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Biomedical subjects

H Seto

Publications and source records attributed to H Seto.

At least 415 records · Page 23Linked to original sources
PubMed1977

Clinical comparison of 99mTc-labeled preformed phytate colloid and sulfur colloid: concise communication.

An in vitro preformed colloid preparation of 99mTc-Sn-phytate was compared both qualitatively and quantitatively with a commercial 99mTc-sulfur colloid kit in 30 patients. The degree of liver and spleen deposition of radiocolloid was, for practical purposes, the same. A slightly higher background was visually noted in 33% of the patients receiving preformed colloidal 99mTc-Sn-phytate, but it did not interfere with the diagnostic quality of the liver and spleen images. The only advantage of the phytate compound was a preparation time of less than 5 min.

Colloids↗
PubMed1976

Effect of methylmercury on humoral immune responses in mice under conditions simulated to practical situations.

A suppression and delay in reaching the peak of primary humoral response in mice was noted when relatively large dosage of methylmercury was administered in a short time period, suggesting the interference with the initial multiplications of antibody producing cells. On the other hand, subchronic administration of low levels of methylmercury in diet (0.5 and 5ppm) caused no definite suppression on either primary or secondary responses, though they tended to be depressed.

Age Factors↗
PubMed1976

Calcium-requiring step in the uptake of deoxyribonucleic acid molecules through the surface of competent pneumococci.

The conversion of surface-adsorbed deoxyribonucleic acid (DNA) molecules to a state in which they are inaccessible to exogenous deoxyribonuclease requires specifically calcium ions; magnesium ions cannot replace calcium ions. Virtually maximal levels of nuclease-resistant DNA binding and genetic transformation can be obtained in media free from magnesium and containing only calcium ions. It is suggested that the calcium-requiring process is the transport of DNA molecules across the plasma membrane. Magnesium ions stimulate both the loss of surface-adsorbed DNA to the medium and the extracellular degradation of DNA.

Calcium↗
PubMed1975

Protoplast formation and leakage of intramembrane cell components: induction by the competence activator substance of pneumococci.

Treatment of pneumococci with activator (a protein that induces bacterial "competence" to absorb deoxyribonucleic acid molecules and undergo genetic transformation) can cause either protoplast formation or leakage of intracellular components to the medium depending on postincubation conditions. The leaked intracellular components include nucleoside phosphates, beta-galactosidase, deoxyribonuclease, autolysin, and hemolysin. Leakage and protoplast formation are induced by the electrophoretically pure activator, and these phenomena require the same conditions as induction of competence for genetic transformation, namely, genetic capacity for competence, protein synthesis, incorporation of choline, and the optimal pH for activation. It is suggested that the activator protein accelerates a normal process of transport (leakage) of autolysin molecules into the periplasmic space. The activity of these autolysin molecules from within would then unmask deoxyribonucleic acid binding sites located on the plasma membrane.

Bacterial Proteins↗
PubMed1975

Two types of glucose effects on beta-galactosidase synthesis in a membrane fraction of Escherichia coli: correlation with repression observed in intact cells.

A membrane fraction obtained from an osmotic lysate of Escherichia coli spheroplasts retains capability to synthesize beta-galactosidase. The system also retains cellular regulatory functions, one of which is known as catabolite repression. Two types of repression of beta-galactosidase synthesis were observed in this membrane system: one was caused by the addition of 2-deoxyglucose or glucose at a low concentration (3 times 10- minus 4 M), and the other was caused by glucose-6-phosphate or glucose at a high concentration (3 times 10- minus 2 M). In the presence of cyclic adenosine 3',5'-monophosphate (10 mM), repression caused by the former was completely reversed, whereas repression by the latter was only partially reversed. Conditions in intact cells causing transient and permanent repression were also investigated. Upon addition of 2-deoxyglucose or glucose at a low concentration to intact cells, only transient repression of beta-galactosidase synthesis was observed. Glucose at a high concentration caused both transient and subsequent permanent repression, and intensity of permanent repression depended upon glucose concentration, whereas duration and intensity of transient repression were independent of glucose concentration. Mutants deficient in phosphoenolpyruvate-phosphotransferase system (Hpr minus and enzyme I minus) showed transient repression but failed to show permanent repression. In mutants deficient in glucose catabolism beyond glucose-6-phosphate, both transient and permanent repression were observed. Correlation between the observations in the membrane system and in intact cells is discussed. The results obtained here strongly suggest that transient repression is caused by glucose itself, and that permanent repression is caused by glucose-6-phosphate of high intracellular levels of glucose.

Cell Fractionation↗
PubMed1975

Effect of glucose and its analogues on the accumulation and release of cyclic adenosine 3',5'-monophosphate in a membrane fraction of Escherichia coli: relation to beta-galactosidase synthesis.

