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Biomedical subjects

K Takamiya

Publications and source records attributed to K Takamiya.

At least 109 records · Page 6Linked to original sources
PubMed1988

The effect of kazusamycin B on the cell cycle and morphology of cultured L1210 cells.

The effect of a potent antitumor antibiotic, kazusamycin B, on the cell cycle of L1210 cells was examined. Kazusamycin B arrested synchronized L1210 cells at G1 phase. Retardation of metaphase initiation was also observed. Flow cytometric analysis of kazusamycin B-treated asynchronized cells also confirmed G1 arresting effect of kazusamycin B. In addition, an unidentified cell population with lower fluorescence intensity than G1 population was observed when the cells were exposed to the drug longer than 12 hours. Morphology of kazusamycin B-treated L1210 cells revealed that the intranuclear structure changed within 4 hours, and that abnormal condensation of nuclei coincided with the appearance of unidentified population. Kazusamycin B inhibited RNA synthesis moderately but specifically at 2 hours. However, this inhibition might be a secondary effect of the antibiotic-induced structural abnormality of the nuclei.

Animals↗
PubMed1988

Anti-tumor effect of dithiole compounds.

A series of dithiole compounds, N-(1,3-dithiole-2-ylidene)-N,N-dialkyl-ammonium salts, was synthesized and tested for anti-tumor activity. Most of them exhibited a potent cytotoxic activity against cultured cells at IC50 concentrations less than 1 micrograms/ml. They were also effective in increasing the life-span of mice bearing L1210 leukemic cells. Their anti-tumor activities both in vitro and in vivo were related to the length of alkyl chain moieties, among which EX-015, having n-decyl chains, was found to be most effective in vivo; EX-015 prolonged the survival time of mice implanted with L1210 cells by 69% when given once daily for 5 days at 0.8 mg/kg. In addition, EX-015 inhibited the RNA and protein syntheses of L1210 cells, but less so with the DNA synthesis.

Animals↗
PubMed1987

Complete amino acid sequence of cytochrome c551 from Erythrobacter species strain OCh 114.

The complete amino acid sequence of cytochrome c551 isolated from an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh 114, was determined. The cytochrome molecule was composed of a total of 119 amino acid residues and its molecular weight including heme was calculated to be 13,235. The sequence was (Sequence: see text). Its molecular weight indicates that this cytochrome is of the L-type. Sequence alignment with other bacterial cytochromes c shows that this cytochrome is similar to cytochromes c of Rhodobacter capsulatus, Rhodobacter sphaeroides, and Paracoccus denitrificans, which were grouped into the alpha-3 subcluster from the 16S rRNA sequence analysis.

Amino Acid Sequence↗
PubMed1987

Structural gene of cytochrome b-562 from the cytochrome b-c1 complex of Rhodobacter sphaeroides.

The structural gene coding for cytochrome b-562 isolated from the cytochrome b-c1 complex of Rhodobacter (Rhodopseudomonas) sphaeroides has been cloned. Its nucleotide sequence has been determined and the amino acid sequence was deduced therefrom. It consists of 157 amino acids (Mr 17,237) and contains four hydrophobic segments. The first 30 residues in the predicted amino acid sequence are the same as those determined for the NH2-terminal portion of purified cytochrome b-562. The amino acid composition is in accord with that determined for the pure protein. From the hydropathy profile and molar ratio of protoheme to cytochrome b-562, it is suggested that the structural and functional unit of the cytochrome is a two-heme cross-linked homodimer.

Amino Acid Sequence↗
PubMed1987

Antitumor effect of kazusamycin B on experimental tumors.

Kazusamycin B, a novel antibiotic (MW 542) isolated from fermentation broth of Streptomyces sp. No. 81-484 showed a broad antitumor spectrum both in vitro and in vivo. IC50 against the growth of tumor cells was around 1 ng/ml at 72 hours-exposure in vitro. Intraperitoneal injection of the antibiotic was effective in inhibiting the growth of murine tumors, S180, P388, EL-4, and B16. It was also active against doxorubicin-resistant P388, hepatic metastases of L5178Y-ML, pulmonary metastases of 3LL, and human mammary cancer MX-1 xenografted to nude mice. However, the activity of kazusamycin B toward L1210 or human lung cancer LX-1 was weaker. According to the results of comparative studies on the effect of kazusamycins B and A, an analog of B, there seemed to be no significant difference in their effectiveness. The effective dose range and toxicity were markedly dependent on tumor lines tested and the regimen used. Maximum tolerated dose in mice with subcutaneous tumors was much higher than that in mice bearing ascitic leukemia as P388. Although intermittent administration could greatly reduce the cumulative toxicity of the drug, therapeutic effect was similar with both successive and intermittent administration schedules.

