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291.
Wim F. J. Vermaas Stenbjörn Styring Wolfgang P. Schröder Bertil Andersson 《Photosynthesis research》1993,38(3):249-263
Approximately 20 protein subunits are associated with the PS II complex, not counting subunits of peripheral light-harvesting antenna complexes. However, it is not yet established which proteins specifically are involved in the water-oxidation process. Much evidence supports the concept that the D1/D2 reaction center heterodimer not only plays a central role in the primary photochemistry of Photosystem II, but also is involved in electron donation to P680 and in ligation of the manganese cluster. This evidence includes (a) the primary donor to P680 has been shown to be a redox-active tyrosyl residue (Tyr161) in the D1 protein, and (b) site-directed mutagenesis and computer-assisted modeling of the reaction center heterodimer have suggested several sites with a possible function in manganese ligation. These include Asp170, Gln165 and Gln189 of the D1 protein and Glu69 of the D2 protein as well as the C-terminal portion of the mature D1 protein. Also, hydrophilic loops of the chlorophyll-binding protein CP43 that are exposed at the inner thylakoid surface could be essential for the water-splitting process.In photosynthetic eukaryotes, three lumenal extrinsic proteins, PS II-O (33 kDa), PS II-P (23 kDa) and PS II-Q (16 kDa), influence the properties of the manganese cluster without being involved in the actual catalysis of water oxidation. The extrinsic proteins together may have multiple binding sites to the integral portion of PS II, which could be provided by the D1/D2 heterodimer and CP47. A major role for the PS II-O protein is to stabilize the manganese cluster. Most experimental evidence favors a connection of the PS II-P protein with binding of the Cl- and Ca2+ ions required for the water oxidation, while the PS II-Q protein seems to be associated only with the Cl- requirement. The two latter proteins are not present in PS II of prokaryotic organisms, where their functions may be replaced by a 10–12 kDa subunit and a newly discovered low-potential cytochrome c-550.Abbreviations PS II
Photosystem II
- PCC
Pasteur Culture Collection 相似文献
292.
Peter H. Homann 《Photosynthesis research》1993,38(3):395-400
Under conditions that assured rebinding of the extrinsic 17 and 23 kDa polypeptides, Cl--depleted Photosystem II membranes isolated from spinach chloroplasts were subjected to reconstituting treatments in media containing NaF, NaCl, NaBr, NaI or NaNO3, or they were kept in a medium without any added salt other than the buffer. After removing most of the unbound reconstituting anions by washing, the O2-evolution activities and thermoluminescence properties of the membranes were compared. While the temperature of maximal thermoluminescence emission was lowest for membranes treated with Cl-, no uniform correlation was evident between the temperature profile of the thermoluminescence emission and the apparent activating effectiveness of the anions in the membranes' water oxidizing machinery. However, the differences between the thermoluminescence features did conform to a trend according to which the emission temperatures were upshifted as the size of the activating anion increased, and its hydration energy decreased, i.e. Cl-<Br-<NO3
-<I-. The inactive F- anions were not well retained by the membranes. To explain the experimental data it is suggested that the structural environment of the charge accumulating Mn-center is influenced by the ionic conditions encountered by the Photosystem II membranes after Cl- removal, further enforced by the binding of compatible anions, and then stabilized by the 17 and 23 kDa extrinsic polypeptides. If, as some concepts imply, the anion binding sites are located at or near the functional Mn, only very exceptional characteristics of the water-oxidizing mechanism may account for the observation that the potentially electron-donating I- anion can serve as activator and that it stabilizes rather than destabilizes the S2-state.Abbreviations Chl
chlorophyll
- Hepes
4-(2-hydroxyethyl)-1-piperazine-ethane sulfonic acid
- Mes
2-(N-morpholino)ethane sulfonic acid
- Pheo
the pheophytin a of the Photosystem II reaction center
- PS
photosystem 相似文献
293.
