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Biomedical subjects

S Nishimura

Publications and source records attributed to S Nishimura.

At least 883 records · Page 49Linked to original sources
PubMed1981

Effect of methyl substitution on mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline, isolated from broiled sardine.

2-Amino-3-methylimidazo[4,5-f]quinoline [I] is a potent mutagen isolated from broiled sun-dried sardine. [I] and its seven of derivatives, (two isomers, one demethylated derivative and four methyl-substituted derivatives), were tested for mutagenicity on Salmonella typhimurium TA98 and TA100 in the presence of S9 mix. 2-Amino-1,4-dimethylimidazo[4,5-f]quinoline was the strongest mutagen of these 8 compounds on TA98, giving 159,000 revertants/nmol (750,000 revertants/micrograms). The demethylated derivative, 2-aminoimidazo[4,5-f]-quinoline, had very weak mutagenicity, inducing only 55 revertants/nmol (200 revertants/micrograms). Compounds having a methyl group at position N-1 or N-3 of 2-aminoimidazo[4,5]f]quinoline were strong mutagens. The 1,5-dimethy-derivative was more mutagenic than 3,5-dimethyl-derivative. Introduction of a methyl group at position 4 and position 5 enhanced and reduced the mutagenicity, respectively. All the compounds tested were more mutagenic to TA98 than to TA100, but their relative orders of mutgenicity with TA98 and TA100 were the same.

Animals↗
PubMed1981

Biological and structural differences between tRNAVal species isolated from rat ascites hepatoma cells and normal rat liver.

On RPC-5 column chromatography, the main valine acceptor activity of tRNA (tRNA2Val) from rat ascites hepatoma cells was eluted later than that of normal rat liver tRNA (tRNA1Val). The tRNA2Val was aminoacylated by E. coli amino-acyl-tRNA synthetase, while tRNA1Val from normal rat liver was not. Rat fetal liver tRNAVal was also aminoacylated by E. coli aminoacyl-tRNA synthetase. tRNA1Val (rat liver) and tRNA2Val (ascites hepatoma) were each purified to a homogeneous state by RPC-5 column chromatography and two-dimensional polyacrylamide gel electrophoresis, and their sequences were determined by post-labeling techniques. Ascites hepatoma tRNA2Val differed from rat liver tRNA1Val in that Gm18, C32 and an unknown modified nucleoside, N34, in the latter tRNA were mostly replaced by G, Cm, and inosine, respectively. In addition, 3'-terminal adenosine was not present in tRNA1Val (normal rat liver), but was in tRNA2Val (ascites hepatoma). Other modifications and the primary structures of the two tRNAValS were found to be the same. Thus it was concluded that the new iso-acceptor species of tRNA Val in ascites hepatoma cells is due to a change of post-transcriptional modification, not to a change of tRNA transcription. The unique feature of the change of post-transcriptional modification in tRNA2Val (ascites hepatoma) is that both hypo- and hyper-modification take place simultaneously in the tRNA molecule depending the locations of nucleotide residues.

Amino Acids↗
PubMed1981

Changes in amount of hypo-modified tRNA having guanine in place of queuine during erythroid differentiation of murine erythroleukemia cells.

The amounts of hypo-modified tRNAs having guanine in place of queuine in murine erythroleukemic cells decreased markedly when the cells differentiated into mature erythroid cells. The amounts of these hypo-modified tRNAs can be determined easily by measuring incorporation of labeled guanine into tRNA with Escherichia coli tRNA--guanine transglycosylase. The decrease was detected at on early stage of erythroid differentiation: namely, before any detectable increase in the percentage of cells containing hemoglobin. The amount of guanine-accepting tRNA species was nearly proportional to the percentage of undifferentiated cells in the population, regardless of the type of inducer used. Decrease in the amounts of hypo-modified tRNAs in the cells was effectively blocked by 12-O-tetradecanoylphorbol 13-acetate, which inhibits differentiation of these cells. 8-Azaguanine, which is known to be substrate of tRNA--guanine transglycosylase, was incorporated almost exclusively into the first position of hypo-modified tRNA in murine erythroleukemic cells when they were pulse-labeled in culture with 8-azaguanine, suggesting strongly that tRNA-guanine transglycosylase in the cells is actually involved in incorporation of 8-azaguanine into tRNA in vivo. The amount of 8-azaguanine incorporated into tRNA in differentiated cells was one third of that in undifferentiated cells, the decrease being parallel with that in the amount of guanine-accepting tRNA in these cells. The results suggest that the appearance of hypo-modified tRNAs in the transformed cells was due to lack of substrate for queuosine biosynthesis in tRNA.

Animals↗
PubMed1981

Exocytotic secretion of catecholamines from the cat adrenal medulla by sodium deprivation: involvement of calcium influx mechanism.

1 Cat adrenal glands were perfused with Ca-deficient medium and secretion of catecholamines (CA) was induced by perfusion with Na-free medium in which NaCl was replaced by an osmotically equivalent amount of sucrose. 2 Release of CA and dopamine-beta-hydroxylase (DBH), but not that of phenylethanolamine-N-methyltransferase, was concomitantly found in the effluents when the adrenals were stimulated, indicating that secretion was due to exocytosis. 3 Secretion of CA induced by Na-free (sucrose) medium was dependent on the concentration of Ca and was saturated at 0.5 mM of Ca. 4 Sr or Ba substituted for Ca in maintaining secretion by Na-free (sucrose) medium. 5 The addition of Na, Li or alkali metal ions to Na-free (sucrose) medium containing Ca reduced the response to a variable extent but this inhibition was reversed by raising the concentration of Ca in the Na-free medium. 6 All of the Na substitutes used induced secretion only when this medium contained Ca. However, different Na substitutes released different amounts of CA; sucrose was most effective, K, Tris and choline were moderately and Li least effective. 7 Secretion of CA by Na-free (sucrose) medium was strongly inhibited by D-600, tetracaine or divalent cations such as Co, Ni, Zn and Mg. The inhibition by Co was partially reversed by raising the concentration of Ca in the Na-free medium. 8 Secretion of CA from bovine isolated chromaffin cells was induced by Na-deficient (sucrose) medium and was dependent on the concentrations of ionized Ca involved. 9 All the Na substitutes tested increased secretion of CA and 45Ca uptake, in a parallel fashion. 10 A correlation between secretion and 45Ca uptake was found under various experimental manipulations which reduced secretion of CA. 11 These results demonstrated that unlike the perfused bovine adrenals, the Ca influx mechanism is essential for secretion by Na deprivation in the perfused cat adrenals as it is in bovine isolated chromaffin cells. 12 It is suggested that Na deprivation increases Ca entry through the Ca channels by eliminating the competition between Na and Ca, and possibly by activating Ca influx linked with Na efflux.

Adrenal Medulla↗
PubMed1981

[Cranial computed tomography of the neurofibromatosis (author's transl)].

The computed tomography (CT) was performed in 10 cases of neurofibromatosis. The CT scan showed the abnormal findings in 8 cases out of 10. Skull lesions were noted in 3 cases and intracranial tumors were found in 5 among which multiple neoplasms were seen in 3. Although reported cases were not large enough in number, the incidence and variety of the tumors were similar to others reported before CT era.

Adolescent↗