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S Asakura

Publications and source records attributed to S Asakura.

At least 127 records · Page 7Linked to original sources
PubMed1984

Two-state model for bacterial chemoreceptor proteins. The role of multiple methylation.

To help understand the bacterial chemotactic response of excitation and adaptation, we propose a simple two-state model for receptor proteins (methyl-accepting chemotaxis proteins), in the light of evidence that they undergo multiple methylation in a preferred order. The model includes the following assumptions. (1) The receptor protein is in rapid equilibrium between two conformations, S and T, and the equilibrium shifts towards the T form as the number of methyl groups increases. (2) Attractants bind to the S form of the receptor, repellents bind to the T form, and both classes of ligand shift the S/T equilibrium according to the mass-action law. (3) The S form of the receptor accepts methyl groups one by one in a definite order, while the T form releases the methyl groups in the reverse order. Methylation and demethylation are slow reactions, and changes in the total number of methyl groups lag behind shifts in the S/T equilibrium. (4) The pattern of bacterial swimming at any moment is determined by the partition of the receptor between the two conformations, with tumbling frequency being a monotonically increasing function of the total T fraction of the receptor. This model shows that, if the receptor satisfies two sets of relationships imposed on its equilibrium and kinetic constants, it can maintain the steady-state total T fraction essentially constant over a broad range of ligand concentration, enabling cells to adapt to large changes in chemical environment. A stepwise change in ligand concentration leads to a rapid change in the total T fraction (excitation), followed by a slow relaxation process (adaptation). Computer simulations have been made of the whole response process, employing a receptor with six methylation sites per molecule and assuming simple sets of parameters. The results are in general agreement with published data on receptor methylation, as well as with a variety of observations of bacterial chemoresponse. Multiple methylation of the receptor proves to be necessary for the cells to respond sensitively to environmental changes.

Bacterial Physiological Phenomena↗
PubMed1984

Multidomain of flagellin.

Scanning microcalorimetric and circular dichroism studies of the normal and mutant flagellins of Salmonella suggest that they have a multidomain structure in common. Flagellin polymers (flagella) are depolymerized irreversibly into monomers as the temperature is raised, and the monomers undergo denaturation reversibly when cooled and heated again. The calorimetric enthalpy of this reversible process is twice as large as the van't Hoff enthalpy, suggesting that flagellin monomers contain two co-operative regions that melt independently at the same temperature. In all flagellin specimens examined, the ellipticity at the same temperature. In all flagellin specimens examined, the ellipticity at 222 nm of polymers at room temperature is 1.6 times as large as that of monomers, and the dependence of ellipticity on temperature takes place in the same temperature intervals in which calorimetric effects take place. From these results, we propose that flagellin molecules consist of several domains, two of which are distinctly structured in monomers at room temperature, while the others acquire more regular structures during polymerization.

Bacterial Proteins↗
PubMed1984

Polymorphic transition of the flagellar polyhook from Escherichia coli and Salmonella typhimurium.

Bacterial flagellar polyhook fibers were reversibly transformed into a set of helical forms depending on pH, ionic strength and temperature. Electron microscopy with formalin fixation and freeze-drying was useful for observing three-dimensional shapes of various polyhook helices and determining their helical handedness. A Cartesian plot of curvature against twist for these polyhook helices gave a sinusoidal curve as in the case of the polymorphic forms of flagellar filament. In the study on the polymorphism of flagellar filaments. Calladine (1976, 1978) and Kamiya et al. (1979) pointed out that such a relation in the polymorphic forms could be derived from the assumption that the subunits on the near-longitudinal (11-start) helical lines should work as elastic fibers (protofilaments) having two distinct states of conformation. In contrast, the observed twist for the polyhook helices is too large to be explained by the same assumption. Instead, we must assume that subunits on the strongly twisted, 16-start helical line should work as the co-operative protofilament.

Elasticity↗
PubMed1984

Age specific mortality trends in the U.S.A. from 1960 to 1980: divergent age-sex-color patterns.

