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Biomedical subjects

M Kobayashi

Publications and source records attributed to M Kobayashi.

At least 415 records · Page 23Linked to original sources
PubMed2000

Crystal structures of photosynthetic reaction center and high-potential iron-sulfur protein from Thermochromatium tepidum: thermostability and electron transfer.

The reaction center (RC) of photosynthetic bacteria is a membrane protein complex that promotes a light-induced charge separation during the primary process of photosynthesis. In the photosynthetic electron transfer chain, the soluble electron carrier proteins transport electrons to the RC and reduce the photo-oxidized special-pair of bacteriochlorophyll. The high-potential iron-sulfur protein (HiPIP) is known to serve as an electron donor to the RC in some species, where the c-type cytochrome subunit, the peripheral subunit of the RC, directly accepts electrons from the HiPIP. Here we report the crystal structures of the RC and the HiPIP from Thermochromatium (Tch.) tepidum, at 2.2-A and 1.5-A resolution, respectively. Tch. tepidum can grow at the highest temperature of all known purple bacteria, and the Tch. tepidum RC shows some degree of stability to high temperature. Comparison with the RCs of mesophiles, such as Blastochloris viridis, has shown that the Tch. tepidum RC possesses more Arg residues at the membrane surface, which might contribute to the stability of this membrane protein. The RC and the HiPIP both possess hydrophobic patches on their respective surfaces, and the HiPIP is expected to interact with the cytochrome subunit by hydrophobic interactions near the heme-1, the most distal heme to the special-pair.

Chromatiaceae↗
PubMed2000

New multidrug resistance modulators from Atractylodis Lanceae Rhizoma.

Three new oligoacylated sucroses designated atractysucroses-I, -II, and -III were obtained from Atractylodis Lanceae Rhizoma as multidrug resistance (MDR) modulating substances against human carcinoma cell lines and their chemical structures were characterized as a mixture of acyl groups. Atractysucrose-I modulates MDR in KB-C2 cells as strongly as verapamil. This is the first example of an MDR-modulator classified as a carbohydrate.

Asteraceae↗
PubMed2000

Measurement of direct photon emission in K+-->pi(+)pi(0)gamma decay

We have performed a measurement of the K+-->pi(+)pi(0)gamma decay and have observed 2x10(4) events. The best fit to the decay spectrum gives a branching ratio for direct photon emission of (4.7+/-0.8+/-0. 3)x10(-6) in the pi(+) kinetic energy region of 55 to 90 MeV and requires no component due to interference with inner bremsstrahlung.

Journal Article↗
PubMed2000

The chitinase gene of the silkworm, Bombyx mori, contains a novel Tc-like transposable element.

We have determined the cDNA sequence and the genomic organization of the chitinase gene of the silkworm, Bombyx mori. The cDNA encodes 544 amino acids having 83% amino acid homology to the chitinase of the tobacoo hornworm, Manduca sexta. The total length of the gene is larger than 25 kilobase pairs, and it is separated into 11 exons. The intron-exon boundaries are all in accordance with the GT-AG rule. Also, the TATA box sequence was found in the 5' upstream region of the gene, and the gene is mapped on the seventh chromosome. A novel DNA type transposon that shows similarity to the Tc-like element was found in the third intron in some strains of B. mori; other strains, however, lack this element in the same intron. This element has long terminal inverted repeats, presumably encodes a transposase of about 340 amino acids with a DDE motif, and has an amino-terminal domain with a strong nuclear localization function. Seven other transposable elements with homologous but distinct sequences were isolated from the B. mori genome. Together with plaque hybridization results, our findings suggest that these novel elements exist in multiple copies constituting a new Tc-like transposable element family in the silkworm genome.

Amino Acid Sequence↗
PubMed2000

[Occupational contact dermatitis in women].

In work in which women predominate, the highest rate of the occupational contact dermatitis is seen among hairdressers and medical nursing staffs. Twelve such cases are presented and several points regarding the diagnosis and treatments are discussed. The patients were five hairdressers, two dental technicians, two nurses and three woman divers. A patch test was useful in identifying the allergens or irritants in most cases.

Adolescent↗
PubMed2000

The dimerization of folded monomers of ribulose 1,5-bisphosphate carboxylase/oxygenase.

