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31.
Dr. Radivoj Krstić 《Cell and tissue research》1985,241(3):677-681
Summary Autophagosome formation in rat and gerbil pinealocytes is described. It starts with the setting up of a tubular acid phosphatase-rich cisterna which gradually wraps around cytoplasmic areas to be catabolized. In light of obtained findings, it seems that the autophagosome formation in pinealocytes is a type of lysosome wrapping mechanism. 相似文献
32.
Germination of freshly harvested seeds of a non-dormant (ND) line (Stonehouse 319) of wild oats ( Avena fatua L.) was inhibited by incubation of the seeds at relatively high temperatures of 25 and 30°C. The germination inhibition in these seeds appeared to be a case of thermo-inhibition which was the direct effect of hightemperature treatment (HIT), since it did not persist after transferring the seeds to an optimum germination temperature of 20°C. Even a prolonged HTT of 30°C for over 5 weeks did not prevent germination of about 80% of the seeds transferred to 20°C. However, in a significant proportion of the seeds, thermo-dormancy was induced by 10 days of HTT at 30°C if the seeds were then incubated at sub-optimal temperatures of 5 to 15°C. This thermo-dormancy would appear to be 'restrictive' in form, since its expression was restricted to very specific conditions. Relatively low inclubation temperaturs of 5 and 10°C markedly slowed germination whether HTT was applied or not. The results suggest that thermo-inhibition and thermo-dormancy, induced during seasonal temperature fluctuations, may provide a survival mechanism for seeds of such ND lines as Stonehouse 319. 相似文献
33.
The reactions of singlet oxygen (1O2) with cis and trans butenes-1,1,1-d3, at—80°C in Freon-11, show a product isotope effect (kH/kD) of 1.38 and 1.25 respectively. Isomerization of the starting materials or formation of dioxetanes were not observed during the course of the photooxygenation. Together with the isotope effects on the reactions of tetramethylethylene-d6 isomers with singlet oxygen, these results require the reversible formation of a perepoxide or charge transfer intermediate. 相似文献
34.
High light treatments were given to attached leaves of pumpkin (Cucurbita pepo L.) at room temperature and at 1°C where the diffusion- and enzyme-dependent repair processes of Photosystem II are at a minimum. After treatments, electron transfer activities and fluorescence induction were measured from thylakoids isolated from the treated leaves. When the photoinhibition treatment was given at 1°C, the Photosystem II electron transfer assays that were designed to require electron transfer to the plastoquinone pool showed greater inhibition than electron transfer from H2O to paraphenyl-benzoquinone, which measures all PS II centers. When the light treatment was given at room temperature, electron transfer from H2O to paraphenyl-benzoquinone was inhibited more than whole-chain electron transfer. Variable fluorescence measured in the presence of ferricyanide decreased only during room-temperature treatments. These results suggest that reaction centers of one pool of Photosystem II, non-QB-PS II, replace photoinhibited reaction centers at room temperature, while no replacement occurs at 1°C. A simulation of photoinhibition at 1°C supports this conclusion.Abbreviations BSA
bovine serum albumin
- Chl
chlorophyll
- DCMU
3-(3,4,-dichlorophenyl)-1,1,-dimethylurea
- DCPIP
dichlorophenol-indophenol (2,6-dichloro-4((4-hydroxyphenyl)imino)-2,5-cyclohexadien-1-one)
- DPC
diphenyl carbazide (2,2-diphenylcarbonic dihydrazide)
- FeCN
ferricyanide (hexacyanoferrate(III))
- app
apparent quantum yield of photosynthetic oxygen evolution
- MV
methyl viologen (1,1-dimethyl-4,4-bipyridinium dichloride)
- PPBQ
phenyl-p-benzoquinone
- PPFD
photosynthetic photon flux density
- PQ
pool plastoquinone
- QB
secondary quinone acceptor of PS II
- RT
room temperature
- WC
whole chain electron transfer 相似文献
35.
