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61.
Detection of rapid induction kinetics with a new type of high-frequency modulated chlorophyll fluorometer 总被引:21,自引:0,他引:21
U. Schreiber 《Photosynthesis research》1986,9(1-2):261-272
A newly developed modulation fluorometer is described which operates with 1 sec light pulses from a light-emitting diode (LED) at 100 KHz. Special amplification circuits assure a highly selective recording of pulse fluorescence signals against a vast background of non-modulated light. The system tolerates ratios of up to 1:107 between measuring light and actinic light. Thus it is possible to measure the dark fluorescence yield and record the kinetics of light-induced changes. A high time resolution allows the recording of the rapid relaxation kinetic following a saturating single turnover flash. Examples of system performance are given. It is shown that following a flash the reoxidation kinetics of photosystem II acceptors are slowed down not only by the inhibitor DCMU, but by a number of other treatments as well. From a light intensity dependency of the induction kinetics the existence of two saturated intermediate levels (I1 and I2) is apparent, which indicates the removal of three distinct types of fluorescence quenching in the overall fluorescence rise from F0 to Fmax.Abbreviations QA and QB
consecutive electron acceptors of photosystem II
- PS II
photosystem II
- P 680
reaction center chlorophyll of photosystem II
- F0
minimum fluorescence yield following dark adaptation
- Fmax
maximum fluorescence yield
- DCMU
3-(3, 4-dichlorophenyl)-1, 1-dimethyl-urea
- DCCD
N,N-dicyclohexylcarbodiimide
- PQ
plastoquinone
- DAD
diaminodurene
Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement. 相似文献
62.
J. L. Smith M. M. Bencivengo R. L. Buchanan C. A. Kunsch 《Archives of microbiology》1986,144(2):131-136
In this study, we investigated the relationship between carbohydrate metabolism and repression of staphylococcus enterotoxin A (SEA) in Staphylococcus aureus 196E and a pleiotrophic mutant derived from strain 196E. The mutant, designated at strain 196E-MA, lacked a functional phosphoenolpyruvate phosphotransferase system (PTS). The mutant produced acid, under aerobic conditions, from only glucose and glycerol. The parent strain contained an active PTS, and aerobically produced acid from a large number of carbohydrates. Prior growth in glucose led to repression of SEA synthesis in the parent strain; addition to the casamino acids enterotoxin production medium (CAS) led to more severe repression of toxin synthesis. The repression was not related to pH decreases produced by glucose metabolism. When S. aureus 196E was grown in the absence of glucose, there was inhibition of toxin production as glucose level was increased in CAS. The inhibition was related to pH decrease and was unlike the repression observed with glucose-grown strain 196E. The inhibition of SEA synthesis in mutant strain 196E-MA was approximately the same in cells grown with or without glucose and was pH related. Repression of SEA synthesis similar to that seen with glucose-grown S. aureus 196E could not be demonstrated in the mutant. In addition, glucose-grown S. aureus 196E neither synthesized -galactosidase nor showed respiratory activity with certain tricarboxylic acid (TCA) cycle compounds. Glucose-grown strain 196E-MA, however, did not show supressed respiration of TCA cycle compounds; -galactosidase was not synthesized because the mutant lacked a functional PTS. Cyclic adenosine-3, 5-monophosphate did not reverse the repression by glucose of SEA or -galactosidase synthesis in glucose-grown S. aureus 196E. An active PTS appears to be necessary to demonstrate glucose (catabolite) repression in S. aureus.Abbreviations SEA
staphylococcal enterotoxin A
- SEB
staphylococcal enterotoxin B
- SEC
staphylococcal enterotoxin C
- PTS
phosphoenolpyruvate phosphotransferase system
- CAS
casamino acids salts medium
- TCA
tricarboxylic acid cycle 相似文献
63.
