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Biomedical subjects

T Ohta

Publications and source records attributed to T Ohta.

At least 1,405 records · Page 78Linked to original sources
PubMed1977

Relationship between phospholipid compositions and transport activities of amino acids in Escherichia coli membrane vesicles.

Cells of Escherichia coli were incubated in broth medium in the presence of 5 mM of hydroxylamine which completely inhibited growth but did not affect viabilities. Hydroxylamine is known to inhibit phosphatidylserine decarboxylase. A large amount of phosphatidylserine (up to 20% of total phospholipids), which did not occur in normal cells, accumulated accompanied with a decrease in phosphatidylethanolamine. Higher uptake activities of serine and glutamate were observed with the hydroxylamine-treated cells than control cells. When membrane vesicles from hydroxylamine-treated cells were prepared, they also displayed higher uptake activities of serine, proline, glutamate, and threonine than those of normal membranes. When hydroxylamine-treated cells were incubated with chloramphenicol, at concentrations which almost completely inhibited protein synthesis, the composition of phosphatidylserine decreased with a concomitant increase in that of phosphatidylethanolamine. The phospholipid composition of these cells incubated for 5 h with chloramphenicol became almost normal. Membranes vesicles prepared from such cells displayed reduced uptake activities, which were close to those of normal vesicles. These results were interpreted as indicating the altered transport activities due to the altered phospholipid composition.

Amino Acids↗
PubMed1977

Cerebrovascular sensitivity to vasoconstricting agents induced by subarachnoid hemorrhage and vasospasm in dogs.

In anesthetized dogs, subarachnoid hemorrhage (SAH) was induced by the mechanical rupture of the unilateral intracranial internal carotid artery. Vasospasm was angiographically determined 24 hours and 7 days after SAH. Contractile responses to serotonin, norepinephrine, histamine, and K+ were compared in control and bleeding sides of the middle cerebral arteries removed from dogs with SAH, and from sham-operated dogs. Under sham operation and 2 hours after SAH, responses in the arteries of both sides did not appreciably differ but response was significantly less in arteries from the bleeding side as compared with the control side 24 hours and 7 days after hemorrhage. However, median effective concentrations of serotonin, histamine, and K+ were approximately the same in arteries from both sides. Vasospasm and decreased sensitivity to the vasoactive agents of middle cerebral arteries were reversed 42 days after SAH. It is thus quite likely that initiation and maintenance of post-hemorrhage vasospasm is not associated with an increase in the sensitivity of cerebral arteries to vasconstricting endogenous substances, rather the state of decreased sensitivity of cerebral arteries in contact with SAH may be instrumental in relieving prolonged vasospasm.

Animals↗
PubMed1976

Discovery of insect anti-juvenile hormones in plants.?2U.

Two simple chromenes with anti-JH activity have been isolated and identified from the bedding plant Ageratum houstoianum. By contact and fumigation these compounds induce precocious metamorphosis and sterilization in several hemipteran species of insects. Certain holometabolous species are sterilized, forced into diapause, or both. Each of these biological actions is equivalent to removal of the corpora allata, which produce the JH's, and is reversible by treatment with exogenous JH. Thus, the action of these compounds is to stop the production or depress the titer of the JH's. To our knowledge, this is the first discovery of anti-JH, and we hope it will guide the way to the emergence of a fourth generation of safe and insect-specific pesticides.

Female↗
PubMed1976

Simulation studies on the evolution of amino acid sequences.

A model of molecular evolution in which the parameter (intrinsic rate of amino acid substitution) fluctuates from time to time was investigated by simulating the process. It was found that the usual method of estimation such as Poisson fitting underestimates this variation of the parameter when remote comparisons are made. At the same time, four distance measures (minimun base difference, Poisson fitting, random nucleotide substitutions and negative binomial fitting) were tested for their accuracy. When the substitution rate is not uniform among the amino acid sites, the negative bionomial fitting gives most satisfactory results, however, one needs to know the parameter beforehand in order to use this method. It was pointed out that the fluctuation of the evolutionary rate is expected if the nearly neutral but very slightly deleterious mutations play an important role on molecular evolution.

Amino Acid Sequence↗
PubMed1976

Beta-3-Oxindolylalanine: The main intermediate in tryptophan degradation occurring in acid hydrolysis of protein.

Under hydrolytic conditions using 6 M HCl, tryptophan reacted separately with dithiodiglycolic acid and cystine to give beta-3-oxindolylalanine (beta-[3-(2-indolinone)]alanine) as the main product. A compound, which eluted in the amino acid analyzer at the same position as beta-3-oxindolylalanine, was found in the acid hydrolyzate of lysozyme. The identicalness of these two compounds was established by comparison of their ultraviolet absorption spectra, elution positions on ion exchange chromatograms, etc. The "acid degradation product of tryptophan", which is known to be produced upon acid hydrolysis of tryptophan-containing proteins, must also be the same compound.

Chromatography, Ion Exchange↗
PubMed1976

Cleavage initiation activities of microtubules and in vitro reassembled tubulins of sperm flagella.

Cleavage of fish (Oryzias latipes) eggs was induced by injection of heterologous (sea urchin Hemicentrotus pulcherrimus and oyster Crassostrea gigas) sperm microtubules. Cleavage initiating CI activity of microtubules was higher in 3% PVP suspension than in 6% BSA, and not affected significantly by the concentration of microtubules themselves. The CI activity of microtubules suspended in 3% PVP was comparatively stable in the frozen state. Heat-treatment at more than 55 degrees C resulted in the loss of most or all of their CI activity. Such activity was observed in side-by-side aggregates of tubulin linear polymers of sea urchin (Hemicentrotus pulcherrimus) spermatozoa but not in dispersed linear polymers or tubulin dimers. Microtubules with CI activity seem to participate in initiating cleavage as astral centers, or a "seed" for polymerization of ooplasmic tubulins in activated eggs.

Animals↗
PubMed1976

Fluorometric investigation of the local conformation of 16S rRNA in the regions of the 3'- and 5'-ends.

The conformational changes of ribonucleic acid induced by heat treatment were studied by measurements of fluorescence polarization, circular dichroism, and ultraviolet absorption. The fluorescence polarization of proflavine covalently bound to the 3'-end of 16S ribosomal RNA of Escherichia coli and that of ethenoadenosine conjugated to the 5'-end of the RNA indicated that a conformational difference existed between heat-treated and untreated samples of the RNA in the regions near the 3'- and 5'-ends. Comparison of the fluorescence polarization data with other optical measurements indicated that the local conformation around the 3'- and 5'-ends of the RNA was converted to a more rigid and stable form by the heat treatment, while the gross conformation did not appear to change.

Adenosine↗
PubMed1976

Dopamine-beta-hydroxylase activity in serum and cerebrospinal fluid in neuropsychiatric diseases.

A 24-hour rhythm in serum dopamine-beta-hydroxylase (DBH) activity in chronic schizophrenic patients showed a similar change as that in normal subjects: the highest activity during day time with a peak at 12.00 h and the lowest activity at night with a bottom at 24.00 hr, 4 h after sleep onset. Between a group of schizophrenic patients who have sleep disturbance and another group of patients who have normal sleep patterns, no significant difference was observed in the 24-hour rhythm in serum DBH activity. Very low but significant DBH activity was found in cerebrospinal fluid of neuropsychiatric patients, and the values were approximately 1/1,000 of the serum activity. A case after cerebral injury showed a high DBH activity in cerebrospinal fluid.

Chronic Disease↗