Spontaneous refolding and reconstitution processes of dimeric ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) from Rhodospirillum rubrum have been investigated using size-exclusion high performance liquid chromatography (HPLC), spectroscopic, and activity measurements. When the unfolded Rubisco in guanidine hydrochloride is diluted at 4 degrees C, a folding intermediate (Rubisco-I) is rapidly formed, which remains in an unstable monomeric state and gradually develops into folded monomer (Rubisco-M) at 4 degrees C but undergoes irreversible aggregation at 25 degrees C. Refolding of Rubisco-I to Rubisco-M is a very slow process, taking about 20 h for 70% conversion at 4 degrees C. Rubisco-M is stable at 4 degrees C and is capable of forming an active dimer spontaneously when incubated at a temperature higher than 10 degrees C. The dynamic dimerization process has been measured in a temperature range of 4-35 degrees C by HPLC, and the results demonstrate that the dimerization is strongly facilitated by the temperature. It is found that dithiothreitol is essential for the spontaneous reconstitution of Rubisco.

Chromatography, High Pressure Liquid↗
PubMed2000

Neurotrophic function of conditioned medium from human amniotic epithelial cells.

Human amniotic epithelial cells (HAEC) may have pluripotent function because they are formed from the epiblast cells at the 8th day of fertilization. Previously, we reported that HAEC have the capacity to synthesize and release acetylcholine and catecholamine associated with the binding sites of catecholamine receptors. We show the neurotrophic function of a conditioned medium from HAEC using cultured cortical neurons of E18 rats. Extensive analyses with various techniques demonstrated that HAEC and immortalized HAEC synthesize and release brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and nerve growth factor (NGF). Other neurotrophic factors were not detected in a cultured medium of HAEC by enzyme immunoassay. Various neurotrophic factors or growth factors did not show neurotrophic effects on E18 rat neuron except for EGF. Because EGF was not detected in the conditioned medium of HAEC, these data indicate an unidentified neurotrophic factor presently that is synthesized and released from HAEC. The amniotic membrane may have a significant role in supplying neurotrophic factors to the amniotic fluid as well as neurotransmitters, suggesting an important function to the early stages of neural development in the embryo.

Amniotic Fluid↗
PubMed2000

Rice dwarf mutant d1, which is defective in the alpha subunit of the heterotrimeric G protein, affects gibberellin signal transduction.

Previously, we reported that the rice dwarf mutant, d1, is defective in the alpha subunit of the heterotrimeric G protein (Galpha). In the present study, gibberellin (GA) signaling in d1 and the role of the Galpha protein in the GA-signaling pathway were investigated. Compared with the wild type, GA induction of alpha-amylase activity in aleurone cells of d1 was greatly reduced. Relative to the wild type, the GA(3)-treated aleurone layer of d1 had lower expression of Ramy1A, which encodes alpha-amylase, and OsGAMYB, which encodes a GA-inducible transcriptional factor, and no increase in expression of Ca(2 +)-ATPase. However, in the presence of high GA concentrations, alpha-amylase induction occurred even in d1. The GA sensitivity of second leaf sheath elongation in d1 was similar to that of the wild type in terms of dose responsiveness, but the response of internode elongation to GA was much lower in d1. Furthermore, Os20ox expression was up-regulated, and the GA content was elevated in the stunted internodes of d1. All these results suggest that d1 affects a part of the GA-signaling pathway, namely the induction of alpha-amylase in the aleurone layer and internode elongation. In addition, a double mutant between d1 and another GA-signaling mutant, slr, revealed that SLR is epistatic to the D1, supporting that the Galpha protein is involved in GA signaling. However, the data also provide evidence for the presence of an alternative GA-signaling pathway that does not involve the Galpha protein. It is proposed that GA signaling via the Galpha protein may be more sensitive than that of the alternative pathway, as indicated by the low GA responsiveness of this Galpha-independent pathway.

Epistasis, Genetic↗
PubMed2000

A pathogenic role of Th2 responses on the severity of encephalomyelitis induced in mice by herpes simplex virus type 2 infection.

