Does Paramecium sense gravity?

In order to get an insight into the cellular mechanisms for the integration of the effects of gravity, we investigated the gravitactic behaviour in Paramecium. There are two main categories for the model of the mechanism of gravitaxis; one is derived on the basis of the mechanistic properties of the cell (physical model) and the other of the physiological properties including cellular gravireception (physiological model). In this review article, we criticized the physical models and introduced a new physiological model. Physical models postulated so far can be divided into two; one explaining the negative gravitactic orientation of the cell in terms of the static torque generated by the structural properties of the cell (gravity-buoyancy model by Verworn, 1889 and drag-gravity model by Roberts, 1970), and the other explaining it in terms of the dynamic torque generated by the helical swimming of the cell (propulsion-gravity model by Winet and Jahn, 1974 and lifting-force model by Nowakowska and Grebecki, 1977). Among those we excluded the possibility of dynamic-torque models because of their incorrect theoretical assumptions. According to the passive orientation of Ni(2+)-immobilized cells, the physical effect of the static torque should be inevitable for the gravitactic orientation. Downward orientation of the immobilized cells in the course of floating up in the hyper-density medium demonstrated the gravitactic orientation is not resulted by the nonuniform distribution of cellular mass (gravity-buoyancy model) but by the fore-aft asymmetry of the cell (drag-gravity model). A new model explaining the gravitactic behaviour is derived on the basis of the cellular gravity sensation through mechanoreceptor channels of the cell membrane. Paramecium is known to have depolarizing receptor channels in the anterior and hyperpolarizing receptors in the posterior of the cell. The uneven distribution of the receptor may lead to the bidirectional changes of the membrane potential by the selective deformation of the anterior and posterior cell membrane responding to the orientation of the cell in the gravity field; i.e. negative- and positive-going shift of the potential due to the upward and downward orientation, respectively. The orientation dependent changes in membrane potential with respect to gravity, in combination with the close coupling of the membrane potential and the ciliary locomotor activity, may allow the changes in swimming direction along with those in the helical nature of the swimming path; upward shift of axis of helix by decreasing the pitch angle due to hyperpolarization in the upward-orienting cell, and also the upward shift by increasing the pitch angle due to depolarization in the downward-orienting cell. Computer simulation of the model demonstrated that the cell can swim upward along the "super-helical" trajectory consisting of a small helix winding helically an axis parallel to the gravity vector, after which the model was named as "Super-helix model". Three-dimensional recording of the trajectories of the swimming cells demonstrated that about a quarter of the cell population drew super-helical trajectory under the unbounded, thermal convection-free conditions. In addition, quantitative analysis of the orientation rate of the swimming cell indicated that gravity-dependent orientation of the swimming trajectory could not be explained solely by the physical static torque but complementarily by the physiological mechanism as proposed in the super-helix model.     

Formation of bioorganic compounds in aqueous solution induced by flames

Flames of flammable gases, when blown against a surface of an aqueous solution of organic compounds, were found to induce oxidation as well as other reactions in the solution. This reaction would be regarded as a new model for formation of bioorganic molecules in the primitive hydrosphere exposed to some radical-containing atmosphere.     

Surface ultrastructure of the tegument of Clonorchis sinensis newly excysted juveniles and adult worms.

The tegumental structures of newly excysted juveniles and adult worms of Clonorchis sinensis were studied using scanning and transmission electron microscopy. After excystation the juvenile's tegumental surface is characterized by knoblike protuberances and is armed almost entirely with numerous rows of small spines encircling the body. These spines are double- or triple-pointed on the anterior portion of the body and become single-pointed posteriorly. Four types of presumed sensory structures were observed as follow: A) ciliated knoblike papillae and B) nonciliated platelike papillae, both of which are arranged in rougly a bilaterally symmetrical pattern dorsally, ventrally, and laterally; C) rounded swellings of nonciliated papillae on the lips of the ventral and oral suckers, which are characterized in the transmission electron microscope by a rounded dense body in the apical bulb; and D) a sensory receptor with a bulbous projection having the appearance of a modified cilium, which was not found with SEM likely owing to its being enclosed by an extension of the tegument. In full-grown adult worms, the tegumental surface is knobbed or lobulated in various forms without surface spines. The tegumental structures in the adults appear to be clearly differentiated from those in the juveniles. Upraised, buttonlike papillae, each topped by a short cilium, which are similar to the Type A papillae in the juveniles, are distributed thickly around the oral and ventral suckers, and are rather randomly scattered over the remainder of the body. Some nonciliated swollen papillae were found on the lip of the ventral sucker.     

