynamic process in solution, such as the self-ordering, and the destruction of the nanotube structure. These results indicate that control of the electrode potential facilitates management of the delicate balance of various interactions, resulting in the formation of two-dimensional supramolecular structures on the substrates.

Journal Article↗

PubMed1999

New Robust Bleomycin Analogues: Synthesis, Spectroscopy, and Crystal Structures of the Copper(II) Complexes.

Two new bleomycin analogues, 2-[((2-(4-imidazolyl)ethyl)amino)carbonyl]-6-[((2-amino-2-methylpropyl)amino)methyl]pyridine = L(3)() and 2-[((2-(4-imidazolyl)ethyl)amino)carbonyl]-6-[((2-amino-1,1,2-trimethylpropyl)amino)methyl]pyridine = L(4)(), were synthesized in order to create air-stable ligands of their Cu(I) (and Fe(II)) complexes. The protonation constants (log K(n)()) of the ligands at 25 degrees C and I = 0.1 M NaNO(3) were 9.9, 6.9, and 5.2 for L(3)() and 10.0, 6.7, and 3.9 for L(4)(). The complexation of the triprotonated L(3)() and L(4)() with Cu(II) started at pH < 5 to yield 4-coordinate [Cu(II)(H(-)(1)L).H(+)](2+) complexes, 4 and 6, respectively, followed by formation of square-pyramidal [Cu(II)(H(-)(1)L)](+) complexes, 5 and 7, with pK(a) values of 5.6 for 5 and 5.9 for 7. The complexation constants, log K(Cu)()II(H)()-1(L), were 8.9 for [Cu(II)(H(-)(1)L(3))](+), 5, and 8.6 for [Cu(II)(H(-)(1)L(4))](+), 7, respectively. The structures of [Cu(II)(H(-)(1)L(3))]ClO(4) (5.ClO(4)) and [Cu(II)(H(-)(1)L(4))]BF(4) (7.BF(4)) were determined by X-ray crystallography. Crystal data for 5.ClO(4): monoclinic, space group P2(1)/n (No. 14), a = 13.978(6) Å, b = 8.103(3) Å, c = 18.037(5) Å, beta = 98.61(3) degrees, V = 2019(1) Å(3), Z = 4, R = 0.053, and R(w) = 0.044 for 2996 [I > 3sigma(I)] reflections. Crystal data for 7.BF(4): monoclinic, space group P2(1)/n (No. 14), a = 16.092 (4) Å, b = 7.974(4) Å, c = 16.819(2) Å, beta = 99.64(1) degrees, V = 2127(1) Å(3), Z = 4, R = 0.040, and R(w) = 0.025 for 1633 [I > 4sigma(I)] reflections. The coordination geometry around the copper was a distorted square-pyramid in 5, while that of 7 was the intermediate between a trigonal-bipyramid and a square-pyramid. The distortion is influenced strongly by the number of the methyl group. The EPR spectral data for both copper(II) complexes were consistent with the retention of the solid-state structure in frozen DMF/MeOH (1:1) solution at 77 K. The visible absorption spectra of 10% DMF/aqueous solutions (pH 9.5) of 5 and 7 at I = 0.1 M NaNO(3) showed absorption maxima at 646 nm with a shoulder at ca. 900 nm for 5 and at 658 and 888 nm for 7. The red-shift of 7 by ca. 12 nm relative to 5 reflects the distortion toward the trigonal-bipyramidal geometry of 7 in solution. Both complexes displayed irreversible redox behavior in DMF at I = 0.1 M tetra(n-butyl)ammonium tetrafluoroborate. The anodic and cathodic peak potentials obtained by cyclic voltammetry for 5 and 7 were -0.14 and -0.76 V for 5 and -0.17 and -0.80 for 7 vs Ag/AgCl. The cathodic potentials of copper(II) complexes were shifted toward the anodic direction by ca. 20-60 mV compared to the nonsubstituted 5-coordinate, [Cu(II)(H(-)(1)L(1))](+) complex, 16 (-0.82 V vs Ag/AgCl). The Cu(I) complexes (9and 10) are air-oxidized to the corresponding Cu(II) complexes, 5 and 7, respectively.

Journal Article↗

PubMed1996

Oxo-Centered Mixed-Ligand Triruthenium Complexes Having Redox-Active N-Methyl-4,4'-bipyridinium Ions (mbpy(+)). Reversible Multistep Electrochemical Properties of [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](2+) and [Ru(III)(3)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(L)](3+) (L = H(2)O and N-Heterocyclic Ligands).

A new series of oxo-centered acetate-bridged triruthenium comlexes having two redox-active N-methyl-4,4'-bipyridinium ions (mbpy(+)) have been prepared, and their reversible multistep and multielectron electrochemical properties are reported: [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](2+) and [Ru(III)(3)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(L)](3+) (L = H(2)O, pyrazine (pz), pyridine (py), imidazole (Him), and 4-(dimethylamino)pyridine (dmap)). Among these series, the CO complex, [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](ClO(4))(2).2DMF (1b.2DMF) was structurally characterized by X-ray crystallography. 1b.2DMF crystallizes in the monoclinic space group P2(1)/m (No. 11) with a = 8.740(6) Å, b = 32.269(6) Å, c = 10.276(4) Å, beta = 103.37(5) degrees, V = 2820(2) Å(3), Z = 2, d(calcd) = 1.636 g cm(-)(3), and R = 0.071 (R(w) = 0.074) for 5277 independent reflections (|F(o)| > 3sigma(|F(o)|). The (CO)Ru.Ru distance (3.410(2) Å) is appreciably longer than the other Ru.Ru distance (3.276(2) Å), indicating that the trinuclear core is in the valence-trapped Ru(III)(2)Ru(II)(CO) oxidation state. The cyclic voltammogram of [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](PF(6))(2) (1a) shows a total of seven reversible one-electron redox steps at E(1/2) = +0.90, +0.26, -1.07, -1.17, -1.56, -1.97, and -2.32 V and one irreversible step at E(pc) = -2.99 V vs Fc/Fc(+) in a 0.1 M [(n-C(4)H(9))(4)N]PF(6)-CH(3)CN solution (M = mol dm(-)(3)). All of the waves are clearly assignable to the triruthenium "Ru(3)(&mgr;(3)-O)" core-based or mbpy(+) ligand-based processes. The splitting of each ligand-based redox processes (mbpy(+)/mbpy(*) and mbpy(*)/mbpy(-)) into two one-electron steps indicates that electronic interactions between two terminal ligands occur through the triruthenium cluster core. Other mixed-ligand Ru(III)(3) analogs also show multistep redox behavior involving a total of eight or nine electrons. While the extent of interactions between ligands is much smaller than that found in the CO complex, it is systematically changed by the nature of L; with more basic L, interactions between two mbpy(+) ligands become larger.

Journal Article↗