Showing papers by "University of Tokyo published in 1978"

Aphidicolin Prevents Mitotic Cell Division by Interfering With the Activity of DNA Polymerase-Alpha

Abstract: THE study of the control of DNA synthesis would be helped if a variety of chemicals which influenced DNA synthesis in various ways was available. We have searched for chemicals which prevent mitotic division of sea urchin embryos, which requires DNA synthesis, but do not prevent meiotic divisions of starfish oocytes, which are independent of DNA synthesis1. Aphidicolin2 (I) is one such compound. Furthermore, recent experiments have shown that aphidicolin selectively inhibits the activity of DNA polymerase-α obtained from regenerating rat liver without interfering with the activity of DNA polymerase-β and mitochondrial DNA polymerase3. The function of the DNA polymerases in the complex process of DNA replication is not known. Correlative studies of DNA synthesis and the level of DNA polymerase activity suggest that DNA polymerase-α may be important in DNA replication4. However, in certain cases, DNA polymerase-β and -γ also increase at the time of DNA synthesis, and attempts to specify which of the DNA polymerases is ‘replicative’ or to assign roles to the various polymerases have not yet been successful4. We report here evidence that prevention of cell division by aphidicolin in sea urchin embryos is due to selective inhibition of DNA polymerase-α activity. This study implies a functional role for this polymerase activity during replication of DNA.

Nitrogen isotope effects in the assimilation of inorganic nitrogenous compounds by marine diatoms

Abstract: Nitrogen isotope fractionation in the assimilation of inorganic nitrogenous compounds was studied using marine diatoms (Phaeodactylum tricornutum and Chaetoceros sp.). The isotopic composition (δ15N) of the diatoms ranged from 7 to ‐18‰ relative to that of the nitrogen source, i.e., ammonium, nitrite, or nitrate. When the growth was light‐limited, the isotope fractionation in nitrate assimilation was inversely correlated with the growth rate. The highest fractionation factor of 1.016 was obtained when the growth rate was as low as 0.025 day‐1. Fractionation was negligible when the growth, rate was higher than 1 day‐1. A steady‐state kinetic model was applied to explain the isotope fractionation in nitrate assimilation. The nitrogen isotope fractionation primarily takes place at the step of N‐O bond breaking in nitrate reduction to nitrite. The extent of the isotope fractionation associated with the nitrate uptake is very small, and barely exceeds the limit of detection.

Polymatroidal dependence structure of a set of random variables

Abstract: Given a finite set E of random variables, the entropy function h on E is a mapping from the set of all subsets of E into the set of all nonnegative real numbers such that for each A ⊆ E h(A) is the entropy of A . The present paper points out that the entropy function h is a β -function, i.e., a monotone non-decreasing and submodular function with h(O) = 0 and that the pair ( E, h ) is a polymatroid. The polymatroidal structure of a set of random variables induced by the entropy function is fundamental when we deal with the interdependence analysis of random variables such as the information-theoretic correlative analysis, the analysis of multiple-user communication networks, etc. Also, we introduce the notion of the principal partition of a set of random variables by transferring some results in the theory of matroids.

Denitrification and ammonia formation in anaerobic coastal sediments.

Abstract: Simultaneous determinations of nitrogen gas production, ammonia, and particulate organic nitrogen formation in the coastal sediments of Mangoku-Ura, Simoda Bay, and Tokyo Bay were made by using the 15N-label tracer method. The rate of nitrogen gas production in the sediment surface layer was about 10−2 μg atom of N per g per h, irrespective of the location of the sediments examined. [15N]ammonia and -particulate organic nitrogen accounted for 20 to 70% of the three products, and after several hours of incubation, the major fraction of nondenitrified 15N in Mangoku-Ura and Simoda Bay sediments was recovered as ammonia. In Tokyo Bay sediments, particulate organic nitrogen was produced at a greater rate than was ammonia. The reduction rate data suggest that the pathway of nitrate reduction to ammonia is important in coastal sediments.

