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991.
E. Kimura Masatoshi Sasada Mitsuhiko Shionoya Tohru Koike Hiromasa Kurosaki Motoo Shiro 《Journal of biological inorganic chemistry》1997,2(1):74-82
Novel potentially five-coordinate pyridyl–pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane
(H2L) and its homologs (6-methyl and 6,6-dimethyl derivatives)] have been synthesized to study nickel(II) complexation. A purple
nickel(II) complex with a deprotonated amide (NiHL) was isolated from aqueous equimolar solution of H2L and Ni(ClO4)2. A yellow nickel(II) complex with two deprotonated amides (NiL) was crystallized from an H2O/CH3CN solution of H2L and Ni(OH)2. The X-ray crystal study of NiL showed a square-planar nickel(II) complex with the pyridyl–pendant remaining uncoordinated.
It is concluded from the visible absorption and NMR study of NiL in aqueous solution that the four-coordinate NiL is in equilibrium
with a five-coordinate square-pyramidal nickel(II) complex with the apical coordination of the pyridyl–pendant. A voltammetric
study disclosed a low nickel(II/III) redox potential of +0.29 V vs SCE for NiL at pH 9.5 and 25 °C with 0.10 M Na2SO4. The nickel(II) complex NiL absorbed an equimolar amount of O2 at pH 9.5 and 25 °C, and the O2 was activated to cleave plasmid DNA.
Received: 5 August 1996 / Accepted: 24 October 1996 相似文献
992.
993.
994.
995.
Antibacterial activities of 3-di(hydroxymethyl) amino-6[2-(5-nitro-2-furyl)vinyl]-1,2,4-triazine, (dihydroxymethyl furatrizine) were investigated using mutant strains of Escherichia coli lacking repair systems for DNA damage, i.e. polA, uvrA, uvrA, uvrC, recA, recB, recC and uvrArecA. All of the mutant strains were more sensitive to the drug than the parent sgrains, as was the case with the sensitivity to UV-irradiation. These results indicate that the drug acts lethally on sensitive bacteria by damaging their DNA, and parts of the damaged DNA are repaired by excision and recombinational repair systems. Filamentous cell formation was induced in all strains except the uvrArecA strain by sublethal concentration of the drug, as well as by UV-irradiation. It is possible that the occurrence of the short period of "unbalanced growth" induced by such DNA damaging agents leads to filament formation. In the cells of the double mutant, filament formation was induced by the drug but not by UV-irradiation, and the majority of the filamentous cells formed were multinucleated. This suggests that, in this double mutant, the drug directly reacts with the septation mechinery of the cell envelope, resulting in filament formation. This hypothesis is supported by the electron microscopic observations that septation is interrupted in the filamentous cells induced by the drug. 相似文献
996.
997.
The Ca2+ dependence of surface membrane retrieval (i.e., the process by which the excess surface membrane resulting from exocytosis is recycled to the cytoplasm of secretory cells) has been investigated in rat parotid tissue lobules first incubated for 40 min in the presence of a secretagogue drug (the β-adrenergic agonist isoprenaline) and then in the presence of the β-blocker, 1-propranolol, up to 4 h. The dynamics of the luminal surface membrane was monitored by measuring, in ultrathin sections, the length of the luminal profile of all examined acinar cells abutting to a lumen before and immediately at the end of the stimulation, as well as at various times thereafter. Such a profile doubled during isoprenaline stimulation, concomitantly with the discharge of most secretion granules. After the stimulation was blocked, the luminal profile decreased to reach values even lower than those observed in unstimulated cells. The kinetics of this reduction was apparently first-order, both in the presence and in the absence of extracellular Ca2+. However, its rate differed appreciably in these two situations: it was relatively fast (apparent
) in lobules incubated in complete medium (Ca2+ concentration, 2 mM), and much slower (apparent
) in lobules incubated in a Ca2+-free medium containing 1 mM EGTA. The slowing down of the membrane retrieval occurring in Ca2+-free conditions was rapidly reversed by reintroduction of Ca2+ into the medium. These findings indicate that the retrieval of the luminal surface membrane in parotid acinar cells is Ca2+-dependent. 相似文献
998.