Animals↗
PubMed1986

A new membrane-bound b-type cytochrome, cytochrome b-558, from photosynthetically grown Rhodopseudomonas sphaeroides.

A new membrane-bound b-type cytochrome, cytochrome b-558, was removed from chromatophore membranes of photosynthetically grown Rhodopseudomonas sphaeroides strain R-26 by deoxycholate-cholate extraction. The cytochrome was purified by ammonium sulfate fractionation and ion-exchange chromatography. Cytochrome b-558 had absorption maxima at 280 and 405 nm in the oxidized form, and at 558, 528, and 420 nm in the reduced form. It had a midpoint potential of--130 mV at pH 7.0. The minimal molecular weight of this protein was 42,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it contained one mole heme per mole of protein. The isoelectric point was 8.5. The electrophoretic pattern of heme-carrying proteins and the redox potentiometry showed that cytochrome b-558 was present in membranes from wild type, strain R-26, and strain GA grown photosynthetically, but not from any strain grown aerobically.

Amino Acids↗
PubMed1986

Characterization by EPR spectroscopy of cytochrome b-562 isolated from the cytochrome b-c1 complex of Rhodopseudomonas sphaeroides R-26.

The EPR spectra of cytochrome b-562 isolated from the cytochrome b-c1 complex of Rhodopseudomonas sphaeroides were measured at liquid helium temperature. The purified cytochrome b-562 gives a high spin signal at g = 6.0. Anaerobic titration of this signal confirmed the presence of two redox components with Em = 40 and -110 mV at pH 7.5. These values are consistent with the published ones, Em = 55 and -100 mV at pH 7.0, that were optically estimated for the same type of preparation (Iba et al. (1985) FEBS Lett. 183, 151-154). The power saturation behavior of the g = 6.0 signal at different redox potentials indicated a direct spin-spin interaction between these two redox centers.

Cytochrome b Group↗
PubMed1986

Photophosphorylation and oxidative phosphorylation in intact cells and chromatophores of an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114.

Light-induced ATP synthesis was studied in intact cells and chromatophores of Erythrobacter sp. strain OCh114. ATP synthesis was measured by both the pH method and the luciferin-luciferase luminescence method. The rate of ATP synthesis was moderate (a typical value of 0.65 mol of ATP per mol of bacteriochlorophyll per min), and synthesis was inhibited by antimycin A. ATP was synthesized under illumination only under aerobic conditions and not under anaerobic conditions. This characteristic was similar to that of other light-induced energy transduction processes in this bacterial species, such as oxidation of reaction center, oxidation of cytochrome c551, and translocation of H+, which were not observed under anaerobic conditions. This phenomenon was reconciled with the fact that the Erythrobacter sp. could not grow anaerobically even in the light. The characteristics of oxidative phosphorylation and ATP hydrolysis were also investigated. The respiratory ratio of chromatophores was 2.3. Typical rates of oxidative phosphorylation by NADH and by succinate were 2.9 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.22) and 1.1 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.19), respectively. A typical rate of ATP hydrolysis was 0.25 mol of ATP per mol of bacteriochlorophyll per min in chromatophores. ATPase and adenylate kinase are also involved in the metabolism of adenine nucleotides in this bacterium.

Adenosine Triphosphate↗
PubMed1984

Transmembrane orientation of reaction centers in proteoliposomes from Rhodopseudomonas sphaeroides.

The photochemical reaction centers from Rhodopseudomonas sphaeroides were reconstituted with soybean phospholipids into liposomes by the cholate-dialysis method. The transmembrane orientation of the reaction centers in the proteoliposomes and the morphology of the vesicles were investigated. The orientation was determined by the reduction of externally added cytochrome c after its photooxidation by a flash. The structure of the vesicles was examined by electron microscope. Discontinuous sucrose density gradient centrifugation yielded several proteoliposome fractions with different vesicular sizes and reaction-center orientations. The proportion of the reaction centers that exposed their cytochrome c reacting sites to the outside of the vesicles increased from 45 to 85% with an increase of the vesicular size. The proportion also depended on the ionic composition of the dialysis buffer. The optimal ionic environment during the dialysis (100 mM NaCl or 2.5 mM MgSO4) gave a liposome yield of 25-30% with a highly asymmetric orientation (greater than 60%). Entrapping of cytochrome c molecules into the phospholipid vesicles had little effect on the orientation of the reaction centers.

Bacterial Proteins↗
PubMed1983

Inhibitory effect of N,N'-dicyclohexylcarbodiimide (DCCD) on the electron transfer involving cytochrome b-c2 oxidoreductase in Rhodopseudomonas sphaeroides.