Reliability of a tsunami source model derived from fault parameters

Abstract: Numerical experiments of tsunami generation and propagation are carried out for five earthquakes which occurred off the Pacific coast of the Tohoku and Hokkaido districts. The tsunami sources used in the experiments are the vertical displacement field of the sea bottom derived from the seismic fault model for each earthquake. Water surface disturbances are computed by a finite difference hydrodynamical method with finer grids in shallower water. The comparison of the computed tsunami behavior with available tsunami records along the coast shows that the distribution of observed tsunami heights can be explained in the first approximation by seismic fault models while the observed heights are 1.2 to 1.6 times larger than the computed heights. An example of a fault model inferred from seismic data (June 12, 1968) which is not suitable for a tsunami source is presented.

Cellular and subcellular mechanisms of photodynamic action: the 1o2 hypothesis as a driving force in recent research

Abstract: — Since 1972 the protective (quenching) effect of N3- and the enhancing effect of D2O have been used in combination to demonstrate 1O2 (1Δg) as the major reactive intermediate in the dye-sensitized photooxygenation of biomolecules in in vitro systems. Extended application to in vivo systems has recently begun, producing some results which generally support the involvement of 1O2 pathways in the photosensitization processes. The use of other 1O2 quenchers and acceptors has also been increasing. In the application of these techniques as diagnostic tests for 1O2 participation in in vivo systems, careful examination of the experimental conditions should be made with respect to the quenching capability and accessibility of D2O in the specified cellular environment. Furthermore, the diffusive nature of 1O2, generation sites, generation efficiencies, the location and type of sensitizers, and the reactivity of 1O2 with presumed target structures in the cell should also be taken into account in the interpretation. Recent studies illustrating the importance of these factors are discussed. Finally, a tentative picture of the mode of in vivo photodynamic activity of common dye sensitizers is outlined.

Studies of a calcium-activated neutral protease from chicken skeletal muscle. I. Purification and characterization.

Abstract: A calcium-activated neutral protease was purified 2,700-fold over the crude extract from chicken skeletal muscle. The purified protease migrated as a single band on polyacrylamide gel electrophoresis with or without SDS. Its molecular weight was 80,000 and pH optimum for activity was 7.7. The activity required strictly the presence of calcium (optimum concentration: 1.8 mM) or strontium (optimum concentration: 10 mM) ions. The protease was inhibited by leupeptin, which is known to be a strong inhibitor of papain, cathepsin B, trypsin, and plasmin.

Collision of the izu-bonin arc with central honshu: cenozoic tectonics of the fossa magna, japan

Abstract: The Izu-Bonin arc joins with Honshu at the Fossa Magna where pre-Miocene terrains bend in a cusp form. The Miocene terrains in the region also have a northward-convex structure north of the Izu Peninsula. Moreover, highly compressive deformation, Quaternary strong uplift and anomalous trajectories of crustal stress axes also characterize this region.These features of central Honshu at the junction are explained well by assuming that a north-south trending plate boundary has been located off central Honshu since the late Cretaceous. The bend of the terrains was formed for the most part in the early Tertiary by buoyant subduction of aseismic ridges lying along the north-south trending transform fault.The Izu-Bonin arc, which was developed along this transform fault, has been dragged northward by oblique subduction of the Pacific plate and underwent subduction beneath central Honshu during the late Tertiary. In the early Quaternary, the Izu Block (the Izu Peninsula) of the Izu-Bonin arc collided with central Honshu and is pushing it north-northwestward. It is very likely that the triple junction off central Honshu has been located at its present position relative to Honshu since the late Mesozoic.

Fault mechanism and recurrence time of major earthquakes in southern Kanto district, Japan, as deduced from coastal terrace data

