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Biomedical subjects

M Mitani

Publications and source records attributed to M Mitani.

At least 109 records · Page 6Linked to original sources
PubMed1977

Studies on the ionophorous antibiotics. VIII. Effects of monovalent and divalent cation ionophores on blood platelets.

The effects of a monovalent cation ionophore etheromycin (CP-38295) and a divalent cation ionophore lysocellin on blood platelets function have been investigated. When platelets were incubated with 3 micronM of each ionophore, the simultaneous induction of secretion of stored serotonin and efflux of intracellular calcium occurred, but there was no detectable influx of extracellular calcium. With increasing concentrations, these compounds caused platelet aggregation accompanied by increased influx of external calcium. These results are consistent with the hypothesis that the liberation of calcium from the intracellular store mediated the platelet secretion reaction.

Animals↗
PubMed1977

Studies on the ionophorous antibiotics. XII. Effects of ionophore lysocellin on cation distribution and respiration in mitochondria.

The effects of the ionophore lysocellin on the movements of Ca2+, Mg2+ and alkali metal cations and its effect on energy utilization by rat liver mitochondria have been investigated. At a concentration of 0.05 micrometer, lysocellin induced dissociation of membrane-bound calcium, and an apparent steady state was established across the inner membrane between energy-linked calcium accumulation and the ionophore-induced depletion of calcium. No detectable efflux of intramitochondrial Ca2+ and Mg2+ was induced by 0.05 micrometer lysocellin, but the uptake of exogenously added calcium was significantly inhibited. The ionophore augmented Mg2+ release from mitochondria induced by Ca2+ addition and also caused rapid release of K+ from mitochondria preloaded with K+ by valinomycin or monazomycin. High levels (0.5 approximately 10 micrometer of lysocellin caused massive depletion of endogenous Ca2+, Mg2+ and K+ from mitochondria, resulting in disruption of mitochondrial functions including release of state 4 respiration, stimulation of ATPase and inhibition of ADP- or DNP-stimulated respiration. Structure-activity studies with chemically modified compounds of lysocellin indicated the important role of terminal carboxylic acid and C21 hydroxyl function in the activity of the ionophore, and there is a good correlation between the effect of lysocellin on mitochondrial cation movements and its ability to complex with cations determined in an organic solvent-water two-phase partition system.

Adenosine Triphosphatases↗
PubMed1976

Salinomycin effects on mitochondrial ion translocation and respiration.

The effects of salinomycin on alkali cation transport and membrane functions in rat liver mitochondria have been investigated. After potassium uptake, stimulated by valinomycin or monazomycin in the presence of adenosine 5'-triphosphate, salinomycin caused rapid release of K(+) from mitochondria. Salinomycin reversed valinomycin- or monazomycin-induced oscillatory swelling of mitochondria preloaded with K(+), Rb(+), and Na(+) but was without effect on Li(+) or Cs(+) preloaded mitochondria. Salinomycin blocked the retention of K(+) more effectively than the retention of Rb(+) or Na(+). Salinomycin inhibited both coupled and uncoupled respiration with strict substrate specificity in medium of low but not in high K(+) concentration. The oxidation of glutamate, alpha-ketoglutarate, and malate plus pyruvate was inhibited by salinomycin, but that of beta-hydroxybutyrate or succinate was not significantly affected. Salinomycin inhibited adenosine triphosphatase activity of mitochondria induced by valinomycin or monazomycin in K(+) and Rb(+) medium without significantly affecting adenosine triphosphatase activity in Li(+), Na(+), or Cs(+) medium. Oxidative phosphorylation in mitochondria was inhibited by salinomycin but the inhibitory effect of salinomycin lacked the substrate specificity observed for respiration. It is proposed that salinomycin perturbs mitochondrial functions by acting as a mobile carrier for alkali cations through membranes.

Adenosine Triphosphatases↗
PubMed1970

Molecular recombination between R-factor deoxyribonucleic acid molecules in Escherichia coli host cells.