Summary Mutations in seven different maternal-effect loci on the second chromosome of Drosophila melanogaster all cause alterations in the anterior-posterior pattern of the embryo. Mutations in torso (tor) and trunk (trk) delete the anterior- and posterior-most structures of the embryo. At the same time they shift cellular fates which are normally found in the subterminal regions of the embryo towards the poles. Mutations in vasa (vas), valois (vls), staufen (stau) and tudor (tud) cause two embryonic defects. For one they result in absence of polar plasm, polar granules and pole cells in all eggs produced by mutant females. Secondly, embryos developing inside such eggs show deletions of abdominal segments. In addition, embryos derived from staufen mothers lack anterior head structures, embryos derived from valois mothers frequently fail to cellularize properly. Mutations in exuperantia (exu) cause deletions of anterior head structures, similar to torso, trunk and staufen. However in exu, these head structures are replaced by an inverted posterior end which comprises posterior midgut, proctodeal region, and often malpighian tubules.The effects of all mutations can be traced back to the beginning stages of gastrulation, indicating that the alterations in cellular fates have probably taken place by that time. Analysis of embryos derived from double mutant mothers suggests that these three phenotypic groups of mutants interfere with three different, independent pathways. All three pathways seem to act additively on the system which specifies anterior-posterior cellular fates within the egg. 相似文献
64.
Ole G. Mouritsen 《生物化学与生物物理学报:生物膜》1983,731(2):217-221
The gel-to-fluid first-order melting transition of lipid bilayers is simulated by the use of a microscopic interaction model which includes a variable number of lipid-chain conformational states. The results suggest that the experimental observation of ‘continuous melting’ in pure wet lipid bilayers, rather than being ascribed to the presence of impurities, may be explained as a result of kinetically caused metastability of intermediate lipid-chain conformations. 相似文献
65.
Casein kinase-TS (Ck-TS), a type-2 casein kinase purified from rat liver cytosol which phosphorylates seryl and threonyl residues N-terminal to acidic clusters, is specifically inhibited by polyglutamyl peptides which are ineffective both on type-1 casein kinase and on cAMP-dependent protein kinase. The inhibition is competitive toward the protein substrate and non-competitive toward ATP. Among the polyglutamates tested (Glu)70 is the most effective (Ki 0.11 microM). (Glu)10 and (Glu)5 are also inhibitors, though less powerful than (Glu)70, while (Glu)3, (Glu)2 and free glutamic acid up to 5 mM are ineffective. These results disclose the possibility that naturally occurring polypeptides containing long stretches of acidic residues may act as physiological inhibitors of type-2 casein kinases. 相似文献
66.
Adult sockeye salmon, Oncorhynchus nerka (Walbaum), treated with salmon pituitary extract in July survived for up to 47 days and developed nuptial colours in both male and female fish during this period, whereas no such characteristics appeared in untreated control fish. Furthermore, results showed that 20 of 50 adult female Philomena oncorhynchi recovered from the 15 treated fish contained fully developed tailed larvae in the uterus as compared with only one of 44 female P. oncorhynchi from 31 untreated control fish. None of 51 worms from 13 stilboestrol treated adult sockeye showed development in utero beyond an elongated embryo, nor did the host fish develop nuptial colours. P. oncorhynchi and its immature sockeye host (approx. 1 year prior to spawning) remained unaffected by any of three separate hormone treatment experiments using injection of salmon pituitary extract, injection of 17-β-estradiol, and stilboestrol mixed in the food. 相似文献
67.
We treat the transport of univalent cations through pore-like protein channels in biological membranes analytically, using two models (A + B) for the channel and the ion-channel interaction. A Lennard-Jones-type repulsion between the ions and the pore wall is introduced. We also include Van der Waals- and coulomb-type interactions between polar ligands of the pore-forming protein (e.g., carbonyl groups directed towards the axis of the channel) and the migrating particles. In model A, the polar groups are assumed to occur in pairs of dipoles pointing in opposite directions (as in the gramicidin A channel), while in model B the channel is treated as a pore with a radially isotropic charge distribution. In both models the ion-channel interaction leads to the occurrence of periodic potentials, corresponding to quasi-equilibrium and transition state sites of the ion in the pore. The diffusion rate can be calculated employing rate-theoretical concepts on the basis of microscopic parameters. It is demonstrated that the anomaly (inversion of the normal mass effect) for the transport rates of different ions can be related to differences in the activation entropy. The latter quantity is estimated analytically for both models. As a test, we performed numerical calculations with parameters based on the gramicidin A model. The results are in good agreement with experimental data and data from computer simulations. This shows that simple analytic expressions are well suited for predicting trends in the ionic conductivity of protein channels on the basis of microscopic interactions. 相似文献
68.
