PubMed Health⌕ Search

Biomedical subjects

E Katayama

Publications and source records attributed to E Katayama.

At least 37 records · Page 2Linked to original sources
PubMed1996

Geometry of the flagellar motor in the cytoplasmic membrane of Salmonella typhimurium as determined by stereo-photogrammetry of quick-freeze deep-etch replica images.

The precise geometry of the flagellar basal structure anchored in the cytoplasmic membrane was determined by digital stereo-photogrammetry of the images captured by quick-freeze deep-etch replica electron microscopy. In order to examine the structure on the periplasmic side of the membrane, we analyzed the MS ring complexes of Salmonella typhimurium overproduced in the cytoplasmic membrane of Escherichia coli. The rod, the S ring, and the shoulder of the M ring were exposed to the periplasm. On the cytoplasmic side of the membrane, small bumps corresponding to the cytoplasmic rod were discernible. We also examined the intact inner surface of the cells of polyhook mutant which was prepared by a new protocol and found the bell-shaped structure extending from the membrane towards the cytoplasm. It was identified as the C ring, since it was located at the base of the polyhook. Various dimensions of the MS ring complex and the C ring projecting from the membrane were determined by digital stereo-photogrammetry, and a three-dimensional model of the total basal structure is presented.

Cell Membrane↗
PubMed1996

Physiological role of insulin-like-growth-factor-binding protein-4 in human folliculogenesis.

Insulin-like growth factor (IGF)-I and IGF-II, and their binding proteins (IGFBPs) have been demonstrated to play important roles in follicular development as intraovarian regulators. Previous studies have demonstrated that the follicular fluid of atretic follicles contains high levels of IGFBP-2 and IGFBP-4, which are known to inhibit the action of IGFs. In this study, we identified IGFBP-4 protease activity in the follicular fluid of developing but not atretic follicles. To elucidate the regulation mechanism of IGFBP-4 proteolytic activity in the ovary, cultured luteinized granulosa cells (GCs) were incubated with various hormones, and proteolyzed IGFBP-4 in the medium was analyzed. IGFBP-4 proteolytic activity was increased when GCs were incubated with IGFs, estradiol or follicle-stimulating hormone (FSH) but not with testosterone. We also showed that IGFBP-4 inhibited IGF-1-induced estradiol release by GCs while proteolyzed IGFBP-4 did not. These results suggest that human luteinized GCs produce IGFBP-4 protease, and that FSH and IGFs may stimulate folliculogenesis by modulating IGFBP-4 degradation in the ovary.

Cells, Cultured↗
PubMed1996

[Electron microscopy for the studies of membrane transport proteins].

Electron microscopy gives the real images of individual protein molecules, providing unique means in the structural research of membrane-transport proteins. Various techniques for the preparation of specimens for transmission electron microscopy were briefly described. Emphases were put on the recent progress of quick-freeze cryo-electron microscopy, including cryotransfer and freeze-fracture deep-etch replication. Exploiting the advantage of the latter technique, we visualized the in situ structure of inositol 1,4,5-trisphosphate receptor molecules in the smooth-surfaced endoplasmic reticulum (sER) membrane of the Purkinje neuron in bovine cerebellum. The tetrameric receptor molecules were unexpectedly small and formed a two-dimensional crystalline array on the surface of the cisternal stacks derived from sER. Its structural characteristics were discussed in comparison with the ryanodine-receptor, the other intracellular Ca2+ -channel.

Animals↗
PubMed1995

Myosin from alga Chara: unique structure revealed by electron microscopy.

Cytoplasmic streaming is a fundamental process for the transport of molecules and organelles in plant cells. A myosin-like protein responsible for cytoplasmic streaming in fresh water alga, Chara corallina, has been purified. Electron micrographs of this protein revealed that it has two heads with similar size and shape to those of muscle myosin (myosin II) but its tail was shorter than that of muscle myosin with a globular structure at its distal end like that of myosin V. The myosin cosedimented with vesicles composed of phosphatidyl serine like other non-muscle myosin species involved in intracellular transport.

Actins↗
PubMed1995

Effect of caldesmon on the assembly of smooth muscle myosin.

