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J Xu

Publications and source records attributed to J Xu.

At least 1,243 records · Page 69Linked to original sources
PubMed1991

Phosphoenolpyruvate-insensitive phosphofructokinase isozyme from Thermus thermophilus HB8.

In the previous paper [Xu, J., Oshima, T., & Yoshida, M. (1990) J. Mol. Biol. 215, 597-606], we reported that phosphofructokinase from Thermus thermophilus is allosterically inhibited by phosphoenolpyruvate, which induces dissociation of the active four-subunit enzyme into an inactive two-subunit form. When T. thermophilus was cultured in a glucose-containing medium, another phosphofructokinase (PFK2) appeared in addition to the reported one (PFK1). The molecular weights of the native PFK2 molecule (132,000) and its subunit (34,500), which are slightly smaller than those of PFK1, suggest that PFK2 is also composed of four identical subunits. However, the hyperbolic kinetics and molecular form of PFK2 are not affected at all by phosphoenolpyruvate. The NH2-terminal amino acid sequences of subunits of PFK1 and PFK2 revealed that they are composed of very similar but different polypeptides.

Amino Acid Sequence↗
PubMed1991

Evaluation of a lens opacities classification system II (LOCS II) in the survey population-based sample.

In the field work of population-based research, 3 groups of eyes were graded by 2 observers in LOCS II. The reproducibility of LOCS II was evaluated by agreements (85%-100%) and k values (0.661-1) obtained in our study. The satisfying results show that LOCS II is not only easy to be learned and to be applied consistently by different observers, but also good reproducibility in the field work. The longitudinal cataract study is going to be performed in our plan.

Cataract↗
PubMed1991

[An investigation of glottic movement and vocal cord evoked electromyography following unilateral cricoarytenoid joint injuries in rabbits].

The unilateral cricoarytenoid joints of rabbits were bluntly injured. Observations on glottic movement and vocal cord evoked electromyography were performed. The results confirm that injury of the cricoarytenoid joint always causes disturbances in ipsilateral vocal cord movement. But the evoked electrical activities of the ipsilateral vocal cord muscles were normal not only in acute stage but also in chronic stage. The above results may provide the experimental basis for clinical differentiation of disturbances in glottic movement.

Animals↗
PubMed1990

Tetramer-dimer conversion of phosphofructokinase from Thermus thermophilus induced by its allosteric effectors.

Phosphofructokinase (PFKase) was purified from an extreme thermophile. Thermus thermophilus. Allosteric natures of T. thermophilus PFKase is similar to those of Bacillus stearothermophilus PFKase, that is, hyperbolic plots of the activity versus concentration of fructose 6-phosphate (F6P) were changed into a sigmoidal shape by the addition of phosphoenolpyruvate (PEP), while further addition of ADP caused it to revert to a hyperbolic shape. The native T. thermophilus PFKase has an Mr of 148,000 consisting of four 36,500 subunits. However, it exists as a two-subunit form of Mr 74,000 in the presence of PEP. The two-subunit form was catalytically inactive. The four-subunit enzyme was regenerated by addition of either F6P or Mg.ADP, or by removal of PEP from the solution. This reversible dissociation was observed within a wide range of pH (6.5 to 8.4) and temperature (4 degrees C to 65 degrees C). Thus, unlike PFKase from other sources, the allosteric kinetics of T. thermophilus PFKase can be explained well, at least qualitatively, by the dynamic equilibrium between the active four-subunit form and inactive two-subunit form that is modulated by PEP, F6P and Mg.ADP. Parallel suppression of the PEP-induced conversion in molecular form and kinetics by high concentrations of sulfate and phosphate supports the above explanation. Also, the observation that the degree of PEP inhibition was dependent on the protein concentration of the PFKase in the assay solution is consistent with the presence of this equilibrium.

Adenosine Diphosphate↗
PubMed1990

Light-evoked changes in extracellular calcium concentration in frog retina.

Light-evoked changes in extracellular Ca2+ concentration were recorded with Ca2(+)-selective microelectrodes in the retina of the frog eyecup. A Ca-decrease at light onset and offset was found in the inner plexiform layer, and its properties are consistent with it resulting from Ca2+ influx into activated neuronal terminals. In the subretinal space, a Ca-increase at light onset and a Ca-decrease at offset were observed, and these likely arise directly from photoreceptors. A slower ON Ca-decrease was also seen here. Because it survives pharmacological isolation of the photoreceptors from post-synaptic interactions, but not physical isolation of the retina from the pigment epithelium, this component probably depends on pigment epithelial activity.