The kinetic mechanisms of the 2-oxoglutarate and pyruvate dehydrogenease complexes from pig heart mitochondria were studied at pH 7.5 and 25 degrees. A three-site ping-pong mechanism for the actin of both complexes was proposed on the basis of the parallel lines obtained when 1/v was plotted against 2-oxoglutarate or pyruvate concentration for various levels of CoA and a level of NAD+ near its Michaelis constant value. Rate equations were derived from the proposed mechanism. Michaelis constants for the reactants of the 2-oxoglutarate dehydrogenase complex reaction are: 2-oxoglutarate, 0.220 mM; CoA, 0.025 mM; NAD+, 0.050 mM. Those of the pyruvate dehydrogenase complex are: pyruvate, 0.015 mM; CoA, 0.021 mM; NAD+, 0.079 mM. Product inhibition studies showed that succinyl-CoA or acetyl-CoA was competitive with respect to CoA, and NADH was competitive with respect to NAD+ in both overall reactions, and that succinyl-CoA or acetyl-CoA and NADH were uncompetitive with respect to 2-oxoglutarate or pyruvate, respectively. However, noncompetitive (rather than uncompetitive) inhibition patterns were observed for succinyl-CoA or acetyl-CoA versus NAD+ and for NADH versus CoA. These results are consistent with the proposed mechanisms. 相似文献
999.
The molar growth yields of Pseudomonas denitrificans, for nitrate, nitrite and nitrous oxide, were determined in chemostat culture under electron acceptor-limited conditions. Glutamate was used as the source of energy, carbon and nitrogen. The catabolic pattern was identical, irrespective of the terminal electron acceptors. The molar growth yields, corrected for maintenance energy, were 28-6 g/mol nitrate, 16-9 g/mol nitrite and 8-8 g/mol nitrous oxide. The energy yield, expressed on an electron basis, was proportional to the oxidation number of the nitrogen: nitrate (plus 5), nitrite (plus 3) and nitrous oxide (plus 1). It was concluded that oxidative phosphorylation occurs to a similar extent in each of the electron transport chains associated with the reduction of nitrate to nitrite, nitrite to nitrous oxide and nitrous oxide to nitrogen. 相似文献
1000.
Molecular clock of silent substitution: At least six-fold preponderance of silent changes in mitochondrial genes over those in nuclear genes 总被引:19,自引:0,他引:19
Takashi Miyata Hidenori Hayashida Reiko Kikuno Masami Hasegawa Midori Kobayashi Katsuro Koike 《Journal of molecular evolution》1982,19(1):28-35
Summary For each of eleven different types of nuclear genes, comparisons of the protein coding sequences were made between human, mouse and rat pairwisely, and the evolutionary rate of silent substitution, v
S
nucl.
, was estimated. It is shown that the v
S
nucl.
is not only very high (=5.37×10–9/site/yr), but also approximately uniform for different genes regardless of the types, which confirms our previous results (Miyata et al. 1980b). This is in sharp contrast to the rate of protein evolution which differes greatly from protein to protein. Furthermore the v
S
nucl.
is shown to be approximately constant with respect to different divergence times, at least within a short time period (75 Myr). Based on these observations, we propose a new molecular clock which has several advantages over a protein clock. Using this clock, we show that the rate of amino acid replacement in the immunoglobulin Ck gene of b4 rabbit is unexpectedly high, almost comparable to the rate of silent changes. This rate may be the highest one for protein evolution that we know so far. We further examine the rate of silent substitutions in mitochondrial genes comparing mouse and rat. Surprisingly the rate is extremely high (35×10–9/site/yr), at least 6-times as high as the corresponding rate of nuclear genes. Based on the estimate, we discuss a possible origin of the rapid rate found in mitochondrial DNA. 相似文献