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81.
Selenium is known to play an important role in the physiology of many different cell types and extracellular application of
selenite causes cellular dysfunction in many different types of tissues. In a previous study, we have shown that in rat ventricles,
sodium selenite (≥1 mM) caused an increase in the resting tension and a decrease in contractile force, in a time-dependent manner. In the present
study, we have shown that sodium selenite caused a contracture state both in Langendorff perfused hearts and isolated papillary
muscles. We also showed that the application of extracellular ATP (0.1 mM) markedly reduced this detrimental effect of sodium selenite on ventricular contraction in Langendorff perfused hearts and
delayed it in isolated papillary muscle preparations. In contrast, isoproterenol (0.1 μM) did not seem to influence this action of sodium selenite in papillary muscle preparations. Possible reasons for this protective
effect of ATP to selenite-induced contracture are also discussed. 相似文献
82.
Berry S 《Journal of molecular evolution》2002,54(5):595-613
All organisms rely on chemiosmotic membrane systems for energy transduction; the great variety of participating proteins
and pathways can be reduced to a few universal principles of operation. This chemical basis of bioenergetics is reviewed with
respect to the origin and early evolution of life. For several of the cofactors which play important roles in bioenergetic
reactions, plausible prebiotic sources have been proposed, and it seems likely that these cofactors were present before elaborate
protein structures. In particular, the hydrophobic quinones require only a membrane-enclosed compartment to yield a minimum
chemiosmotic system, since they can couple electron transport and proton translocation in a simple way. It is argued that
the central features of modern bioenergetics, such as the coupling of redox reactions and ion translocation at the cytoplasmic
membrane, probably are ancient features which arose early during the process of biogenesis. The notion of a thermophile root
of the universal phylogenetic tree has been discussed controversially, nevertheless, thermophiles are interesting model organisms
for reconstructing the origin of chemiosmotic systems, since they are often acidophiles and anaerobic respirers exploiting
iron–sulfur chemistry. This perspective can help to explain the prominent role of iron–sulfur proteins in extant biochemistry
as well as the origin of both respiration and proton extrusion within the context of a possible origin of life in the vicinity
of hot vents.
Received: 6 June 2001 / Accepted: 16 October 2001 相似文献
83.
Streptococcus pyogenes grown in the presence of subinhibitory concentrations of sodium fluoride had a diminished ability, compared to control cells, to adhere to buccal cells, collagen, fibronectin, and laminin. In addition, sodium fluoride was a competitive inhibitor of streptococcal adhesion to collagen and fibronectin, but not laminin. It is suggested that sodium fluoride may be useful in therapy or prophylaxis in infections involving group A streptococci. 相似文献
84.
85.
Sodium propionate, as well as sodium butyrate, enhanced the production of recombinant B-domain-deleted, factor VIII (rFVIIIdB) by Chinese hamster ovary cells growing in a spinner-flask with a protein-free medium by more than six-fold. The two acids, however, had different cytotoxicities. 相似文献
86.
Evidence of cytochrome P450-catalyzed cleavage of the ether bond of phenoxybutyrate herbicides in Rhodococcus erythropolis K2-3 总被引:3,自引:0,他引:3
Bacterial strain Rhodococcus erythropolis K2-3 can cleave theether bond of the phenoxybutyrate herbicides, i.e., 4-(2,4-dichlorophenoxy)butyrate(2,4-DB) and 4-(4-chloro-2-methylphenoxy)butyrate (MCPB), by anenzyme system that is constitutively expressed. The enzyme(s) involved were investigated in this study. The rate ofdisappearance of 2,4-DB determined in a whole cell assay amounted to0.6 mmol/h ¶ gdry mass.Carbon monoxide difference spectra of dithionite-reduced wholecells and crude cell extracts suggested that strain K2-3 contains a soluble cytochrome P450(P450), named P450PB-1. The addition of various phenoxybutyrate substrates to crude cell extracts resulted in typical difference spectra following the type I pattern ofsubstrate binding with P450. The rate of 2,4-DB cleavage was reduced by inhibitors of P450: 5 mM metyrapone and carbon monoxide at a CO/O2 ratio of 10 reduced the activity by about 20%, and 70%, respectively. The ether cleaving activity completely disappearedafter disruption of the cells and could not be detected in crude extracts. To elucidate theenzymatic basis of this reaction, P450 was partially purified. With the resulting enzyme preparation,2,4-DB cleavage activity was re-established, becoming measurable after the addition of eitherphenazine methosulfate or ferredoxin and ferredoxin/NADP oxidoreductase from spinach. We detected no activities attributable to -ketoglutarate-dependent dioxygenase orNAD(P)H-dependent monooxygenase. These results collectively indicatethat cleavage of the ether bond of phenoxybutyrate herbicides is catalyzed by P450-mediated activityin this strain. One of the products derived from this reaction is dichlorophenol, and comparativechromatographic analyses suggest that the other product is a C4-carbonicacid, most likely succinic semialdehyde/succinate. 相似文献
87.
