Mercapturic acid formation, an established pathway in the detoxication of xenobiotics, is demonstrated for cysteinyl leukotrienes generated in rats
after endotoxin treatment. The mercapturate N-acetyl-leukotriene E4 (N-acetyl-LTE4) represented a major metabolite eliminated into bile after injection of [3H]LTC4 as shown by cochromatography with synthetic N-acetyl-LTE4 in four different HPLC solvent systems. The identity of endogenoud N-acetyl-LTE4 elicited by endotoxin
was additionally verified by enzymatic deacetylation followed by chemical N-acetylation. The deacetylation was catalyzed by penicillin amidase. Endogenous cysteinyl leukotrienes were quantified by radioimmunoassay after HPLC separation. A N-acetyl-LTE4 concentration of 80 nmol/l was determined in bile collected between 30 and 60 min after endotoxin injection. Under this condition, other cysteinyl leukotrienes detected in bile by radioimmunoassay amounted to less than 5% of N-acetyl-LTE4. The mercapturic acid pathway, leading from the glutathione conjugate LTC4 to N-acetyl-LTE4, thus plays an important role in the deactivation and elimination of these potent endogenous mediators. 相似文献
Using HeLa S-3 cells synchronized by selective detachment, in this paper we report a parallel study of nuclear morphology
and autoradiography grain patterns between middle G1 and middle S phases: Our results show two distinct [3H]-thymidine labeling patterns. The first “peripheral” labeling pattern has a characteristic nuclear size distribution, in
contrast to the heterogeneous and varying size distributions of Feulgen-stained nuclei, and apparently is characteristic of
very early S phase. The sizes of the second labeling pattern—homogeneous or inhomogeneous grain distribution throughout the
nucleus—are equal or larger than the first and vary with S phase progression. Together, the corresponding nuclear sizes of
the labeled nuclei represent the larger extreme of nuclear areas, and the labeling index closely parallels the fraction of
nuclei with areas larger than the minimum size of the labeled nuclei. These results suggest a characteristic nuclear size
(reflecting unique intranuclear DNA distribution) as a necessary, if not sufficient, requirement for S phase initiation. Parallel
experimentation with rat liver cells—synchronized in vivo by partial hepatectomy and analyzed by thin section autoradiography—confirms
the existence of a peripheral labeling pattern in both the very early part and the very late part of S phase, which reconciles
our data with previous results and points to the fact that both initiation and termination sites for DNA replication are near
the nuclear periphery. 相似文献
Summary The permeability and partition coefficients of tetraphenylarsonium (TPA) and several other organic cations were studied in the human erythrocyte using an ion-selective electrode. The permeability constant for the different cations could be explained quite well by differences in oil/water partition coefficients. No evidence for facilitated transport could be found. Binding of the organic ions occurred to both the cell membrane and to intracellular contents. Partitioning to the membrane remained relatively constant despite variation from ion intracellular binding with blood samples from different donors. TPA flux is stimulated by substoichiometric amounts of tetraphenylboron and other organic anions, suggesting an ion-pairing mechanism. 相似文献
In the isolated and perfused rat heart, the addition of morphine, methionine-enkephalin or leucine-enkephalin to the coronary perfusate, significantly reduces the mechanical activity by negatively affecting both the heart rate and the developed tension. These effects are dose dependent and maximally evident with leucine-enkephalin. Furthermore all the opioids strongly reduce the activity of isoproterenol-stimulated hearts. The suggestion is made that opioid peptides directly influence the cardiac mechanical activity possibly by interacting with membrane-receptor systems. 相似文献
An experimental system consisting of a gas exchange column linked to an assimilation chamber has been developed to record continuously the free dissolved CO2 concentration in seawater containing marine plants. From experiments performed on the red macroalga Chondrus crispus (Rhodophyta, Gigartinales), this measurement is in agreement with the free CO2 concentration calculated from the resistance to CO2 exchanges in a biphasic system (gas and liquid) as earlier reported. The response time of this apparatus is short enough to detect, in conditions of constant pH, a photosynthesis-caused gradient between free CO2 and HCO3− pools which half-equilibrates in 25 seconds. Abolished by carbonic anhydrase, the magnitude of this gradient increases with decreasing time of seawater transit from the chamber to the column apparatus. But its maximum magnitude (0.35 micromolar CO2) is negligible compared to the difference between air and free CO2 (11.4 micromolar CO2). This illustrates the extent of the physical limiting-step occurring at the air-water interface when inorganic carbon consumption in seawater is balanced by dissolving gaseous CO2. The direction of this small free CO2/HCO3− gradient indicates that HCO3− is consumed during photosynthesis. 相似文献