Luísa M. D. R. S. Martins Armando J. L. Pombeiro Richard A. Henderson 《Inorganica chimica acta》1996,250(1-2):311-315
The kinetics of the displacement reactions of the bromide ligands of trans-[FeBr2(depe)2] (depe = Et2PCH2CH2PEt2) by the organonitrile NCCH2C6H4OMe-4, in tetrahydrofuran (either in the absence or in the presence of added Br−), to give the corresponding mono- and dinitrile complexes trans-[FeBr(NCCH2C6H4OMe-4)(depe)2]+ and trans-[Fe(NCCH2C6H4OMe-4)2(depe)2]2+, have been investigated by stopped-flow spectrophotometry. The substitution reaction occurs by a mechanism involving rate-limiting dissociation of bromo ligands to form the unsaturated intermediates [FeBr(depe)2]+ (k1 = 1.52 ± 0.02 s−1) and [Fe(NCR)(depe)2]2+ (k3 = 0.063 ± 0.008 s−1) which add the nitrile ligand to form those nitrile complexes. The competition between the nitrile and Br− for such metal centres has also been investigated and a stronger inhibiting effect of added Br− is observed for the substitution of the second bromo ligand relative to the first one. The kinetic data are rationalized in terms of π-electronic effects of these unsaturated metal centres and of the bromide and nitrile ligands. 相似文献
36.
37.
38.
Substituted enzyme (or ping-pong) mechanisms usually involve enzymes that exist in two forms that alternate during the catalytic
reaction. A method is described here for determining the position of the equilibrium of a half reaction in a ping-pong enzyme
mechanism that is based on the kinetics of the burst reaction which occurs upon addition of reactants that recycle the enzyme
from one form to another. The theoretical basis for the analysis is developed, and the method is applied to the half reaction
of the aldimine form of aspartate transaminase with difluoro-oxaloacetate.
Special issue dedicated to Herman Bachelard 相似文献
39.
Gordon C. K. Roberts 《Neurochemical research》1996,21(9):1117-1124
NMR spectroscopy has proved to be a valuable tool in the study of the interactions between enzymes and their substrates. The
kinds of structural and dynamic information which can be obtained are illustrated by studies of three enzymes involved in
drug metabolism. Cytochromes P450 play a crucial role in metabolism of a wide range of exogenous chemicals. NMR has been used to measure distances from the
haem iron of the cytochrome to protons of the bound substrate, leading to detailed structural models for the enzyme-substrate
complexes. The other two enzymes, chloramphenicol acetyltransferase and β-lactamase, are responsible for bacterial resistance
to specific antibiotics. In chloramphenicol acetyltransferase, NMR has been used to determine the conformation of coenzyme
A bound to the enzyme, while in the case of β-lactamase the pK of a specific lysine residue at the active site has been determined,
providing valuable information on the catalytic mechanism.
Special issue dedicated to Dr. Herman Bachelard. 相似文献
40.
This study examined the localized action of neuropeptide Y (NPY) on monoamine transmitter activity in the hypothalamus of
the unrestrained rat as this peptide induced hypothermia, spontaneous feeding or both responses simultaneously. A guide tube
was implanted in the anterior hypothalamic pre-optic area (AH/POA) of Sprague-Dawley rats. Then either control CSF vehicle
or NPY in a dose of either 100 ng/μl or 250 ng/μl was perfused by push-pull cannulae in this structure in the fully sated,
normothermic rat. Successive perfusions were carried out at a rate of 20 μl/min for 6.0 min with an interval of 6.0 min elapsing
between each. Samples of perfusate were assayed by HPLC for their levels of dopamine (DA), norepinephrine (NE), serotonin
(5-HT) and their respective metabolites. Whereas control CSF was without effect on body temperature (Tb) or feeding, repeated perfusions of NPY over 3.0 hr caused dose—dependent eating from 4 to 39 g of food, hypothermia of 0.9
to 2.3°C or both responses concurrently. As the rats consumed 11–39 g of food, the efflux of NE, MHPG, DOPAC and 5-HT was
enhanced significantly, whereas during the fall in Tb the efflux of NE, DOPAC and 5-HIAA from the AH/POA increased. When the Tb of the rat declined simultaneously with eating behavior, the levels in perfusate of DOPAC and HVA increased significantly
while MHPG declined. During perfusion of the AH/POA with NPY the turnover of NE declined while DA and 5-HT turnover increased
during hypothermia alone or when accompanied by feeding. These results demonstrate that the sustained elevation in NPY within
the AH/POA causes a selective alteration in the activity of the neurotransmitters implicated in thermoregulation, satiety
and hunger. These findings suggest that both DA and NE comprise intermediary factors facilitating the action of NPY on neurons
involved in thermoregulatory and ingestive processes. The local activity of NPY on hypothalamic neurons apparently shifts
the functional balance of serotonergic and catecholaminergic neurons now thought to play a primary role in the control of
energy metabolism and caloric intake. 相似文献