Trends in age-specific mortality (10-year age groups, 5-74) for the U.S. population were reviewed for all causes of death from 1960 to 1980. The age-specific mortality rate generally declined. However, the following age-sex-color groups showed divergent mortality trends compared to those of other groups: (1) The death rates for white male teenagers and young adults (ages 15-24 and 25-34) increased during 1960s and stayed at the same level during 1970s. The ratio of male to female deaths for white teenagers and young adults (15-24 and 25-34) increased over both decades, although the mortality rate for white women age 15-24 increased during the 1960s. (2) Non-white men age 15-24 and 25-34 experienced biphasic mortality trends, with a rise peaking in 1971 and then a fall. (3) The mortality ratios, non-white to white men, age 25-34 and 35-44, were far higher then those of other age groups. (4) The mortality ratios, non-white males to females, increased steadily for all age groups, and those of age groups 15-24 and 25-34 turned up sharply. Selected causes of death (1960-1977) were reviewed to uncover reasons for the unfavorable mortality trends among males. The following causes contributed to rising mortality among males: (a) accidents, suicide, and homicide for white and non-white teenagers and young adults, age 15-24, 25-34 and 35-44; (b) suicide and homicide for non-white men age 45-54; (c) cirrhosis of the liver for white men age 35-44 and for non-white 25-34, 35-44 and 45-54; (d) malignant neoplasms for white men age 35-44 and for non-white age 45-54.

Accidents↗
PubMed1984

Alcohol consumption, blood pressure and stroke mortality in Japan.

The relationship between the national blood pressure level of an over 10,000 member representative sample of the population and alcohol consumption, using the time-series data during the period 1956-1980 was analysed. Analysis by multiple regression analysis showed alcohol consumption to be significantly related to the mean systolic blood pressure level for men independent of the treatment rate of hypertension, obesity, salt consumption and smoking rate. The relationship between alcohol consumption and stroke mortality using the age-adjusted stroke mortality for the middle-aged and alcohol consumption by prefecture (an administrative district of a province in Japan), in 1975 was also investigated. Stroke mortality for middle-aged men was highly significantly related, that for women was borderline but still significantly related, and the male:female ratio of the age-adjusted stroke mortality was also highly significantly related to alcohol intake. Thus, alcohol intake may play a role in increasing blood pressure levels and precipitate stroke, although it is possible that other confounding factors related to alcohol drinking may be related to blood pressure and also to stroke mortality.

Adult↗
PubMed1983

Posterior ischemic optic neuropathy. I. Blood supply of the optic nerve.

The blood supply of the posterior optic nerve was investigated in 10 monkeys after an injection of synthetic resin into the carotid arteries. The posterior intraorbital and intracanalicular optic nerves were supplied by a centripetal vascular system, formed by the pial vessels arising from the first branches of the ophthalmic artery. Superior and inferior vascular semicircles were detected in the intracanalicular optic nerve. The intracranial optic nerve was supplied by branches of the internal carotid artery, anterior cerebral artery and/or anterior communicating artery, and ophthalmic artery.

Animals↗
PubMed1982

Polymorphic transition in bacterial flagella.

The basic structure of the shaft of the bacterial flagellum is described and an account is given of work on polymorphism to date. The flagellum of wild-type Salmonella SJ670 has a characteristic left-hand helical form from pH 8 to pH 6, but undergoes two sharp transitions to other definite forms as the pH is lowered. The first transition, to a tight coil, can be followed by flow-birefringence. The flow-birefringence curve shows no evidence of hysteresis. Other details of the polymorphism, including the transitions which occur at high pH and at various KCl concentrations, are shown in a 'phase diagram'. Details of the transformation were studied by observing individual reconstituted flagella under dark-field light microscopy, while varying the bathing medium. Under some conditions, stress due to flow of the medium influences the transition. Under constant flow, alteration between two helical forms of opposite hand was sometimes observed. The two-state model is introduced to account for the helical structure and the polymorphism. Its prediction, that the two possible straight forms should have definite and opposite values of twist, is shown to agree with optical diffraction studies. Certain straight mutants are mentioned which show a novel feature in the diffraction pattern, probably due to a periodic perturbation of the helical lattice. The co-polymerisation of flagellins from straight mutants of the two different types yields a range of forms similar to the natural polymorphs. The implications of this finding are discussed.

Bacteria↗
PubMed1980

In vitro polymerization of polyhook protein from Salmonella SJW880.

Polyhooks were isolated from Salmonella SJW880, a non-flagellated mutant, and purified by cesium chloride density gradient centrifugation. The polyhooks were disintegrated into protein subunits (monomer) by heat in the absence of salt. The monomer was repolymerized in the presence of moderately high concentrations of sodium citrate at neutral pH. Three types of polymer were produced. One type of polymer, produced at room temperature and at citrate concentrations less than 0.3 M, had no regular shape and no definite thickness. Another type of polymer, produced at room temperature and at citrate concentrations greater than 0.4 M, had a straight shape and a similar thickness to that of polyhook but was easily dissociated into monomer in the absence of salt. A third type of polymer was produced at low temperature, independently of the concentration of citrate, and seemed to be a tubular polymer with a thickness similar to that of polyhook but had no helical curvature. However, this type of polymer was shown to have a structure locally the same as that of polyhook by electron microscopic observation, optical diffraction and circular dichroism measurements.

Bacterial Proteins↗