Previous studies from this laboratory have shown that the thermolysin fragment 121–316, comprising entirely the“all-α” COOH-terminal
structural domain 158–316, as well as fragment 206–316 (fragment FII) are able to refold into a native-like, stable structure
independently from the rest of the protein molecule. The present report describes conformational properties of fragments 228–316
and 255–316 obtained by chemical and enzymatic cleavage of fragment FII, respectively. These subfragments are able to acquire
a stable conformation of native-like characteristics, as judged by quantitative analysis of secondary structure from far-ultra-violet
circular dichroism spectra and immunochemical properties using rabbit anti-thermolysin antibodies. Melting curves of the secondary
structure of the fragments show cooperativity with a temperature of half-denaturationTmof 65–66°C. The results of this study provide evidence that it is possible to isolate stable supersecondary structures (folding
units) of globular proteins and correlate well with predictions of subdomains of the COOH-terminal structural domain 158–316
of thermolysin. 相似文献
Some a priori and a posteriori aspects of the identifiability problem for unidentifiable models are discussed. It is argued that the nation of identifiability from parameter bounds has a minor a priori structural relevance. The parameter bounds rationale may prove a useful a posteriori numerical notion. However, its practical potentiality needs careful evaluation, as the use of point estimates automatically builds into the model some hidden structural constraints. Examples are given. 相似文献
Activity levels of 7-ethoxycoumarin O-deethylase (ED), aminopyrine N-demethylase (APD), p-nitroanisoleO-demethylase (p-NAD) and glucose-6-phosphate dehydrogenase (G-6-PDH) were determined in incubation mixtures for the liver-microsomal assay (LMA) at time 0 and after 1 and 2 h incubation under conditions for mutagenic assay. The experiments were performed with S9 liver fractions from mice (induced with Na-phenobarbital and β-naphthoflavone) and rats (induced with Aroclor 1254) with and without G-6-PDH in the incubation mixtures.
In the absence of G-6-PDH the activities were significantly lower at time 0 in the mouse. The pattern of stability, however, was similar for the activities, with an increase of stability after 1 and 2 h of pre-incubation (an exception for p-NAD).
Only ED activity showed a similar behaviour in the rat. No differences were present for APD and p-NAD activities at time 0 in the rat, but the enzyme stabilities were significantly decreased after 2 h of incubation (about 15% and 10% for APD and p-NAD respectively) in the absence of G-6-PDH.
At time 0, the amounts of G-6-PDH differed between mouse and rat fractions; however, during the incubations for LMA they decreased by about 57% and 53% for the two species, respectively. In addition to the above biochemical results, the presence of exogenous G-6-PDH in the incubations for the mutagenic assay, significantly increased the mitotic gene conversion and mitotic crossing-over of dimethylnitrosamine (DMN) and AR2MNFN (a nitroimidazo[2,1-b]thiazole) in the D7 strain of Saccharomyces cerevisiae. 相似文献
We have compared the effects of estradiol on the [3H]thymidine (TdR) incorporation into the DNA of 2 rat tissues whose growth is controlled by estradiol in vivo in 2 opposite directions: the normal anterior pituitary and the MtF4 pituitary tumor transplanted under the kidney capsule. Small pieces of pituitary or tumor from Fischer rats, treated or not by estradiol in silastic tubing, were incubated in vitro with [3H]TdR. The [3H]TdR incorporated per microgram DNA was decreased in tumor after 2 to 8 day-estradiol treatment while simultaneously, in the same rats, it was increased in the pituitary. In addition, we studied the effect of estradiol in vitro on the F4C1 cell line obtained from the MtF4 tumor. A dose-dependent decrease of both the [3H]TdR incorporated into DNA and the DNA amount was observed between 10(-6) and 10(-5) M estradiol. These results suggest that the control of the pituitary or MtF4 tumor growth by estradiol in vivo is in part due to an inhibition of cell multiplication. Although estradiol inhibits the growth of a clone of MtF4 tumor cells in vitro we cannot decide whether or not the in vivo effect of estradiol is direct. 相似文献