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81.
When detergent-derived photosystem II (PSII) membranes are treated with CaCl2 to remove the three extrinsic proteins associated with the O2-evolving complex, the resulting membranes (CaPSII) can still catalyze water oxidation if sufficient Ca2+ and Cl- are present. When CaPSII membranes are exposed to single turnover flashes on an O2 rate electrode, anomalous O2 is produced by the first two flashes. The addition of catalase to the membrane suspension completely inhibits O2 produced by the first two flashes, but not by subsequent flashes. Exogenous H2O2 stimulates anomalous O2 production by the first few flashes in CaPSII membranes, but not in control PSII membranes. Diuron (DCMU) does not inhibit H2O2-stimulated O2 production by the first flash. However, it does inhibit the O2 yield of all subsequent flashes, indicating that all flash-induced O2 signals in CaPSII membranes are dependent on photosystem II electron transport. H2O2 stimulation of O2 yields is inhibited in Tris-, heat-, and EDTA-(ethylenediaminetetraacetic acid)-treated CaPSII. In the presence of high salt, H2O2 (but not EDTA) treatment of CaPSII, extracts Mn functional in normal photosynthetic O2 evolution. The addition of exogenous Mn2+ reconstitutes anomalous O2 production in Tris-and H2O2/EDTA-treated CaPSII preparations but only in the presence of H2O2. Anomalous H2O2-stimulated O2 production can be observed both with a Clark electrode (steady state) and an O2 rate electrode (flash sequence). The mechanism involves electron donation from H2O2, mediated by free Mn2+, to PSII, and the 33-kDa extrinsic protein under some conditions can block this process. Since H2O2 can remove functional Mn from CaPSII membranes, its presence can convert functional Mn to the Mn2+ mediator state required for anomalous O2 production. EDTA binds Mn in CaPSII disrupted by H2O2 and prevents anomalous O2 evolution.Abbreviations CaPSII
a PSII preparation washed with approximately 1M CaCl2
- Chl
chlorophyll
- DCBQ
2,6-dichloro-p-benzoquinone
- DCMU (diuron)
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- EDTA
ethylenediaminetetraacetic acid
- MES
2-[N-morpholino]-ethanesulfonic acid
- PSII
a detergent-derived photosystem II membrane preparation
- RC
reaction center
- Tris
tris(hydroxymethyl)-aminomethane
- Yn
oxygen rate electrode flash yield resulting from the nth flash of a sequence of single turnover flashes of light
Operated by the Midwest Research Institute for the U.S. Department of Energy under contract DE-AC02-83CH10093. 相似文献
82.
盾叶薯蓣地上部分的三个新甾体皂甙 总被引:11,自引:0,他引:11
从盾叶薯蓣Dioscorea zingiberensis Wright地上部分分离鉴定了四个甾体皂甙,经鉴定甙A为约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)]-β-D-葡萄吡喃糖甙;甙B为24α-羟基约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)]β-D-葡萄吡喃糖甙;甙C为约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)][β-D-葡萄吡喃糖基(1→4)]-β-D-葡萄吡喃糖基;甙D为约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)][β-D-葡萄吡喃糖基(1→3)]-β-D-葡萄吡喃糖甙。前三者为新化合物,分别命名为盾叶皂甙A_1、A_2、A_3(zingiberoside A_1、A_2、A_3),其中盾叶皂甙A_2的甙元为一新甾体皂甙元,命名为盾叶皂甙元(zingiberogenin)。 相似文献
83.
Enzymic Synthesis of Leukotriene B4 in Guinea Pig Brain 总被引:9,自引:8,他引:1
Takao Shimizu Yutaka Takusagawa Takashi Izumi Nobuya Ohishi Yousuke Seyama 《Journal of neurochemistry》1987,48(5):1541-1546
Leukotriene B4 [5(S), 12(R)-dihydroxy-6, 14-cis-8,10-trans-eicosatetraenoic acid] was obtained from endogenous arachidonic acid when slices of the guinea pig brain cortex were incubated with the calcium ionophore A 23187. Enzymes involved in its synthesis, arachidonate 5-lipoxygenase [arachidonic acid to 5(S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid and subsequently to leukotriene A4] and leukotriene A4 hydrolase (leukotriene A4 to B4), were present in the cytosol fraction. Arachidonate 5-lipoxygenase was Ca2+-dependent, and was stimulated by ATP and the microsomal membrane, as was noted for the enzyme from mast cells. The lipid hydroperoxides stimulated 5-lipoxygenase by four- to sixfold. The leukotriene A4 hydrolase activity was rich in brain, and the specific activity (0.4 nmol/min/mg of protein) was much the same as that of guinea pig leukocytes. High activities of these enzymes were detected in the olfactory bulb, pituitary gland, hypothalamus, and cerebral cortex. Since leukotriene B4 is enzymically synthesized in the brain, possible roles related to neuronal functions or dysfunctions deserve to be examined. 相似文献
84.
Effect of Digestion with Phospholipase A2 on Endogenous Protein Phosphorylation in Particulate Fractions from Rat Brain Synaptosomes 总被引:1,自引:1,他引:0
The endogenous phosphorylation of synapsin 1 in cyclic AMP-containing media was greatly decreased by digestion of synaptic vesicles and synaptosomal membranes with phospholipase A2, suggesting that the system is functionally dependent on the membrane structure. Treatment of the synaptic vesicle fraction with phospholipase A2 also caused a small but significant inhibition of the Ca2+/calmodulin-dependent phosphorylation of the same protein. The Ca2+/calmodulin-dependent phosphorylation of other major acceptors, and the basal phosphorylation of a 52-kD acceptor enriched in the vesicle fraction, remained unchanged after cleavage of the membrane phospholipids with phospholipase A2. The significance of the selective effect of phospholipase A2 treatment on endogenous membrane phosphorylation is discussed. 相似文献
85.