Inorganic cofactors (Mn, Ca2+ and Cl-) are essential for oxidation of H2O to O2 by Photosystem II. The Mn reductants NH2OH and its N-methyl derivatives have been employed as probes to further examine the interactions between these species and Mn at the active site of H2O oxidation. Results of these studies show that the size of a hydroxylamine derivative regulates its ability to inactivate O2 evolution activity, and that this size-dependent inhibition behavior arises from the protein structure of Photosystem II. A set of anions (Cl-, F- and SO4
2-) is able to slow NH2OH and CH3NHOH inactivation of intact Photosystem II membranes by exerting a stabilizing influence on the extrinsic 23 and 17 kDa polypeptides. In contrast to this non-specific anion effect, only Cl- is capable of attenuating CH3NHOH and (CH3)2NOH inhibition in salt-washed preparations lacking the 23 and 17 kDa polypeptides. However, Cl- fails to protect against NH2OH inhibition in salt-washed membranes. These results indicate that the attack by NH2OH and its N-methyl derivatives on Mn occurs at different sites in the O2-evolving complex. The small reductant NH2OH acts at a Cl--insensitive site whereas the inhibitions by CH3NHOH and (CH3)2NOH involve a site that is Cl- sensitive. These findings are consistent with earlier studies showing that the size of primary amines controls the Cl- sensitivity of their binding to Mn in the O2-evolving complex.Abbreviation MES
4-morpholinoethanesulfonic acid
- PS II
Photosystem II 相似文献
294.
Selective solubilization of Photosystem II membranes with the non-ionic detergent octyl thioglucopyranoside has allowed the isolation of a PS II system which has been depleted of the 22 and 10 kDa polypeptides but retains all three extrinsic proteins (33, 23 and 17 kDa). The PS II membranes which have been depleted of the 22 and 10 kDa species show high rates of oxygen evolution activity, external calcium is not required for activity and the manganese complex is not destroyed by exogenous reductants. When we compared this system to control PS II membranes, we observed a minor modification of the reducing side, and a conversion of the high-potential to the low-potential form of cytochrome b
559.Abbreviations Chl-
chlorophyll
- DCBQ-
2,5-dichloro-p-benzoquinone
- DCMU-
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- ESR-
electron spin resonance
- MES-
2-(N-morpholino)ethanesulfonic acid
- OTG-
octyl--d-thioglucopyranoside
- PS II-
Photosystem II
- PEG-
polyethylene glycol, Mr=6000
- Tris-
2-amino-2-hydroxyethylpropane-1,3-diol 相似文献
295.
For phylogenetic analysis of the higher fungi, we sequenced the nuclear small subunit rRNA (18S rRNA) gene fromTaphrina populina, the type species of the genusTaphrina, andProtomyces lactucae-debilis. The molecular phylogeny inferred from these 2 sequences and 75 sequences from the DNA data bank divided the Ascomycota into three major lineages: the hemiascomycetes, the euascomycetes, and the archiascomycetes, newly described herein. The former two lineages are monophyletic, whereas the archiascomycetes, which originated first and are comprised ofTaphrina, Protomyces, Saitoella, Schizosaccharomyces, andPneumocystis, may not be monophyletic. Among the archiascomycetes, theTaphrina/Protomyces branch is monophyletic. Confirmation of the archiascomycetes as a monophyletic taxonomic class will require comparison of additional genetically defined characters.This work was supported in part by grants 05454030 from the Ministry of Education, Science, and Culture of Japan (to J. S.) and 4369 from the Japan Society for the Promotion of Science Fellowship Programs (to H. N.). 相似文献
296.
