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151.
Abstract Incorporation of [ methyl -3 H]thymidine into bacterial DNA was determined for a range of axenic anaerobic bacterial cultures: fermentative heterotrophs, sulphate-reducing bacteria, purple sulphur bacteria, acetogens and methanogens. Anaerobically growing Bacillus sp. and the obligate aerobe Thiobacillus ferrooxidans were also investigated. Actively growing cultures of sulphate-reducing bacteria belonging to the genera Desulfovibrio, Desulfotomaculum, Desulfobacter, Desulfobotulus and Desulfobulbus , purple sulphur bacteria ( Chromatium vinosum OP2 and Thiocapsa roseopersicina OP1), methanogens ( Methanococcus GS16 and Methanosarcina barkeri ) and an acetogen ( Acetobacterium woodii ) did not incorporate [ methyl -3 H]thymidine into DNA. The only obligate anaerobes in which thymidine incorporation into DNA could be unequivocally demonstrated were members of the genus Clostridium . Anaerobically growing Bacillus sp. also incorporated thymidine. These data demonstrate that pure culture representatives of major groups of anaerobic bacteria involved in the terminal oxidation of organic carbon and anoxygenic phototrophs within sediments are unable to incorporate [ methyl -3 H]thymidine into DNA, although some obligate and facultative anaerobes can. Variability in thymidine incorporation amongst pure culture isolates indicates that unless existing techniques can be calibrated to take this into consideration then productivity estimates in both aerobic and anaerobic environments may be greatly underestimated using the [ methyl -3 H]thymidine technique. 相似文献
152.
Ian M. Møller Allan G. Rasmusson Kenneth M. Fredlund 《Journal of bioenergetics and biomembranes》1993,25(4):377-384
Plant (and fungal) mitochondria contain multiple NAD(P)H dehydrogenases in the inner membrane all of which are connected to the respiratory chain via ubiquinone. On the outer surface, facing the intermembrane space and the cytoplasm, NADH and NADPH are oxidized by what is probably a single low-molecular-weight, nonproton-pumping, unspecific rotenone-insensitive NAD(P)H dehydrogenase. Exogenous NADH oxidation is completely dependent on the presence of free Ca2+ with aK
0.5 of about 1 µM. On the inner surface facing the matrix there are two dehydrogenases: (1) the proton-pumping rotenone-sensitive multisubunit Complex I with properties similar to those of Complex I in mammalian and fungal mitochondria. (2) a rotenone-insensitive NAD(P)H dehydrogenase with equal activity with NADH and NADPH and no proton-pumping activity. The NADPH-oxidizing activity of this enzyme is completely dependent on Ca2+ with aK
0.5 of 3 µM. The enzyme consists of a single subunit of 26 kDa and has a native size of 76 kDa, which means that it may form a trimer. 相似文献
153.
DTT(二流苏糖醇)可解除TPT(氯化三苯锡)对叶绿体光合磷酸化的抑制、减弱TPT对类囊体跨膜△pH的抑制和对类囊体腔内质子外流的促进。由于TPT较专一作用于CF0,推测CF0受DTT修饰。这从DTT可消除TPT对去除CF1的类囊体残缺膜△pH的重建和对残缺膜光下收缩的促进得到进一步的证明。DTT的作用是还原二硫键成为游离的巯基,因而CF0可能含有二硫键。从光下DTT或暗中DTT处理残缺膜对TPT作用的影响,可以看到DTT对CF0的修饰是需光的,类囊体膜在光下发生的构象变化,使CF0的二硫键暴露而被DTT修饰。CF0的二硫键较CF1γ的二硫键更快、更敏感地被DTT所修饰。 相似文献
154.
155.
Joseph H. Sellin Roland DeSoignie Susan Burlingame 《The Journal of membrane biology》1993,136(2):147-158
Short-chain fatty acids (SCFAs) are the predominant luminal anion in the mammalian colon. Although they are rapidly absorbed
in vivo, little is known about the mechanisms of transepithelial transport in vitro. Previous studies have suggested that
SCFA transport may be linked to Na absorption or an anion exchange mechanism. We compared the transport of propionate under
short-circuit conditions in rabbit proximal and distal colon to determine whether there were segmental differences, how SCFAs
may be linked to either Na absorption or anion transport, and whether SCFAs, as weak electrolytes, may be affected by transepithelial
pH gradients. In distal colon, propionate transport was not significantly altered by stimulation of electrogenic Na absorption,
epinephrine or Cl removal. However, a modest transepithelial pH gradient (luminal 6.8/serosal 7.4) stimulated propionate absorption.