86.
Murray B. Isman Peter Proksch Ludger Witte 《Archives of insect biochemistry and physiology》1987,6(2):109-120
The extent of metabolism and excretion of three acetylchromenes (two toxic, one relatively nontoxic) were examined in adult migratory grasshoppers (Melanoplus sanguinipes) following topical administration. Both the total amount excreted (parent plus metabolites) and the proportion of parent compound in the excreta were inversely correlated with contact toxicity. Both toxic and nontoxic acetylchromenes are rapidly absorbed from the cuticle, with maximum excretion of parent and metabolite chromenes from 4 to 8 h posttreatment in each case. Much of the applied compounds (60–80%) apparently remains within the insect, and cannot be recovered by extraction of the insect. Metabolites formed result from simple oxidative and reductive transformations. For all of the compounds tested (including the allatocidin precocene II), the major mode of metabolism results from aliphatic hydroxylation of one of the geminal methyl groups on the chromene. No conjugated metabolites were found in the excreta. 相似文献
87.
The electron transfer resulting from illumination and dark storage of PS II has been studied using EPR signals from several electron carriers. The recombination of D+ (Signal II) and Q−A formed by illumination occurred during dark storage at 77 K and was used to deplete reaction centres of D+. The donor D was then shown to be oxidized in the dark by the S2 state of the oxygen-evolving complex. A slow change which occurred during dark storage of PS II samples was detected using the power saturation characteristics of D. We interpret this effect on D to be an indirect result of a rearrangement of the manganese complex during long-term dark adaptation. A role for D in the stability, protection and perhaps initial manganese binding of the oxygen-evolving complex is suggested. 相似文献
88.
The temperature dependence of S-state transitions in Photosystem II was measured by means of thermoluminescence using two different protocols for low-temperature flash excitation: protocol A, “last flash at low temperature”, and protocol B, “all flashes at low temperature”. Comparison of the temperature-dependence curves obtained by these two protocols revealed a marked difference particular for the three-flash experiments. The difference was attributed to the formation of a low-temperature sensitive precursor state between S2 and S3. The state is formed by two flash illumination given at −5 to −50°C, spontaneously transforms to normal S3 on dark warming, and is not converted to S0 by the 3rd flash. The precursor state was tentatively assigned to an S3 in which H+ release is not completed. 相似文献
89.
We used two different techniques to measure the recovery time of Photosystem II following the transfer of a single electron from P-680 to QA in thylakoid membranes isolated from spinach. Electron transfer in Photosystem II reaction centers was probed first by spectroscopic measurements of the electrochromic shift at 518 nm due to charge separation within the reaction centers. Using two short actinic flashes separated by a variable time interval we determined the time required after the first flash for the electrochromic shift at 518 nm to recover to the full extent on the second flash. In the second technique the redox state of QA at variable times after a saturating flash was monitored by measurement of the fluorescence induction in the absence of an inhibitor and in the presence of ferricyanide. The objective was to determine the time required after the actinic flash for the fluorescence induction to recover to the value observed after a 60 s dark period. Measurements were done under conditions in which (1) the electron donor for Photosystem II was water and the acceptor was the endogenous plastoquinone pool, and (2) Q400, the Fe2+ near QA, remained reduced and therefore was not a participant in the flash-induced electron-transfer reactions. The electrochromic shift at 518 nm and the fluorescence induction revealed a prominent biphasic recovery time for Photosystem II reaction centers. The majority of the Photosystem II reaction centers recovered in less than 50 ms. However, approx. one-third of the Photosystem II reaction centers required a half-time of 2–3 s to recover. Our interpretation of these data is that Photosystem II reaction centers consist of at least two distinct populations. One population, typically 68% of the total amount of Photosystem II as determined by the electrochromic shift, has a steady-state turnover rate for the electron-transfer reaction from water to the plastoquinone pool of approx. 250 e− / s, sufficiently rapid to account for measured rates of steady-state electron transport. The other population, typically 32%, has a turnover rate of approx. 0.2 e− / s. Since this turnover rate is over 1000-times slower than normally active Photosystem II complexes, we conclude that the slowly turning over Photosystem II complexes are inconsequential in contributing to energy transduction. The slowly turning over Photosystem II complexes are able to transfer an electron from P-680 to QA rapidly, but the reoxidation of Q−A is slow (t1/2 = 2 s). The fluorescence induction measurements lead us to conclude that there is significant overlap between the slowly turning over fraction of Photosystem II complexes and PS IIβ reaction centers. One corollary of this conclusion is that electron transfer from P-680 to QA in PS IIβ reaction centers results in charge separation across the membrane and gives rise to an electrochromic shift. 相似文献
90.
Effect on aflatoxin production of competition between wild-type and mutant strains of Aspergillus parasiticus 总被引:4,自引:0,他引:4
K. Ehrlich 《Mycopathologia》1987,97(2):93-96
Co-cultivation of a strain of Aspergillus parasiticus, capable of making aflatoxins, with blocked mutant strains, capable of producing none or only a low level of aflatoxins, reduced the net yield of aflatoxins more than that expected based on spore recovery. Yields of aflatoxins were 8-fold less for a norsolorinic acid-producing strain, 14-fold less for an averantin-producing strain, 6-fold less for an averufin-producing strain, and 21-fold less for a versicolorin A-producing strain when co-cultured in equal amounts with a wild-type strain of Aspergillus parasiticus. Even when the wild-type strain was initially present in 100-fold excess, with two of the mutant strains, reduced aflatoxin production was still observed. 相似文献