A new biologically active phenolic from Cattleya trianaei

A new phenolic, hydroxyeucomic acid, and dopamine were isolated from Cattleya trianaei and their biological activities examined.     

Affinity chromatography of trypsin and related enzymes. V. Basic studies of quantitative affinity chromatography.

A detailed study of the quantitative affinity chromatography of trypsin [EC 3.4.21.4] is reported here. Frontal chromatography using an enzyme solution of very low concentration on an affinity adsorbent gave the dissociation constant of the enzyme-immobilized ligand complex (Kd). Kd values determined under various conditions enabled us to discuss in detail the interaction of trypsin and affinity adsorbents (mainly Gly-Gly-Arg Sepharose). The pH dependence of Kd was consistent with that of the interaction of trypsin and product-type compounds. The effects of changes in temperature, ionic strength, dielectric constant, etc., were also studied. The Ki values of soluble competitive inhibitors can be determined by analysis of their effects on the elution volume of the enzyme. The values obtained were in good agreement with those obtained by kinetic analysis. The present method proved to be useful as a general procedure to investigate the interaction of a protein and a specific ligand.     

A hypotetraploid human T lymphoid cell line established by cell fusion.

A human T lymphoid cell line was established by cell hybridization technique from peripheral blood leucocytes of a patient with Sezary syndrome. The cells beared the surface antigens of human T lymphocyte specificity as demonstrated by immune cytolysis tests, but did not form E rosettes with sheep red blood cells. Isozyme patterns of enzymes in this line such as lactate dehydrogenase, glucose 6-phosphate dehydrogenase and esterase were of human type. The line had 79 chromosomes in modal number. This case supports the proposal that the production of tetraploids is favourable for establishment of cell lines.     

Random replication and random assortment model for plasmid incompatibility in bacteria

To understand the incompatibility between two related plasmids, both of which replicate in an autonomous state under a common control mechanism, we have developed a model that assumes a random choice mechanism for replication of plasmid copies and their random assortment into daughter cells upon cell division. Segregation kinetics by this model is analyzed mathematically and the number of generations required for segregation is calculated as a function of plasmid copy number per cell. The results obtained offer enough quantitative data to make our model reasonably realistic.     

Change in the intrinsic fluorescence of acetylcholine receptor purified from Narke japonica upon binding with cholinergic ligands

Effects of various cholinergic ligands on the intrinsic fluorescence of acetylcholine receptor purified from the electric organ of Narke japonica were investigated. Binding with acetylcholine decreased the fluorescence by 7–8%, and that with carbamylcholine by 4–5% at 20 °C. Decamethonium and d-tubocurarine did not affect significantly the fluorescence intensity, while hexamethonium enhanced it. These changes were completely inhibited by preincubation of the receptor with α-bungarotoxin, which indicated that the observed intrinsic fluorescence change was due to the specific binding of each ligand. Data of the quenching experiment using iodide ion as an extrinsic quencher suggested the occurrence of the conformational change in the receptor upon binding with various cholinergic ligands. Considering these results together with those on intrinsic fluorescence change, conformational change provoked by binding with acetylcholine or carbamylcholine seems to differ from that provoked by binding with other cholinergic ligands examined.     

A chaperonin from a thermophilic bacterium, Thermus thermophilus, that controls refoldings of several thermophilic enzymes.

A chaperonin has been purified from a thermophilic bacterium, Thermus thermophilus. It consists of two kinds of proteins with approximate Mr 58,000 and 10,000 and shows a 7-fold rotational symmetry from the top view and a "football"-like shape from the side view under the electron microscopic view. Its weak ATPase activity is inhibited by sulfite and activated by bicarbonate. ATP causes change of its mobility in nondenaturating polyacrylamide gel electrophoresis. The T. thermophilus chaperonin can promote in vitro refolding of several guanidine HCl-denatured enzymes from thermophilic bacteria. At high temperatures above 60 degrees C, where the native enzymes are stable but their spontaneous refoldings upon dilution of guanidine HCl fail, the chaperonin induces productive refolding in an ATP-dependent manner. No or very poor refolding is induced when the chaperonin is added to the solution aged after dilution. An excess amount of the chaperonin is inhibitory for refolding. At middle temperatures (30-50 degrees C), where spontaneous refoldings of the enzymes occur, the chaperonin arrests refolding in the absence of ATP and refolding is induced when ATP is supplemented. At temperatures below 20 degrees C, where spontaneous refoldings also occur, the chaperonin arrests the refolding but ATP does not induce refolding.