A pathogenic role of Th2 cells and their cytokine products (IL-4 and IL-10, Th2 cytokines) on the development of herpes simplex myelitis (HSM) was studied in mice exposed to footpad injection of herpes simplex virus type 2 (HSV-2). Morbidity and mortality of mice with HSM (HSM mice) increased when they were treated with a mixture of Th2 cytokines. Additionally, survival rates of HSM mice increased when they were treated with a mixture of mAbs for Th2 cytokines. As compared with HSM mice treated with saline, the growth of HSV-2 in spinal cords of HSM mice treated with the mixture of Th2 cytokines increased. Th2 cells (myelitis-associated Th2 cells, MTh2 cells) were demonstrated among cerebrospinal fluid cells from HSM mice. After the stimulation with HSV-2 antigen (Ag), MTh2 cells from HSM mice previously treated with the mixture of Th2 cytokines produced enhanced amounts of Th2 cytokines into their culture fluids, as compared with the amount of Th2 cytokines produced by MTh2 cells. Th2 cells were also demonstrated in mononuclear cells from spleens of HSM mice. When compared with HSM mice inoculated with splenic CD4(+) T cells from normal mice, morbidity and mortality of HSM mice inoculated with MTh2 cells markedly increased. These results indicated that the severity of HSM induced in mice by footpad injection of HSV-2 was influenced by MTh2 cells or Th2 cytokines released from these MTh2 cells. Th2 responses manifested in mice by HSV-2 infection may act as a pathogenic enhancer of HSM severities.

Adoptive Transfer↗
PubMed2000

Measurement of structure-dependent K+ --> &mgr;(+)nu(&mgr;)gamma decay

We report the first measurement of a structure-dependent component in the decay K+-->&mgr;(+)nu(&mgr;)gamma. Using the kinematic region where the muon kinetic energy is greater than 137 MeV and the photon energy is greater than 90 MeV, we find that the absolute value of the sum of the vector and axial-vector form factors is |F(V)+F(A)| = 0.165+/-0.007+/-0.011. This corresponds to a branching ratio of B(SD+) = (1.33+/-0.12+/-0.18)x10(-5). We also set the limit -0. 04<F(V)-F(A)<0.24 at 90% C.L.

Journal Article↗
PubMed2000

Preparation of enteric coated timed-release press-coated tablets and evaluation of their function by in vitro and in vivo tests for colon targeting.

As a new oral drug delivery system for colon targeting, enteric coated timed-release press-coated tablets (ETP tablets) were developed by coating enteric polymer on timed-release press-coated tablets composed of an outer shell of hydroxypropylcellulose and core tablet containing diltiazem hydrochloride (DIL) as a model drug. The results of the in vitro dissolution tests in JP 1st fluid (pH 1.2) and JP 2nd fluid (pH 6.8) indicated that these tablets showed both acid resistance and timed-release. To clarify whether ETP tablets could have been of use in the gastrointestinal tract, ETP tablets with a layer of phenylpropanolamine hydrochloride (PPA) (a marker of gastric emptying) between the enteric coating layer and outer shell were prepared, and were administered to beagle dogs. The gastric emptying time and lag time after gastric emptying were evaluated by determining the times at which PPA and DIL first appeared in the plasma (TFA(PPA) and TFA(DIL), respectively). TFA(PPA) and TFA(DIL) were about 4 and 7 h, respectively. This value of TFA(PPA) indicated that ETP tablets displayed acid resistance in the stomach as well as in JP Ist fluid. Subtraction of TFA(PPA) from TFA(DIL) gave a value of about 3 h which agreed well with the lag time determined by in vitro dissolution test in JP 2nd fluid. Also, the results seemed to be in accordance with the time at which the tablets reached the colon after gastric emptying. Therefore, ETP tablets seemed to be an effective tool for oral site-specific delivery including targeting of the colon.

Administration, Oral↗
PubMed2000

Synthesis and biological property of carba and 20-deoxo analogues of arenastatin A.

The carba analogue, in which a methylene group is substituted for the oxygen atom linked to C-15, and 20-deoxo analogue of arenastatin A, a potent cytotoxic spongean depsipeptide, were synthesized. Both analogues lacking the 15,20-ester function, which was easily metabolized in serum, showed good stability in serum as well as moderate cytotoxic activity against KB cells and better solubility.

Animals↗
PubMed2000

Retinoblastoma protein phosphorylation via PI 3-kinase and mTOR pathway regulates adipocyte differentiation.

In the early phase of adipocyte differentiation, transient increase of DNA synthesis, called clonal expansion, and transient hyperphosphorylation of retinoblastoma protein (Rb) are observed. We investigated the role of these phenomena in insulin-induced adipocyte differentiation of 3T3-L1 cells. Insulin-induced clonal expansion, Rb phosphorylation and adipocyte differentiation were all inhibited by the PI 3-kinase inhibitors and rapamycin, but not the MEK inhibitor, whereas the MEK inhibitor, but not PI 3-kinase inhibitors or rapamycin, decreased c-fos induction. We conclude that insulin induces hyperphosphorylation of Rb via PI 3-kinase and mTOR dependent pathway, which promotes clonal expansion and adipocyte differentiation of 3T3-L1 cells.