In proximal colon, propionate transport was significantly altered by manuevers that either stimulated (lowered [Na] in the
bathing media) or inhibited (theophylline) apical Na−H exchange. Neither Cl removal, nor the anion exchange inhibitor DIDS,
nor a transepithelial bicarbonate gradient, altered propionate transport. A transepithelial pH gradient inhibited propionate
secretion, but not in a manner entirely consistent with the effect of pH on the distribution of a weak electrolyte. These
results suggest that there is significant segmental heterogeneity in colonic SCFA transport; that transepithelial propionate
fluxes are altered by changes in pH or electroneutral Na absorption (Na−H exchange), but not by chloride removal, bicarbonate
gradients or electrogenic Na absorption. Regulation of SCFA transport may be an important factor in the physiology of colonic
fluid balance. 相似文献
156.
157.
Abstract: The N-methyl-d -aspartate (NMDA) receptor possesses two distinct amino acid recognition sites, one for glutamate and one for glycine, which appear to be allosterically linked. Using rat cortex/hippocampus P2 membranes we have investigated the effect of glutamate recognition site ligands on [3H]glycine (agonist) and (±)4-trans-2-car-boxy-5,7-dichloro-4-[3H]phenylaminocarbonylamino-1,2,3,4-tetrahydroquinoline ([3H]l -689,560; antagonist) binding to the glycine site and the effect of glycine recognition site ligands on l -[3H]glutamate (agonist), dl -3-(2-carboxypiperazin-4-yl)-[3H]propyl-1 -phosphonate ([3H]-CPP; “C-7” antagonist), and cis-4-phosphonomethyl-2-[3H]piperidine carboxylate ([3H]CGS-19755; “C-5” antagonist) binding to the glutamate site. “C-7” glutamate site antagonists partially inhibited [3H]l -689,560 binding but had no effect on [3H]glycine binding, whereas “C-5” antagonists partially inhibited the binding of both radioligands. Glycine, d -serine, and d -cycloserine partially inhibited [3H]CGS-19755 binding but had little effect on l -[3H]-glutamate or [3H]CPP binding, whereas the partial agonists (+)-3-amino-1-hydroxypyrrolid-2-one [(+)-HA-966], 3R-(+)cis-4-methyl-HA-966 (l -687,414), and 1-amino-1-carboxycyclobutane all enhanced [3H]CPP binding but had no effect on [3H]CGS-19755 binding, and (+)-HA-966 and l -687,414 inhibited l -[3H]glutamate binding. The association and dissociation rates of [3H]l -689,560 binding were decreased by CPP and d -2-amino-5-phosphonopentanoic acid (“C-5”). Saturation analysis of [3H]l -689,560 binding carried out at equilibrium showed that CPP had little effect on the affinity or number of [3H]l -689,560 binding sites. These results indicate that complex interactions occur between the glutamate and glycine recognition sites on the NMDA receptor. In addition, mechanisms other than allosterism may underlie some effects, and the possibility of a steric interaction between CPP and [3H]l -689,560 is discussed. 相似文献
158.