THREE PREVIOUSLY STUDIED R FACTORS WERE USED: 222/R4, controlling transmissible resistance to sulfonamide, streptomycin, chloromycetin, and tetracycline (SU(r) SM(r) CM(r) TC(r)); 222/R3, a derivative of 222/R4 (now termed 222/R3W) having lost TC(r); and R15, controlling infectious resistance to SU and SM only. Two types of derivative R factors were isolated from 222/R4 by serial subculture in Salmonella species. One derivative, termed 222/R1, lost resistance to SU, SM, and CM, and the other, termed 222/R3N, lost only TC(r). Each factor was transferred to a standard Escherichia coli K-12 host. Recombinant factors of 222/R4 phenotype were isolated by selection after mixed culture of E. coli (222/R1)(+) and (222/R3N)(+) strains. Density-gradient equilibrium centrifugation of lysates of E. coli R(+) hosts in the presence of ethidium bromide separated R-factor deoxyribonucleic acid (DNA) as a heavy satellite peak which was subjected to electron microscopy or analytical density gradient centrifugation. Each DNA comprised a unimolecular species of circular DNA. The contour of R15 measured 22.3 mum [equivalent to 46 x 10(6) atomic mass units (AMU)], and that of 222/R4 measured 33.6 mum (70 x 10(6) AMU). 222/R3W appeared to be a point mutant or small deletion of 222/R4 with an almost identical size, whereas 222/R3N had lost a DNA segment of about 3 mum, and measured 30.3 mum or 63 x 10(6) AMU. The 222/R1 factors also appeared to have arisen by loss of DNA from 222/R4, 222/R1A being 22.3 mum or 46 x 10(6) AMU, whereas all other 222/R1 factors appeared to be duplicates, measuring 25.6 mum or 53 x 10(6) AMU. The DNA from six recombinant factors of R4 phenotype was indistinguishable in size and configuration from the parental 222/R4. In most cases, the number of R-factor copies (present as covalently closed circular molecules) per copy of the E. coli chromosome was less than 2, ranging from 1.2 to 3.3.

Centrifugation, Density Gradient↗
PubMed1970

Circular R-factor molecules controlling penicillinase synthesis, replicating in Escherichia coli under either relaxed or stringent control.

Two infectious drug-resistance (R) factors, R28K and R6K, each conferring resistance to a number of penicillins by the synthesis of a penicillinase, were transferred to Proteus mirabilis PM1 and Escherichia coli RC85 host strains. Deoxyribonucleic acid (DNA) extracted from these strains was separated by density-gradient centrifugation and subjected to electron microscopy by use of a modification of the protein-monolayer diffusion technique. Analytical density-gradient centrifugation of the purified DNA from PM1 strains showed, in addition to the major peak at a density of 1.698 g/cm(3) characteristic of Proteus chromosomal DNA, a single satellite band at a density of 1.710 g/cm(3) [guanine plus cytosine (GC) base ratio 50%] for R28K and at 1.704 g/cm(3) (GC base ratio 45%) for R6K. Direct CsCl density-gradient centrifugation of crude lysates of the E. coli (R28K)(+) strain in the presence of ethidium bromide gave rise to a sedimentation profile with a single satellite peak containing covalently closed circular (CCC) DNA molecules with a mean contour length of 21.4 mum [44 x 10(6) atomic mass units (AMU)], although a minority was 13.6 mum in length. From the size of the major class, it was estimated that there were two to three copies of the R28K factor present as CCC molecules per chromosome at various phases of cellular growth. Similar studies of the E. coli (R6K)(+) lysates showed two satellite peaks; peak I contained mostly CCC molecules of contour length 12.8 mum (26 x 10(6) AMU), and peak II, intermediate to peak I and the chromosomal peak, contained CCC molecules of a similar size, together with about equal numbers of catenated molecules, mostly dimers consisting of two interlocked monomers of 12.8 mum. A smaller number (ca. 0.1%) of higher catenanes was also seen. The number of CCC copies of the R6K factor per chromosome present in peak I was calculated as 13 at logarithmic phase and 38 at stationary phase. In peak II, a constant ratio of about one catenated dimer per chromosome was found at all phases of growth. Penicillinase assays of cultures at different phases of growth showed a correlation between the estimated number of R-factor copies present as CCC molecules and the enzyme activity per cell for both R28K and R6K.

Ampicillin↗
PubMed1969

Composite circular forms of R factor deoxyribonucleic acid molecules.

Two R factors, one (R15) conferring resistance to streptomycin and sulfonamide (SM(r)SU(r)) and the other (222/R3) to streptomycin, sulfonamide, and chloramphenicol (SM(r)SU(r)CM(r)), were transferred to a Proteus mirabilis strain, and deoxyribonucleic acid (DNA) extracted from these strains was subjected to density-gradient centrifugation. R15-DNA formed a single satellite band at a density of 1.709 g cm(-3). Electron microscopy of samples from this band showed circular molecules of one type, with a contour length of 18 mum (35 x 10(6) daltons). 222/R3-DNA formed a satellite band with three peaks at densities 1.708, 1.711 and 1.717 g cm(-3). Electron micrographs revealed circular structures from each band with contour lengths, respectively, of 29 (54 x 10(6) daltons), 36 (68 x 10(6) daltons), and 6 mum (12 x 10(6) daltons). "Supertwisted" forms of several molecular species were found. It is suggested that 222/R3 DNA comprises either a single 36-mum molecule or two individual molecules, 29 and 6 mum in length, and that this may reflect the evolutionary development of R factors.

Centrifugation, Density Gradient↗