Takeda Y 《The Journal of steroid biochemistry and molecular biology》2003,85(2-5):443-447
Mineralocorticoid receptor (MR) binding is tightly regulated by the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSDII) which selectively metabolizes glucocorticoids to inactive metabolites, thus allowing for MR activation by aldosterone. To examine whether this enzyme is involved in the pathophysiology of salt-sensitive hypertension, 11β-HSDII activity and messenger RNA (mRNA) levels were determined in blood vessels of Dahl Iwai salt-sensitive (DS) and salt-resistant (DR) rats. Decreased 11β-HSDII activity and mRNA levels in mesenteric arteries were observed in 8-week-old DS rats on a high-salt diet, indicating that 11β-HSDII may play a significant role in salt sensitivity and hypertension. It has been suggested that mineralocorticoids act on blood vessels, leading to increased vasoreactivity and peripheral resistance. We present direct evidence that blood vessels are aldosteronogenic. The production of aldosterone in blood vessels was compared between stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. Vascular aldosterone and CYP11B2 mRNA levels were significantly increased in 2-week-old SHRSP versus WKY rats. However, the vascular aldosterone levels in 4- and 9-week-old SHRSP and WKY rats were similar. High sodium intake further increased both blood pressure and vascular aldosterone synthesis in the SHRSPs. Both the local renin–angiotensin–aldosterone system (RAAS) and the vascular 11β-HSDII level are critically important in the pathophysiology of cardiovascular disorders. 相似文献
88.
The general purpose of this theoretical work is to contribute to understand the physiological role of the electrogenic properties
of the sodium pump, by studying a dynamic model that integrates diverse processes of ionic and water transport across the
plasma membrane. For this purpose, we employ a mathematical model that describes the rate of change of the intracellular concentrations
of Na+, K+ and Cl−, of the cell volume, and of the plasma membrane potential (V
m
). We consider the case of a nonexcitable, nonpolarized cell expressing the sodium pump; Na+, K+, Cl− and water channels, and cotransporters of KCl and NaCl in its plasma membrane. We particularly analyze here the conditions
under which the physiological V
m
can be generated in a predominantly electrogenic fashion, as a result of the activity of the sodium pump. A major conclusion
of this study is that, for the cell model considered, a low potassium permeability is not a sufficient condition for a predominantly
electrogenic generation of the V
m
by the sodium pump. The presence of an electroneutral exchange of Na+ and K+ represents a necessary additional requirement.
Received: 8 September 1999/Revised: 21 March 2000 相似文献
89.
Phase I trial of interleukin-2 and high-dose arginine butyrate in metastatic colorectal cancer 总被引:4,自引:0,他引:4
Douillard JY Bennouna J Vavasseur F Deporte-Fety R Thomare P Giacalone F Meflah K 《Cancer immunology, immunotherapy : CII》2000,49(1):56-61
Interleukin-2 (IL-2) and sodium butyrate allow rats to be cured of peritoneal carcinomatosis from colon cancer. We performed
a phase I trial of IL-2 and high-dose arginine butyrate (ArgB) in patients with advanced metastatic colorectal cancer. Patients and methods: From April to July 1997, six patients were included in the trail; they had a median age of 52 years, four had a performance
status of 0, two had a performance status of 1 with normal biological functions. All patients had received at least two prior
lines of chemotherapy. A fixed dose of 18 MIU/m2 IL-2,was administered by subcutaneous injection and ArgB was delivered via continuous intravenous infusion on days 1–6 with
escalating doses starting at 2 g kg−1 day−1. Results: The planned dose escalation was not possible because of toxicities. A daily ArgB dose of 2 g/kg was delivered for nine cycles.
Level 2 (4 g/kg) could not be delivered in three of the six patients because of liver toxicity. The dose-limiting toxicities
were fatigue and liver function disturbances. The maximum tolerated dose for ArgB was 3 g kg−1 day−1, in combination with IL-2 at 12 MIU m2 day−1. No clinical response was seen. Pharmacokinetic analysis showed large intra- and interindividual variations. Conclusion: This schedule with a high dose of ArgB proved to be highly toxic with liver insufficiency. We will be running another trial
with lower doses of ArgB calculated from the schedule used in the experimental model, starting at a dose of 20 mg kg−1 day−1 for ArgB and 200 000 UI kg−1 day−1 IL-2, every 8 h.
Received: 13 May 1999 / Accepted: 28 October 1999 相似文献
90.
The outer membrane complex of Chlamydia is involved in the initial adherence and ingestion of Chlamydia by the host cell. In order to identify novel proteins in the outer membrane of Chlamydia trachomatis L2, proteins were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. By silver staining of the protein profile, a major protein doublet of 100-110 kDa was detected. In-gel tryptic digestion and matrix-assisted laser desorption/ionization mass spectrometry identified these proteins as the putative outer membrane proteins PmpG and PmpH. 相似文献