“生态效益”的内涵及其特征 总被引:1,自引:0,他引:1
纵观全球,伴随着社会、经济的迅速发展,环境问题已成为一个日趋突出的世界性问题,并对人民生命健康和社会、经济的持续稳定发展带来了严重威胁。生态学界强烈地呼吁人类要保护自然,维持生态平衡,合理地开发利用自然资源,呼吁人类在经济发展中能正确处理经济发展-环境保护,经济效益-生态效益的关系,在实践中取得了一定成效。然而,迄今为止我们对“生态效益”的内涵及特征还没有完全认识和了解,这在相当程度上妨碍了人们在社会生产中对提高生态效益的关注,因此,本问题亟待在理论上加以认识。本文试图对此做一点有益的探讨。 相似文献
69.
The contribution of drug metabolites to cyproheptadine (CPH)-induced alterations in endocrine pancreatic -cells was investigated by examining the inhibitory activity of CPH and its biotransformation products, desmethylcyproheptadine (DMCPH), CPH-epoxide and DMCPH-epoxide, on hormone biosynthesis and secretion in pancreatic islets isolated from 50-day-old rats. Measurement of (pro)insulin (proinsulin and insulin) synthesis using incorporation of 3H-leucine showed that DMCPH-epoxide, DMCPH and CPH-epoxide were 22, 10 and 4 times, respectively, more potent than CPH in inhibiting hormone synthesis. The biosynthesis of (pro)insulin was also inhibited by CPH and DMCPH-epoxide in islets isolated from 21-day-old rat fetuses. The inhibitory action of CPH and its metabolites was apparently specific for (pro)insulin, and the synthesis of other islet proteins was not affected. Other experiments showed the metabolites of CPH were active in inhibiting glucose-stimulated insulin secretion but were less potent than the parent drug in producing this effect. CPH and its structurally related metabolites, therefore, have differential inhibitory activities on insulin synthesis and release. The observation that CPH metabolites have higher potency than CPH to inhibit (pro)insulin synthesis, when considered with published reports on the disposition of the drug in rats, indicate that CPH metabolites, particularly DMCPH-epoxide, are primarily responsible for the insulin depletion observed when the parent compound is given to fetal and adult animals.Abbreviations CPH
cyproheptadine
- CPH-epoxide
cyproheptadine-10-11-epoxide
- DMCPH
desmethylcyproheptadine
- DMCPH-epoxide
desmethylcyproheptadine-10,11-epoxide
- HPLC
high-performance liquid chromatography
- KBB
Krebs biocarbonate buffer
Recipient of a Society of Toxicology Predoctoral Research Fellowship.Present address: Department of Biochemistry, The University of Hong Kong, Hong Kong. 相似文献
70.
A significant circadian rhythm of acute toxicity was demonstrated in mice with intraperitoneal (i.p.) injection of sodium valproate (VPA). The role of pharmacokinetics on the rhythms of the toxicity and electroshock seizure (ES) threshold was investigated. ICR male mice, housed under a light-dark (12 :12) cycle, were injected intraperitoneally 1200 mg/kg for the acute toxicity study and 300 mg/kg for the anticonvulsant effect study. In the acute toxicity, the highest mortality was found when VPA was injected at 1700 and the lowest at 0900 or 0100. The time course of mean plasma and brain VPA concentrations after an injection of VPA was not different between mice injected at 1700 and mice injected at 0100. In the anticonvulsant effect, no significant circadian rhythm was demonstrated for both the ES threshold and the plasma VPA concentrations after i.p. Injection, although a significant rhythm has been reported for them after oral administration. The results suggest that the circadian rhythm in the mortality after an i.p. Injection of VPA may be due to the rhythm in the sensitivity of the central nervous system to the drug and that the mechanism underlying the rhythm of VPA acute toxicity is different from that of the anticonvulsant action of VPA. The route and the time of drug administration are essentially important to study the anticonvulsant effect and acute toxicity of VPA in mice. 相似文献