Correlation between beta-galactosidase synthesis and cyclic adenosine 3',5'-monophosphate (cAMP) levels in a membrane fraction obtained from disrupted spheroplasts of Escherichia coli was investigated. Repression of beta-galactosidase synthesis in the membrane fraction by glucose-6-phosphate and by 2-deoxyglucose differed in sensitivity to reversal by cAMP. The difference between the two repressions could be due to the fact that glucose-6-phosphate inhibited severely the accumulation of exogenous [3-H]cAMP by the membrane fraction, whereas 2-deoxyglucose had little effect on the accumulation of the nucleotide. On the other hand, a quick decrease in the level of [3-H]cAMP preaccumulated in the membrane fraction resulted from addition of either glucose-6-phosphate or 2-deoxyglucose. Results reported here suggest that repression of beta-galactosidase synthesis is associated with anabrupt decrease in cAMP levels at the intramembranal sites where beta-galactosidase is synthesized, and the major, if not sole, mechanism which leads to instantaneous drop of cAMP level is via the release of cAMP, but not by degradation of the nucleotide since the membrane fraction retained less than 10 percent of cellular cyclic phosphodiesterase and the activity of the enzyme was not affected by repressing sugars.

Adenylyl Cyclases↗
PubMed1975

Nucleolytic degradation of homologous and heterologous deoxyribonucleic acid molecules at the surface of competent pneumococci.

Competent pneumococci can catalyze the rapid and quantitative degradation of extracellular deocyribonucleic acid (DNA) molecules through the activity of surface-located nucleases (endo- and, possibly, exonucleases as well). Both homologous and heterologous DNAs are degraded by a mechanism that seems to involve a cyclic process: (i) attachment of DNA to the cell surface followed by (ii) nucleolytic attack, and (iii) release to the medium. Processes (ii) and (iii) are both inhibited by ethylenediaminetetraacetate. Whereas surface nuclease activity is specific for competent cells, the bulk of this activity is not coupled to irreversible DNA uptake (deoxyribonuclease-resistant binding). Pneumococcal DNA treated with ultraviolet irradiation or nitrous acid (cross-linking?) is selectively impaired in the ability to irreversibly bind to competent cells, whereas reversible binding is normal.

Adenoviridae↗
PubMed1975

Cell surface-located deoxyribonucleic acid receptors in transformable pneumococci.

We studied deoxyribonucleic acid (DNA) binding in transformable pneumococci. The relevant findings are as follows. (i) At least half of the DNA Molecules adsorbed to competent cells in the growth medium are attached to sites on the protoplast membrane. (ii) Most of the DNA bound to live competent cells in the presence of glucose is not released by moderate shear or by autolysin treatment. In contrast, most of the DNA adsorbed to competent cells in the absence of glucose is shear and autolysin sensitive. (iii) The presence of binding sites resembling in properties the sites in live competent cells can be demonstrated in wall-membrane complexes. Most of these sites are lost during preparation of cell walls and protoplasts. It is suggested that the DNA-binding site is a membrane component (protein?) Stabilized by polysaccharide (cell Wall) material. (IV) Mechanical or enzymatic damage to the cell wall or change in the ionic conditions can induce DNA binding (and surface-nuclease activity) in the incompetent pneumococci. However, such cells still show neither genetic transformation nor extensive nuclease-resistant binding of DNA. It is suggested that both competent and incompetent cells contain a large number of sequestered DNA-binding sites that can be unmasked by several experimental conditions. Induction of the competent state by the competence activator protein may involve an endogenous unmasking process.

Binding Sites↗
PubMed1975

Selective release of a deoxyribonucleic acid-binding factor from the surface of competent pneumococci.

Methods are described that resulted in the selective release of deoxyribonucleic acid (DNA)-binding factor from the surface of competent pneumococci. The same methods caused a parallel inactivation of the DNA-binding capacity of the extracted bacteria. Genetically or physiologically incompetent pneumococci did not yield binding factor upon exposure to the same methods. The solubilized binding factor appeared to be a protein; it could be assayed by a membrane filter binding procedure. The binding factor had properties reminiscent of those of the DNA receptors of transformable pneumococci (Seto et al., 1975).

Bacterial Proteins↗
PubMed1975

Isolation and purification of blasticidin S deaminase from Aspergillus terreus.

An enzyme catalyzing the deamination of the cytosine moiety of blasticidin S was extracted from a fungal strain that belongs to Aspergillus terreus. The enzyme was purified with ammonium sulfate fractionation, Sephadex G-100 column and DEAE cellulose column chromatography, followed by preparative polyacrylamide gel electrophoresis. Blasticidin S deaminase could be separated easily from co-existing cytidine deaminase by DEAE column chromatography or gel electrophoresis, and preliminary study on the substrate specificity showed that this enzyme acts on blasticidin S derivatives, such as cytomycin and acetylblasticidin S, but not on cytosine, cytidine, purine bases or their nucleosides. Blasticidin S deaminase could be induced by the addition of blasticidin S to the culture, and sulfhydryl compounds, such as mercaptoethanol, were effective in protecting the enzyme from inactivation. The homogeneity of the enzyme was examined by both sedimentation analysis and polyacrylamide gel electrophoresis. The molecular weight and isoelectric point were found to be around 30,000 and 4.35, respectively. Some other properties were also examined.

Aminohydrolases↗