Animals↗
PubMed1990

Identification and characterization of a regulated promoter element in the epidermal growth factor receptor gene.

We have identified a 36-base-pair proximal element (-112 to -77 relative to the AUG translation initiation codon) in the epidermal growth factor receptor 5' region that functions as a promoter; mediates inductive responses to epidermal growth factor, phorbol 12-myristate 13-acetate, and cyclic AMP; and acts in an orientation-independent manner. This region functions as an enhancer when transferred to a heterologous promoter containing a TATA box. Mutations within the 36-base-pair region alter function as assayed by reporter gene expression in recipient cells. A protein has been identified that demonstrates appropriate binding specificity to mutant DNA sequences that correlates with promoter activity observed in vivo. On the basis of DNA binding characteristics and size, the identified protein appears distinct from several previously identified transcription factors known to bind to G+C-rich regions.

Base Composition↗
PubMed1990

Toxicity of Irradiated Media for Xenorhabdus spp.

Bacterial isolates of the genus Xenorhabdus were shown to be extremely sensitive to photoproducts produced in a number of common media irradiated by fluorescent light. Two forms of toxic oxygen, hydrogen peroxide and superoxide radical, were produced in the media upon exposure to fluorescent light. The addition of pyruvate or catalase to the irradiated media eliminated the toxicity. The poor plating efficiencies previously reported for Xenorhabdus spp. are likely due to the uncontrolled exposure of media to ambient lighting.

Journal Article↗
PubMed1990

[A simplified polygraphic method for studying sleep in the rat].

Experiments were performed on 10 healthy Wistar rats with chronically implanted electrodes for the recording of electrocorticogram (ECoG), electro-oculogram (EOG), and electromyography (EMG). All the rats were prepared for the implantation of recording electrodes under 5% Ketamine (100 mg/kg i.p.) anesthesia. Four to six days after operation, the rat was put in an apparatus which was designed specifically sensitive to detect the movement of the animal without electrode on the body so that electroactogram (EAG) could be recorded readily. One group of experiment animal (n = 5), recorded ECoG, EAG, EOG and EMG simultaneously, was compared to another group (n = 5), recorded ECoG and EAG simultaneously. The results of experiments indicate that the ECoG, recorded from the the mesial frontal and occipital areas, have certain characteristics during different sleep phases, and the characteristics for classifying sleep phases by the two kinds of somnopolygram are similar. Therefore, simultaneous recording of the ECoG and EAG can be used to discriminate the sleep phases in the rat. In this way, the somnopolygraphic recording method for studying sleep in the rat would be simplified.

Animals↗
PubMed1990

[Effect of phenolic resin fluid on the dentin resistance].

SEM observation was made in the experiment to analyze the ultrastructure of resinified dentin. Phenolic resin fluid permeates in to the dentinal-tubule and set in it. The permeability of this agent was also able to permeate into intercellular substance and changed the appearance of inter-weaved fibril to the condition of agent had set. According to the Fracture Mechanics, it was not beneficial to resist the fracture progress if the microspace had been fulfilled by the agent. The tensile stress of resinified dentin was 387 kg/cm2, which was 30 kg/cm2 lower than that of unresinified-dentin.

Dentin↗
PubMed1990

[Studies on the low skin impedance points and the feature of its distribution along the channels by microcomputer. I. Observation on the reliability of the measurement].

According to the requirement of channel research, a system for the measurement of skin impedance had been designed and a series of experiments to check the reliability of this system had also been done. The facts demonstrated that the pressure exerted by the exploring electrode, the duration of switch-on as well as the number of times of repeated measurements all showed no conspicuous influences on the skin impedance. The results are stable and reliable. Moreover, the measurement and data processing are controlled by microcomputer. Thus, the method of measurement of skin impedance along the channels has been developed to a higher level. Under the conditions of our experiment, the impedance of the low skin impedance points (LSIPs) are about 108k omega, which are quite low than that of the non-LSIPs around them. The difference between the two is highly significant. Both the impedance of LSIPs and non-LSIPs are stable, without marked variation. These results provide the prerequisites indispensable for the further observation on the feature of the distribution of LSIPs.

Acupuncture Points↗
PubMed1990

[Studies on nutrition source of seeds germination of gastrodia elata B1].

The seeds of Gastrodia elata lack an endosperm and other stored nutrition and thus do not easily germinate. Armillaria mellea inhibit germination of the seeds, which exist in a type of symbiotic relationship with fungi. The nutrition necessary for germination is derived from Mycena osmundicola invading cells of the embryo. The tree leaves provide a good medium for Mycena osmundicola growth and an indirect nutritional source for germination.

Agaricales↗