Smooth muscle myosin filaments are much less stable than the skeletal muscle counterpart. Smooth myosin requires higher concentration of Mg2+ than skeletal myosin to form thick filaments and addition of ATP disassembles the dephosphorylated smooth muscle myosin filaments into monomers but not phosphorylated ones. We found that the addition of caldesmon to dephosphorylated myosin induced the formation of the filaments under the conditions where myosin by itself is soluble or disassembled. Although the induced filaments were short at 1 mM Mg2+, they became medium sized and seemed like side polar filaments with prominent 14 nm periodicity at higher Mg2+ conditions (8 mM). In the presence of F-actin, myosin filaments induced by caldesmon were associated along actin filaments to form large structures. The association of actin and myosin filaments was observed only in the presence of caldesmon, suggesting that caldesmon cross-linked actin and myosin filaments. This cross-linking was disrupted by the addition of calmodulin. Caldesmon-induced filament formation of dephosphorylated myosin in the presence of Mg(2+)-ATP may explain the existence of myosin filaments in relaxed smooth muscle fibers. A similar effect of telokin on myosin filament assembly was also examined and is discussed.

Actins↗
PubMed1995

Mode of caldesmon binding to smooth muscle thin filament: possible projection of the amino-terminal of caldesmon from native thin filament.

The structure of smooth muscle thin filament was examined by various electron microscopy techniques, with special attention to the mode of caldesmon binding. Chemical cross-linking was positively used to avoid the dissociation of accessory proteins upon dilution. Caldesmon in reconstituted thin filament was observed as fine filamentous projections from thin filament. Native thin filament isolated from smooth muscle showed similarly numerous fine whisker-like projections by all the techniques employed here. Antibody against the amino-terminus of caldesmon labeled the end of such projections indicating the possibility that the amino-terminal myosin binding moiety might stick out from the shaft of the thin filament. Such whiskers are often projected out as a cluster to the same side of native thin filament. Further, we could visualize the assembly of dephosphorylated heavy meromyosin (HMM) with native or reconstituted thin filament forming "nonproductive" complex in the presence of ATP. The association of HMM to the shaft of thin filament was through subfragment-2 moiety, in accordance with biochemical studies. Some HMM particles bound closer to the thin filament shaft, possibly suggesting the presence of the second myosin-binding site on caldesmon. Occasionally two kinds of HMM association as such coexisted at a single site on this filament in tandem. Thus, we constructed a structural model of thin filament. The proposed molecular arrangement is not only compatible with all the biochemical results but also provides additional support for our recent findings (E. Katayoma, G. C. Scott-Woo, and M. Ikebe (1995) J. Biol. Chem. 270, 3919-3925) regarding the capability of caldesmon to induce dephosphorylated myosin filament, which explains the existence of thick filaments in relaxed smooth muscle cells.

Actin Cytoskeleton↗
PubMed1995

Cleavage of Shigella surface protein VirG occurs at a specific site, but the secretion is not essential for intracellular spreading.

The large plasmid-encoded outer membrane protein VirG (IcsA) of Shigella flexneri is essential for bacterial spreading by eliciting polar deposition of filamentous actin (F-actin) in the cytoplasm of epithelial cells. Recent studies have indicated that VirG is located at one pole on the surface of the bacterium and secreted into the culture supernatant and that in host cells it is localized along the length of the F-actin tail. The roles of these VirG phenotypes in bacterial spreading still remain to be elucidated. In this study, we examined the surface-exposed portion of the VirG protein by limited trypsin digestion of S. flexneri YSH6000 and determined the sites for VirG processing during secretion into the culture supernatant. Our results indicated that the 85-kDa amino-terminal portion of VirG is located on the external side of the outer membrane, while the 37-kDa carboxy-terminal portion is embedded in it. The VirG cleavage required for release of the 85-kDa protein into the culture supernatant occurred at the Arg-Arg bond at positions 758 to 759. VirG-specific cleavage was observed in Shigella species and enteroinvasive Escherichia coli, which requires an as yet unidentified protease activity governed by the virB gene on the large plasmid. To investigate whether the VirG-specific cleavage occurring in extracellular and intracellular bacteria is essential for VirG function in bacterial spreading, the Arg-Arg cleavage site was modified to an Arg-Asp or Asp-Asp bond. The virG mutants thus constructed were capable of unipolar deposition of VirG on the bacterial surface but were unable to cleave VirG under in vitro or in vivo conditions. However, these mutants were still capable of eliciting aggregation of F-actin at one pole, spreading into adjacent cells, and giving rise to a positive Sereny test. Therefore, the ability to cleave and secrete VirG in Shigella species is not a prerequisite for intracellular spreading.

