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Biomedical subjects

G Eguchi

Publications and source records attributed to G Eguchi.

At least 109 records · Page 6Linked to original sources
PubMed1981

Carcinogens on regeneration. Effects of N-methyl-N'-nitro-N-nitrosoguanidine and 4-nitroquinoline-1-oxide on limb regeneration in adult newts.

A microcrystal (ca 5 micrograms) of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or 4-nitroquinoline-1-oxide (4NQO) was directly administered to the regeneration blastema on day 7 after amputation of a forelimb in the newt in order to analyze the effect of such potent carcinogenic substances on regeneration cells. Although neither MNNG nor 4NQO arrested regeneration completely, they caused great retardation of the regeneration cone formation followed by various abnormalities in the bony structures. Abnormal regenerants could be classified into the following four categories; (1) complete absence of both ulna and radius; (2) subregeneration or superregeneration of carpals and digits; (3) multiple disorganization of skeletal elements; (4) arrest of regeneration at the stage of regeneration cone. The polarity of regenerants developed after application of MNNG or 4NQO was very often shifted, during which the regeneration cone was always formed from the site where a microcrystal of the carcinogens was administered. The secondary regeneration initiated by reamputation of the regenerating limb, which had received the carcinogens at the early blastema stage, proceeded in the same way as observed in the case of a simple amputation. This suggested local and temporal effects of the carcinogens applied. Nevertheless, tumor formation has not induced in the newt limb so far. We can learn from these data that both MNNG and 4NQO only alter behavior of the newt regeneration cells without excreting their carcinogenic effects on them, and that the newt cells are highly resistant and stable against the above-mentioned carcinogens.

4-Nitroquinoline-1-oxide↗
PubMed1979

Disappearance of calcium-induced phase separation in phosphatidylserine-phosphatidylcholine membranes caused by protonation and by electric current.

Disappearance of Ca2+-induced phase separation in phosphatidylserine-phosphatidylcholine membrane has been studied under several conditions by monitoring electron spin resonance spectrum of spin-labeled phosphatidylcholine. The membranes were prepared in Millipore filters. Electron micrographs of the pre parations showed formation of multilayered structures lined on the pore surface. The phase separation was disappeared when the membrane was soaked in non-buffered salt solution (100 ml KCl, pH 5.5). It was markedly contrasting that when the bathing salt solution was buffered no disappearance was observed. Disappearance of the phase separation was also observed when the Ca2+-treated membrane was transferred to acidic salt solutions (less than or equal to pH 2.5) or to low ionic strength media (less than or equal to mM) buffered at pH 5.5, and then to the buffered salt solution (100 mM KCl, pH 5.5). These are due to replacement of Ca2+ by proton, proton-induced separation, followed by disappearance of the phase separation in the buffered salt solution. Biological significance of the competition between Ca2+ and proton for the phase separation or domain formation in the membranes was emphasized.

Calcium↗
PubMed1977

Studies on aspartase. IV. Reversible denaturation of Escherichia coli aspartase.

Aspartase (L-aspartate ammonia lyase, EC 4.3.1.1) of Escherichia coli, denatured in 4 M guanidine-HCl, was renatured in vitro by simple dilution with a concomitant restoration of the activity. While the native enzyme exhibited a marked negative Cotton effect centered at 233 +/- 1 nm in optical rotatory dispersion, the enzyme denatured in 4 M guanidine-HCl retained little optical activity. Upon dilution of the denatured enzyme, however, more than 90% of the ordered structure was recovered in 1 min, while the restoration of the activity proceeded much more slowly. Estimation of molecular weights by gel permeation chromatography indicated that the tetrameric enzyme is subject to reversible dissociation into monomeric subunits under the experimental conditions. Various environmental factors such as temperature, pH and protein concentration exhibited profound influence on the rate and extent of the reactivation. In order to examine the correlation between the restoration of the activity and the quaternary structure, electron microscopic inspection of the kinetic processes of reversible denaturation was attempted. Upon dilution of the denatured enzyme at 4 degrees C, neither the activity nor tetrameric images were detected over several min. Upon the temperature shift up to 25 degrees C, however, the activity regain was rapidly proceeded concomitant with the appearance of tetrameric molecules. These results are compatible with the possibility that the subunit assembly is an essential prerequisite, thought not sufficient, for enzyme activity.

Ammonia-Lyases↗
PubMed1976

Abnormalities in the differentiation and cellular properties of hyperplastic lens epithelium from strains of chickens selected for high growth rate.

Similar morphological abnormalities of the lens of the eye of two unrelated strains of chicks, both of which had been selected for high growth rate, were found to be associated with epithelial cells showing marked deviations from the normal in cell surface properties, mitotic rate, capacity for differentiation, and in DNA, RNA and protein metabolism. The relationship between these modified properties and the observed morphology is discussed.

Animals↗
PubMed1974

Differentiation of lens-like structures from newt iris epithelial cells in vitro.

Dissociated cells of pigmented iris epithelium from adult newts grew intensively in monolayer cultures after a lag of two to three weeks. During the lag period, depigmentation occurred in many cells. When cultures became confluent five to six weeks after seeding, many tiny lens-like structures (30-70 per plate) differentiated from dense foci of amelanotic epithelial cells. These lens-like structures appeared in all cultures originated from cells of ventral as well as dorsal iris. The identification of these structures as lens was established by both immunological and ultrastructural techniques.

Animals↗
PubMed1973

Differentiation of lens tissue from the progeny of chick retinal pigment cells cultured in vitro: a demonstration of a switch of cell types in clonal cell culture.

Clonal cell lines isolated from the pigmented retina of 8.5-day chick embryos initially retained the capacity to form pigment. After several passages, however, many cells lost pigment granules and differentiated into lens-like structures. The lens-specific nature of the structures formed in cultures originally derived from retinal pigment cells was established by both ultrastructural and immunological studies.

Animals↗