N,N'-Dicyclohexylcarbodiimide (DCCD) inhibited dark re-reduction of cytochrome c2 and reduction of b-type cytochrome, both of which are closely associated with electron transfer involving a cytochrome b-c2 oxidoreductase, after a single-turnover flash excitation in the chromatophore membranes from a photosynthetic bacterium, Rhodopseudomonas sphaeroides. Rapid proton uptakes (HI+, HII+) and the formation of the membrane potential registered by carotenoid bandshift phase III were also inhibited by DCCD. The electron transfer was inhibited in the presence of either valinomycin or carbonylcyanide-m-chlorophenylhydrazone (CCCP). These results indicated that DCCD inhibited the electron transfer involving the cytochrome b-c2 oxidoreductase in the bacterium. The inhibition was irreversible. A hydrophilic carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC), did not affect the above-mentioned reactions. Thus, DCCD may interact with the hydrophobic region(s) in the chromatophore membranes from photosynthetic bacteria resulting in the inhibition(s) of the photosynthetic cyclic electron transfer.

Carbodiimides↗
PubMed1982

Characterization of electron donation to cytochrome c-555 in Chromatium vinosum from ferrocyanide, tetramethylphenylenediamine and reduced dimethylquinone. Effects of redox potential, pH and salt concentration.

1. The dependences of the reduction of ferricytochrome c-555 in the reaction center-cytochrome c complex on the redox potential and pH were investigated using N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), ferrocyanide, and reduced 2,5-dimethyl-p-quinone as electron donors. 2. In the reduction of cytochrome c-555 by TMPD, the unprotonated form was the exclusive electron donor to the cytochrome with a second-order rate constant of 1.0 X 10(5) M-1.s-1. 3. Ferrocyanide reduced cytochrome c-555 slowly with a rate constant of 7.8 X 10(3) M-1.s-1 at infinite salt concentration. The value of -5.2 X 10(-4) elementary charge/A2 was estimated as the surface charge density in the vicinity of cytochrome c-555 by analyzing the salt effect on the cytochrome reduction using the Gouy-Chapman theory. 4. The characteristics of the dependences of the reduction of cytochrome c-555 by reduced 2,5-dimethyl-p-quinone on the redox potential and pH were well explained by the redox potential and pH dependences of the formation of the semiquinone. In the neutral-to-alkaline pH range the anionic semiquinone was the main electron-donating species with a second-order rate constant of 6.0 X 10(7) m-1.s-1.

Bacterial Chromatophores↗
PubMed1980

Effects of surface potential on the equilibrium and kinetics of redox reactions of membrane components with external reagents in chromatophores from Rhodopseudomonas sphaeroides.

The characteristics of the salt and pH dependences of the redox levels of cytochrome c2 and reaction center bacteriochlorophyll were studied in chromatophores from Rhodopseudomonas sphaeroides. They could be explained in terms of the difference of redox potential in the membrane from that in the bulk aqueous phase due to the electrostatic potential difference arising from charges fixed on the membrane surface. The midpoint potentials (Em) became lower when the surface potential (the electrostatic potential at the surface with reference to the bulk aqueous phase) had large negative values at lower salt concentrations at neutral pH, as predicted by the Gouy-Chapman theory. The rate of oxidation of cytochrome c2 in chromatophores by ferricyanide also depended on salt and pH levels. The rate was low at low salt concentrations, probably because of the lower surface concentration of ferricyanide compared with the bulk concentration, due to the surface potential.

Bacterial Chromatophores↗
PubMed1979

The recognition of a special ubiquinone functionally central in the ubiquinone-cytochrome b-c2 oxidoreductase.

Although the energy conserving membranes of the photosynthetic bacterium Rhodopseudomonas sphaeroides contain a 25 (+/- 3)-fold molar excess of ubiquinone over the photochemical reaction center, the activity of the ubiquinone-cytochrome b-c2 oxidoreductase is unaffected by quinone extraction until only 3, or at most 4, ubiquinones remain; only then does further extraction prevent the function of the oxidoreductase. Since 2 of these last ubiquinones are integral parts of the photochemical reaction center, we conclude that the ubiquinone-cytochrome b-c2 oxidoreductase requires only 1, or at most 2, molecules of ubiquinone-10 for its function. Earlier kinetic data identified a major electron donor to ferricytochrome c2 as a single molecule (known as Z) which requires 2 electrons and 2 protons for its equilibrium reduction. Hence, we identify a single molecule of quinone, probably ubiquinone-10 in a special environment, as a major electron donor to ferricytochrome c2 in the ubiquinone cytochrome b-c2 oxidoreductase.

Cytochrome c Group↗