Amino Acid Sequence↗
PubMed1995

Gene expressions of oxytocin and oxytocin receptor in cumulus cells of human ovary.

Oxytocin (OT) has been detected in mammalian granulosa-luteal cells during the early stages. The purpose of this study was to explore gene expressions of OT and OT receptor (OTR) in human cumulus cells. Cumulus cells enclosing a mature oocyte were obtained from 6 women undergoing clinical in vitro fertilization and embryo transfer programs. OT and OTR gene expressions were investigated by employing reverse transcription polymerase chain reaction and reverse transcription polymerase chain reaction/single-strand conformation polymorphism methods. OT gene expression in the cumulus cells was positive in 5 women and weakly positive in the remaining patient. The structure of OT mRNA in the cumulus cells was equivalent to that in human hypothalamus. OTR gene expression was also observed in the cumulus cells. This study is the first to describe the simultaneous expression of both OT and OTR genes in human cumulus cells. It is suggested that local OT plays some important roles in fertility through modification of the micro-environment around the oocyte.

Base Sequence↗
PubMed1994

Regulation and physiological role of insulin-like-growth-factor-binding protein-1 in human granulosa cells.

The present study was undertaken to elucidate the physiological role and the regulation of insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) in human luteinizing granulosa cells. IGFBP-1 abolished IGF-I-stimulated estradiol production by luteinizing granulosa cells in a dose-dependent manner with a 50% inhibitory concentration (IC50) of 0.27 nM. Similarly, IGFBP-1 inhibited 125I-IGF-I binding to granulosa cells. IGFBP-1 was identified by Western immunoblot and specific enzyme immunoassay in the granulosa-cell-conditioned medium after 24 h culture. Immunoreactive IGFBP-1 released into the medium was inhibited by both IGF-I and follicle-stimulating hormone dose-dependently with an IC50 of 0.14 and 0.13 nM, respectively, while human chorionic gonadotropin-stimulated IGFBP-1 release with a 50% effective dose (ED50) of 0.6 nM. These results suggest that IGFBP-1 is involved in follicular development and granulosa cell differentiation in the human ovary and that gonadotropins may influence IGF-I action by modifying IGFBP-1 levels within the ovary.

Binding, Competitive↗
PubMed1994

In vitro micro-autoradiography of atrial natriuretic peptide in biopsy specimens from patients with renal diseases.

We investigated the localization and density of atrial natriuretic peptide (ANP) receptors in human renal biopsy specimens by using in vitro micro-autoradiography (ARG) of [125I]-alpha-human (1-28) ANP. In a preliminary study, we measured the effect of storing tissue samples on ANP binding, using in vitro micro-ARG of Wistar rat kidney under optimal conditions. Duration of the preservation period did not affect ANP binding to renal tissue until samples had been stored at -30 degrees C for two years. A total of 11 human renal tissues were used to assay binding of ANP-ARG, including normal tissue obtained after nephrectomy because of renal cancer. ANP binding occurred predominantly within the glomerulus and, to a lesser extent, in the tubular region both in rat kidney sections and in human renal biopsy specimens. The density of ANP binding, calculated by counting grains in fixed areas, was compared with normal and pathological tissues. The density of grains tended to decrease in patients with renal dysfunction and hypertension except for one case of IgA nephropathy with normal renal function and blood pressure. The density of grains increased in a patient with nephrogenic diabetes insipidus. In the present study, we have established a method that uses in vitro micro-ARG for assessing ANP binding in human biopsy specimens.

Animals↗
PubMed1993

Gross structural features of myosin head during sliding movement of actin as studied by quick-freeze deep-etch electron microscopy.