1-Methyl-3-isobutylxanthine↗
PubMed2000

Solution structure of monomeric peptide YY supports the functional significance of the PP-fold.

Peptide YY (PYY) belongs to a family of peptides including neuropeptide Y (NPY) and pancreatic peptide (PP) that regulate numerous functions through both central and peripheral receptors. The solution structure of these peptides is hypothesized to be critically important in receptor selectivity and activation, based on prior demonstration of a stable tertiary conformation of PP called the "PP-fold". Circular dichroism (CD) spectra show a pH-dependent structural transition in the pH range 3-4. Thus we describe the tertiary structure of porcine PYY in water at pH 5.5, 25 degrees C, and 150 mM NaCl, as determined from 2D (1)H NMR data recorded at 500 MHz. A constraint set consisting of 396 interproton distances from NOE data was used as input for distance geometry, simulated annealing, and restrained energy minimization calculations in X-PLOR. The RMSDs of the 20 X-PLOR-generated structures were 0.71 +/- 0.14 and 1.16 +/- 0.17 A, respectively, for backbone and heavy atom overlays of residues 1-34. The resulting structure consists of two C-terminal helical segments from residues 17 to 22 and 25 to 33 separated by a kink at residues 23, 24, and 25, a turn centered around residues 12-14, and the N-terminus folded near residues 30 and 31. The well-defined portions of the PYY structure reported here bear a marked similarity to the structure of PP. Our findings strongly support the importance of the stable folded structure of this family of peptides for binding and activation of Y receptor subtypes.

Amino Acid Sequence↗
PubMed2000

Studies on applicability of press-coated tablets using hydroxypropylcellulose (HPC) in the outer shell for timed-release preparations.

Press-coated tablets, containing diltiazem hydrochloride (DIL) in the core tablet and coated with hydroxypropylcellulose (HPC) as the outer shell, were examined for applicability as timed-release tablets with a predetermined lag time and subsequent rapid drug release phase. Various types of press-coated tablets were prepared using a rotary tabletting machine and their DIL dissolution behavior was evaluated by the JP paddle method. The results indicated that tablets with the timed-release function could be prepared, and that the lag times were prolonged as the viscosity of HPC and the amount of the outer shell were increased. The lag times could be controlled widely by the above method, however, the compression load had little effect. Two different kinds of timed-release press-coated tablets that showed lag times of 3 and 6 h in the in vitro test (denoted PCT(L3) and PCT(L6), respectively) were administered to beagle dogs. DIL was first detected in the plasma more than 3 h after administration, and both tablets showed timed-release. The lag times showed a good agreement between the in vivo and in vitro tests in PCT(L3). However, the in vivo lag times were about 4 h in PCT(L6) and were much shorter than the in vitro lag time. The dissolution test was performed at different paddle rotation speeds, and good agreement was obtained between the in vivo and in vitro lag times at 150 rpm. This suggested that the effects of gastrointestinal peristalsis and contraction should also be taken into consideration for the further development of drug delivery systems.

Animals↗
PubMed2000

Enhancement of sympathetic neuron survival by synergistic action of NT3 and GDNF.

Although roles of neurotrophin-3 (NT3) and glial cell line-derived neurotrophic factor (GDNF) are suggested for sympathetic neuron development, survival activity of either NT3 or GDNF alone on cultured embryonic rat sympathetic neurons is low (10-20%). We demonstrate that a combination of both NT3 and GDNF exerts a remarkable survival activity (85%). NT3 and GDNF did not affect expression levels of their receptors. However, stimulation with both NT3 and GDNF caused tyrosine-phosphorylation of Ret/GDNF-receptor at a level higher than that caused by GDNF alone. Furthermore, stimulation with both GDNF and NT3 induced an enhanced Thr308-phosphorylation of Akt kinase. These results suggest that the actions of NT3 and GDNF converge at the Ret/GDNF-receptor to enhance survival of the developing sympathetic neurons through activation of the phosphatidylinositol (PI) 3-kinase/Akt pathway.

Animals↗