Abstract: The southern Kanto region has had two shocks of magnitude 8 or greater during the past 1,000 years. They were the 1703 and 1923 earthquakes, which occurred along the Sagami trough, a northeastern boundary of the Philippine Sea crustal plate in contact with the Asian plate. Although they occurred in nearly the same region, the 1703 earthquake was significantly different from the 1923 earthquake in the distribution of coastal uplift and tsunami height. The 1703 earthquake deformation is described on the basis of the height of the marine terraces along the coast of the southern Kanto region. The 1703 earthquake is interpreted, as is the 1923 earthquake, as the result of low-angle right-lateral faulting with a thrust component at the plate boundary. However, the fault surface in 1703 was longer (about 200 km) and was located farther east than that of the 1923 earthquake. On the basis of the pattern of coastal uplift and the trend of the Sagami trough, the fault surface of the 1703 earthquake can be divided into three planes, which involve the eastern part of the source region of the 1923 earthquake to the west (plane A), the Kamogawa submarine cliff in the middle (plane B), and a segment near the source region of the 1953 Boso-Oki earthquake (M equals 8.0) to the east (plane C). The Boso and Miura Peninsulas in the sourthern Kanto region have been uplifted during at least the last 6,000 years, and major uplifts have been accompained by earthquakes like those of 1703 and 1923 many times. The recurrence time of similar uplifts is estimated at 800 to 1,500 years on the basis of the numbers of the uplifted Holocene terraces in the Boso Peninsula, the rate of upheaval during the last 6,000 years, and the present geodetic data. Thus, it is unlikely that major earthquakes such as the 1703 and 1923 earthquakes will occur in the same segments in the near future. The Oiso area, however, which is located west of the western end of the 1703 faulting, seems higher in seismic risk than the other parts of the Sagami trough fault, because the sum of the recent uplift in the 1703 and 1923 earthquakes in that area is significantly less than the average rate of uplift there during the past 6,000 years. /Author/

Spin Fluctuation Theory of Itinerant Electron Ferromagnetism –A Unified Picture

Abstract: Spin fluctuations and the thermodynamical properties of itinerant electron ferromagnets are discussed from a general point of view by using a simple model with a small number of physical parameters and approximations in the functional integral formalism. We give unified expressions for the Curie temperature and the magnetic susceptibility which interpolate between the weakly and strongly ferromagnetic limits. In general, both the transversal and longitudinal components of the local spin fluctuations contribute to the Curie constant and the former (latter) is predominant in the local moment (weakly ferromagnetic) limit. It is pointed out that the amplitude of the local spin fluctuations can be saturated when there is an upper or lower bound of the energy band not too far from the Fermi level, resulting in a Curie-Weiss susceptibility of a local moment type, even without well-defined local moments. A transition between two different kinds of local spin states can also be expected in some cases.

Influence on blood pressure of renal isografts between spontaneously hypertensive and normotensive rats, utilizing the F1 hybrids.

Abstract: The F1 hybrids (F1) of spontaneously hypertensive rats (SHR) and Wistar rats (W), whose kidneys were transplanted from SHR at the age of 10 weeks and 20 weeks, showed significant elevation of blood pressure (BP) for 11 weeks after the transplantation In F1 with W or F1 kidneys BP was decreased near to the normal level F1 whose kidneys were transplanted from SHR or W showed low renin activity both in plasma and the kidney It is suggested that BP of SHR is probably determined by the renal pro-hypertensive factor(s) other than renin influencing on sympathetic nerves through central nervous systems

New symmetry in sd boson model of nuclei - group o(6)

Abstract: We suggest that, within the framework of the interacting-boson model, the group O(6) of orthogonal transformations in six dimensions may be useful in classifying nuclear spectra at the end of major shells. We derive analytic expressions for the energy levels and electromagnetic transition rates in this limit.

Direct inhibitory synaptic linkage of pontomedullary reticular burst neurons with abducens motoneurons in the cat.

Abstract: 1. Unit spikes of burst neurons were extracellularly recorded in the pontomedullary reticular formation of the cat. These neurons were identified by their burst activity coincident with the quick inhibitory phase of the contralateral abducens nerve during vestibular nystagmus and their antidromic activation from the contralateral abducens nucleus. 2. When the extracellular field potentials in and near the abducens nucleus were triggered by spikes of a contralateral burst neuron, the averaged potential consisted of an early di- or triphasic spike and a late slow positive wave. The early spike was an action current caused by impulses conducting along the axon of the burst neuron. 3. The action potentials of a contralateral burst neuron were employed to trigger a post-spike average of the membrane potential of abducens motoneurons. Then unitary IPSPs with monosynaptic latencies were revealed. This provided direct evidence that the burst neurons are inhibitory in nature. The amplitudes of unitary IPSPs ranged from 18 to 220 μV. Each inhibitory burst neuron branched widely in the abducens nucleus and was estimated to make inhibitory connections with approximately 60% of the motoneuron pool. 4. The post-spike average of compound potentials of the abducens nerve triggered by action potentials of contralateral single inhibitory burst neurons revealed inhibition of spike activity with latencies and time courses compatible with those of unitary IPSPs in motoneurons. The inhibition was observed with all inhibitory burst neurons tested.