With quick-freeze deep-etch electron microscopy coupled with mica-flake technique, I showed previously that myosin subfragment-1 (S1) attached to F-actin in the presence of ATP is short and rounded, in contrast to its elongated and tilted appearance under rigor condition [J. Biochem. 106, 751-770 (1989)]. I further indicated that each head of heavy meromyosin (HMM) changes its configuration in a likely manner as above by the addition of various nucleotides, i.e. heads were pear-shaped in the absence of nucleotide, in a ball-on-a-stick appearance when complexed with ADP and strongly kinked to the particular direction in the presence of ATP or ADP.Vi [J. Muscle Res. Cell Motility 12, 313 (1991)]. Such morphological data not only corroborates the independent biophysical evidences suggesting gross conformational changes of myosin head upon binding ATP or ADP.Vi, but also provide strong evidence for the distinct polarity in the structure of each myosin head. Negatively stained image of chemically cross-linked acto-S1 also included cross-bridges sharply kinked to the same direction, confirming the above observation. Attempts were made to examine if such conformational change of myosin cross-bridge occurs during actomyosin superprecipitation. Samples were quick-frozen during rapid turbidity-increasing phase where actin filaments actively slide past myosin heads. The resultant image included actin-attached myosin heads all in a kinked configuration with the same polarity as observed for HMM. Several heads associated with a single actin filament were bent to the same direction suggesting that myosin heads might be in a kinked configuration with distinct polarity during contraction.

Actins↗
PubMed1993

Cooperativity in F-actin: chemical modifications of actin monomers affect the functional interactions of myosin with unmodified monomers in the same actin filament.

We have chemically modified a fraction of the monomers in actin filaments, and then measured the effects on the functional interaction of myosin with unmodified monomers within the same filament. Two modifications were used: (a) covalent attachment of various amounts of myosin subfragment-1 (S1) with the bifunctional reagent disuccinimidyl suberate and (b) copolymerization of unmodified actin monomers with monomers cross-linked internally with 1-ethyl-3-(dimethylaminopropyl)-carbodiimide. Each of these modifications abolished the interaction of the modified monomers with myosin, so the remaining interactions were exclusively with unmodified monomers. The two modifications had similar effects on the interaction of actin with myosin in solution: decreased affinity of myosin heads for unmodified actin monomers, without a change in the Vmax of actin-activated myosin ATPase activity. However, modification (b) produced much greater inhibition of actin sliding on a myosin-coated surface, as measured by an in vitro motility assay. These results provide insight into the functional consequences of cooperative interactions within the actin filament.

Actins↗
PubMed1993

[Human embryo freezing with dimethylsulfoxide (DMSO) and sucrose as cryoprotectants].

176 supernumerary human embryos following treatment by IVF were cryopreserved with dimethylsulfoxide (1.5M) and sucrose (0.1M) as cryoprotectants. The embryos were frozen at the early cleavage stage (48-96 hours after insemination) in the programmable freezer, by means of the protocol providing for slow cooling until -40 degrees C and slow thawing. The survival rate (50% or more blastomeres were intact) after thawing was higher for the embryos at the 8 cell stage to the morulla stage (60-96 hours after insemination) than for the embryos at the 4 to 6 cell stage (48-60 hours after insemination) (87% and 66%, p < 0.001), and the overall survival rate was 80% (140/176). Out of 62 transfer cycles, 11 pregnancies (17.7%) and 6 deliveries (9.7%) were achieved. No fetal malformation or chromosomal aberration was observed.

Cryopreservation↗
PubMed1993

Structure of photoreceptive membranes of Drosophila compound eyes as studied by quick-freezing electron microscopy.

Photoreceptive membranes of Drosophila compound eyes were studied by quick-freezing electron microscopy. The quick-frozen photoreceptive microvilli appeared cylindrical in shape either when they were freeze-substituted or freeze-fractured. Deep-etch replication revealed the extracellular surfaces of microvilli which were covered by various particles arranged in a helical manner. The protoplasmic surfaces were covered by more regular helical rows of particles about 10 nm in diameter. When rhodopsin content of the photoreceptive membranes was reduced by vitamin A-deficiency, the intramembrane particles drastically decreased resulting in the disappearance of particles in rows. Our results strongly suggest the regular arrangement of rhodopsin molecules in invertebrate photoreceptive membranes.