利用染色体配对分析和酯酶及种子醇溶蛋白电泳分析研究了我国育成的11个八倍体小偃麦,结果表明:(a)来源于小麦和中间偃麦草杂交后代的6个部分双二倍体中,中1和中2的偃麦草染色体组不同于中3、中4、中5和小偃78829的偃麦草染色体组;(b)来源于小麦和长穗偃麦草杂交后代的5个部分双二倍体中,小偃784的偃麦草染色体组不同于小偃693和小偃7631中的偃麦草染色体组,表明在长穗偃麦草中有两个互不相同又不同于小麦的染色体组E和F,而小偃7430和小偃68中的偃麦草染色体组很可能是E和F染色体组的重组体;(c)小偃784中的长穗偃麦草染色体组和中5及小偃78829中的中间偃麦草染色体组基本相同,而中2的中间偃麦草染色体组不同于小偃693和小偃7631中的长穗偃麦草染色体组F,这意味着在长穗偃麦草和中间偃麦草中可能只有一个共同的染色体组E。部分双二倍体中酯酶及醇溶蛋白偃麦草染色体特征带的存在和发现,为这些染色体或其片段导入小麦后的鉴定提供了方便。 相似文献
297.
从印度木薯花叶病毒(ICMV)侵染的植物中纯化特异的核酸,经RNAase,DNAasc,Nucle-aseSl,ExonucleaseⅢ和EcoRI酶切,Southern和Dotblots杂交证实,在感病的植株中,存在两种形式的病毒核酸:环状双链DNA和环状单链DNA,后者可能是病毒DNA的(-)链,环状双链DNA经限制性内切酶作用可得2.7kb的线性双链DNA纯化的病毒核酸含DNA1和DNA2两个分子量相近的组份。 相似文献
298.
This paper presents a simple model for the evolution of reaction norms for age and size at maturity that predicts reaction norms with a variety of shapes. Using realistic parameter values the model predicts reaction norms close to those observed in Drosophila. The major assumptions of the model are: 1) that net reproductive rate is maximized, 2) that growth is determinate, and 3) that mortality rates are independent of age and size at maturity. If, additionally, juvenile mortality is uncorrelated with a growth coefficient, k, the model predicts that selection favors maturation later at a smaller size when k is reduced by environmental factors and that decreased juvenile mortality leads to delayed maturity. These two predictions conform with those found by previous models using other measures of fitness. Correlations between k and juvenile mortality can change the shape of the predicted reaction norm. Depending on the precise form of the correlation, the model can predict done- or bowl-shaped reaction norms and can predict delayed or earlier maturity as k decreases. These shapes are qualitatively different from those predicted by previous models that used different fitness measures. Systematic estimates of the parameter values for this and for related models are required to determine the appropriate fitness measure for models of reaction norms. 相似文献
299.
300.
Esterina Pascale Christine Liu Eulalia Valle Karen Usdin Anthony V. Furano 《Journal of molecular evolution》1993,36(1):9-20
Summary All modern mammals contain a distinctive, highly repeated (⩾50,000 members) family of long interspersed repeated DNA called
the L1 (LINE 1) family. While the modern L1 families were derived from a common ancestor that predated the mammalian radiation
∼80 million years ago, most of the members of these families were generated within the last 5 million years. However, recently
we demonstrated that modern murine (Old World rats and mice) genomes share an older long interspersed repeated DNA family
that we called Lx. Here we report our analysis of the DNA sequence of Lx family members and the relationship of this family
to the modern L1 families in mouse and rat. The extent of DNA sequence divergence between Lx members indicates that the Lx
amplification occurred about 12 million years ago, around the time of the murine radiation. Parsimony analysis revealed that
Lx elements were ancestral to both the modern rat and mouse L1 families. However, we found that few if any of the evolutionary
intermediates between the Lx and the modern L1 families were extensively amplified. Because the modern L1 families have evolved
under selective pressure, the evolutionary intermediates must have been capable of replication. Therefore, replicationcompetent
L1 elements can reside in genomes without undergoing extensive amplification. We discuss the bearing of our findings on the
evolution of L1 DNA elements and the mammalian genome. 相似文献