Further Evidence for Multiple Forms of an N-Methyl-d-Aspartate Recognition Domain in Rat Brain Using Membrane Binding Techniques 总被引:1,自引:1,他引:0
Pingping Zuo Kiyokazu Ogita Takeo Suzuki Daiken Han Yukio Yoneda 《Journal of neurochemistry》1993,61(5):1865-1873
Abstract— Pretreatment with sulfhydryl-reactive agents, such as N-ethylmaleimide and p-chloromercuriphenylsul-fonic acid, invariably resulted in marked inhibition of the binding of dl -(E)-2-amino-4-[3H]propyl-5-phosphono-3-pentenoic acid ([3H]CGP 39653), a competitive antagonist at an N-methyl-d -aspartate (NMDA)-sensitive subclass of central excitatory amino acid receptors, in brain synaptic membranes extensively washed and treated with Triton X-100, but did not significantly affect the binding of L-[3H]-glutamic acid ([3H]Glu), an endogenous agonist. The pre-treatment was effective in reducing the binding of [3H]-CGP 39653 at equilibrium, without altering the initial association rate, and decreased the affinity for the ligand. Pretreatment with sulfhydryl-reactive agents also enhanced the potencies of NMDA agonists to displace [3H]-CGP 39653 binding and attenuated those of NMDA antagonists, but had little effect on the potencies of the agonists and antagonists to displace [3H]Glu binding. The binding of both [3H]CGP 39653 and [3H]Glu was similarly sensitive to pretreatment with four different proteases in Tritontreated membranes, whereas pretreatment with phospho-lipase A2 or C markedly inhibited [3H]CGP 39653 binding without altering [3H]Glu binding. Moreover, both phospho-lipases not only induced enhancement of the abilities of NMDA agonists to displace the binding of [3H]CGP 39653 and [3H]Glu, but also caused diminution of those of NMDA antagonists. These results suggest that both sulfhydryl-reactive agents and phospholipases may predominantly interfere with radiolabeling of the NMDA recognition domain in a state favorable to an antagonist by [3H]CGP 39653, with concomitant facilitation of that in an agonist-preferring form by [3H]Glu. The possible presence of multiple forms of the NMDA recognition domain is further supported by these data. 相似文献
159.
Abstract: Pretreatment with Triton X-100 more than doubled the binding of radiolabeled 5,7-dichlorokynurenic acid (DCKA), a proposed antagonist at a glycine (Gly) recognition domain on the N-methyl-d -aspartate (NMDA) receptor ionophore complex, in rat brain synaptic membranes. The binding exhibited an inverse temperature dependency, reversibility, and saturability, the binding sites consisting of a single component with a high affinity (27.5 nM) and a relatively low density (2.87 pmol/mg of protein). The binding of both [3H]DCKA and [3H]Gly was similarly displaced by numerous putative agonists and antagonists at the Gly domain in a concentration-dependent manner at a concentration range of 100 nM to 0.1 mM. Among the 24 putative ligands tested, DCKA was the second most potent displacer of the binding of both radioligands with no intrinsic affinity for the binding of [3H]kainic acid and α-amino-3-hydroxy-5-[3H]methylisoxazole-4-propionic acid (AMPA) to the non-NMDA receptors. In contrast, the other proposed potent Gly antagonist, 5,7-dinitroquinoxaline-2,3-dione, was active in displacing the binding of [3H]glutamic ([3H]Glu) and D,L-(E)-2-amino-4-[3H]propyl-5-phosphono-3-pentenoic acids to the NMDA recognition domain with a relatively high affinity for the non-NMDA receptors. In addition, the proposed antagonist at the AMPA-sensitive receptor, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline, not only displaced weakly the binding of both [3H]- Gly and [3H]DCKA, but also inhibited the binding of (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ([3H]MK-801) to an ion channel associated with the NMDA-sensitive receptor in the presence of added Glu alone in a manner sensitive to antagonism by further added Gly. Clear correlations were seen between potencies of the displacers to displace [3H]DCKA binding and [3H]Gly binding, in addition to between the potencies to displace [3H]-DCKA or [3H]Gly binding and to potentiate or inhibit [3H]MK-801 binding. All quinoxalines tested were invariably more potent displacers of [3H]DCKA binding than [3H]Gly binding, whereas kynurenines were similarly effective in displacing the binding of both [3H]Gly and [3H]-DCKA. These results undoubtedly give support to the proposal that [3H]DCKA is one useful radioligand available in terms of its high selectivity and affinity for the Gly domain in the brain. Possible multiplicity of the Gly domain is suggested by the differential pharmacological profiles between the binding of [3H]Gly and [3H]DCKA. 相似文献
160.
Taojun He Fang Zhang Jin Zhang Shanshan Wei Jie Ning Hanmei Yuan Bin Li 《Helicobacter》2023,28(3):e12959