Animals↗
PubMed1992

Sliding velocity of isolated rabbit cardiac myosin correlates with isozyme distribution.

To investigate the relationship between the mechanical and biochemical properties of cardiac myosin, the sliding velocity of isolated cardiac myosin obtained from both euthyroid and hyperthyroid rabbits on actin cables was measured with an in vitro motility assay system. Ten rabbits (T) were treated with L-thyroxine to induce hyperthyroidism, and eight nontreated animals (N) were used as controls. Myosin was purified from the left ventricles of anesthetized animals. Myosin isozyme content was analyzed by the pyrophosphate gel electrophoresis method, and myosin adenosinetriphosphatase (ATPase) activity was determined on the same sample. Long well-organized actin cables of green algae, Nitellopsis, were used in the in vitro motility assay. Small latex beads were coated with purified cardiac myosin and introduced onto the Nitellopsis actin cables. Active unidirectional movement of the beads on the actin cables was observed under a photomicroscope, and the velocity was measured. The velocity was dependent on ATP concentrations, and the optimal pH for bead movement was approximately 7.0-7.5. The mean velocity was higher in T than in N (0.66 +/- 0.12 vs. 0.32 +/- 0.09 micron/s, P less than 0.01). Both Ca(2+)-activated ATPase activity and the percentage of alpha-myosin heavy chain were also higher in T than in N (0.691 +/- 0.072 vs. 0.335 +/- 0.072 microM Pi.mg-1.min-1, P less than 0.01, and 79 +/- 12 vs. 26 +/- 7%, P less than 0.01, respectively). The velocity of myosin closely correlated with both Ca(+2)-activated myosin ATPase activity (r = 0.87, P less than 0.01) and the percentage of alpha-myosin heavy chain (r = 0.87, P less than 0.01).

Animals↗
PubMed1991

[An analysis of factors associated with ectopic pregnancy following in vitro fertilization and embryo transfer].

Five ectopic pregnancies occurred in 75 in vitro fertilization and embryo transfer (IVF-ET) pregnancies (6.7%) in Ogikubo Hospital IVF program between 1985 and 1989. The indication for IVF in 70 pregnancies was a tubal factor. Thirty cases were among 70 pregnancies with hydrosalpinx, and 40 cases were with other tubal conditions. All of the five cases had tubal disease. Four of them had hydrosalpingos. The percentage of ectopic pregnancies for the 30 pregnancies with hydrosalpinx was 13.3%, while for 40 pregnancies with other tubal conditions it was 2.5%. However, there was no significant difference between the two groups. No correlation was found in other parameters including superovulatory methods, oocyte recovery procedure, number of embryos transferred, embryo transfer procedure, and endocrine changes after embryo transfer. In this study, we were unable to identify a difference between ectopic pregnancy and intra-uterine gestation in IVF-ET. However, further study is required to clarify whether hydrosalpinx increases the risk of ectopic pregnancy in IVF-ET.

Adult↗
PubMed1989

Characteristics of the myosin and tropomyosin binding regions of the smooth muscle caldesmon.

Limited digestion of caldesmon by alpha-chymotrypsin generates mainly 110, 80, 60, 38, and 28 kDa fragments. Affinity chromatography of these fragments on columns immobilized with myosin, HMM, or tropomyosin showed that the bound fraction from these columns was similar and it contained 110, 80, 60 and 28 kDa fragments. These fragments did not bind to myosin filaments, acto-HMM, actin or tropomyosin-actin in the solution, and they had no effect on the actin-activated ATPase of HMM. In contrast, the flow-through fraction from these affinity columns inhibited the actin-activated ATPase. Binding studies revealed that the 38 kDa fragment and its break down products bound to actin and tropomyosin-actin, and they were released partially from actin by calmodulin with a concomitant increase in the ATPase activity. These results indicate that, unlike the actin binding domain, the myosin and tropomyosin binding domains require the caldesmon molecule to be intact in order to exert their effects on the protein-protein interaction.

Actins↗