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排序方式: 共有152条查询结果,搜索用时 31 毫秒
1.
Salil K. Niyogi Thomas S. Soper Robert S. Foote Frank W. Larimer Richard J. Mural Sankar Mitra Eva H. Lee Richard Machanoff Fred C. Hartman 《Journal of biosciences》1987,11(1-4):203-214
Both Lys-166 and His-291 of ribulosebisphosphate carboxylase/oxygenase fromRhodospirillum rubrum have been implicated as the active-site residue that initiates catalysis. To decide between these two candidates, we resorted
to site-directed mutagenesis to replace Lys-166 and His-291 with several amino acids. All 7 of the position-166 mutants tested
are severely deficient in carboxylase activity, whereas the alanine and serine mutants at position 291 are ∼40% and ∼18% as
active as the native carboxylase, essentially ruling out His-291 in theRhodospirillum rubrum carboxylase (and by inference His-298 in the spinach enzyme) as a catalytically essential residue. The ability of some of
the mutant proteins to undergo carbamate formation or to bind either ribulosebisphosphate or a transition-state analogue remains
largely unimpaired. This implies that Lys-166 is not required for substrate binding; rather, the results corroborate the earlier
postulate that Lys-166 functions as an acid-base group in catalysis or in stabilizing a transition state in the reaction pathway. 相似文献
2.
Aromaticity at position 37 in human epidermal growth factor is not obligatory for activity. 下载免费PDF全文
The third disulfide loop (amino acids 33 to 42) of human epidermal growth factor (hEGF) encompasses the region of highest amino acid conservation among all of the EGF-like family of molecules. The importance of some of these highly conserved residues for the maintenance of biological activity, especially the aromatic amino acid tyrosine at position 37, has until now been considered essential on the basis of previous studies with the EGF-like molecule transforming growth factor alpha. Variants at the Tyr-37 position of hEGF were constructed by site-directed mutagenesis. The substituting amino acids were phenylalanine, histidine, serine, alanine, aspartic acid, arginine, and glycine. The variants were tested for their ability to competitively displace native [125I]hEGF from its receptor and to stimulate the protein-tyrosine kinase activity of the receptor; the order of efficacy of substituting amino acids was Phe greater than His greater than Ser greater than Ala greater than Asp greater than Arg greater than Gly in both assays. All were effective, with no or only moderate reduction in potency, in stimulating the incorporation of [3H]thymidine into acid-insoluble material of quiescent mouse A31 cells. Only Tyr-37----Ala, Tyr-37----Arg and Tyr-37----Gly were slightly less potent in the cell assay. Thus, neither tyrosine nor another aromatic amino acid at position 37 in hEGF is essential for full biological activity. 相似文献
3.
Lauffenburger DA Chu L French A Oehrtman G Reddy C Wells A Niyogi S Wiley HS 《Biotechnology and bioengineering》1996,52(1):61-80
Peptide growth factors and other receptor-binding cytokine ligands are of interest in contemporary molecular health care approaches in applications such as wound healing, tissue regeneration, and gene therapy. Development of effective technologies based on operation of these regulatory molecules requires an ability to deliver the ligands to target cells in a reliable and well-characterizable manner. Quantitative information concerning the fate of peptide ligands within tissues is necessary for adequate interpretation of experimental observations at the tissue level and for truly rational engineering design of ligand-based therapies. To address this need, we are undertaking efforts to elucidate effects of key molecular and cellular parameters on temporal and spatial distribution of cytokines in cell population and cell/matrix systems. In this article we summarize some of our recent findings on dynamics of growth factor depletion by cellular endocytic trafficking, growth factor transport through cellular matrices, and growth factor production and release by autocrine cell systems. (c) 1996 John Wiley & Sons, Inc. 相似文献
4.
Site-directed mutagenesis was employed to examine the function of two highly conserved residues, Tyr-37 and Arg-41, of human EGF (hEGF) in receptor binding. Both a conservative change to phenylalanine and a semi-conservative change to histidine at position 37 yield proteins with receptor affinity similar to wild-type hEGF. A non-conservative change to alanine results in a molecule with about 40% of the receptor affinity, indicating that an aromatic residue is not essential at this position. Both conservative (to lysine) and non-conservative (to alanine) substitutions at position 41 drastically reduced receptor binding to less than 0.5% of the wild-type activity. 1D-NMR data indicate that the replacement of Arg-41 by lysine does not significantly alter the native protein conformation. Thus, Arg-41 may be directly involved in ligand receptor interaction, whereas the side chain of Tyr-37, although possibly important structurally, is not essential for receptor binding. 相似文献
5.
6.
Guillaume Allorent Ryutaro Tokutsu Thomas Roach Graham Peers Pierre Cardol Jacqueline Girard-Bascou Daphné Seigneurin-Berny Dimitris Petroutsos Marcel Kuntz Cécile Breyton Fabrice Franck Francis-André Wollman Krishna K. Niyogi Anja Krieger-Liszkay Jun Minagawa Giovanni Finazzi 《The Plant cell》2013,25(2):545-557
Absorption of light in excess of the capacity for photosynthetic electron transport is damaging to photosynthetic organisms. Several mechanisms exist to avoid photodamage, which are collectively referred to as nonphotochemical quenching. This term comprises at least two major processes. State transitions (qT) represent changes in the relative antenna sizes of photosystems II and I. High energy quenching (qE) is the increased thermal dissipation of light energy triggered by lumen acidification. To investigate the respective roles of qE and qT in photoprotection, a mutant (npq4 stt7-9) was generated in Chlamydomonas reinhardtii by crossing the state transition–deficient mutant (stt7-9) with a strain having a largely reduced qE capacity (npq4). The comparative phenotypic analysis of the wild type, single mutants, and double mutants reveals that both state transitions and qE are induced by high light. Moreover, the double mutant exhibits an increased photosensitivity with respect to the single mutants and the wild type. Therefore, we suggest that besides qE, state transitions also play a photoprotective role during high light acclimation of the cells, most likely by decreasing hydrogen peroxide production. These results are discussed in terms of the relative photoprotective benefit related to thermal dissipation of excess light and/or to the physical displacement of antennas from photosystem II. 相似文献
7.
Under high-light conditions, photoprotective mechanisms minimize the damaging effects of excess light. A primary photoprotective mechanism is thermal dissipation of excess excitation energy within the light-harvesting complex of photosystem II (LHCII). Although roles for both carotenoids and specific polypeptides in thermal dissipation have been reported, neither the site nor the mechanism of this process has been defined precisely. Here, we describe the physiological and molecular characteristics of the Chlamydomonas reinhardtii npq5 mutant, a strain that exhibits little thermal dissipation. This strain is normal for state transition, high light-induced violaxanthin deepoxidation, and low light growth, but it is more sensitive to photoinhibition than the wild type. Furthermore, both pigment data and measurements of photosynthesis suggest that the photosystem II antenna in the npq5 mutant has one-third fewer light-harvesting trimers than do wild-type cells. The npq5 mutant is null for a gene designated Lhcbm1, which encodes a light-harvesting polypeptide present in the trimers of the photosystem II antennae. Based on sequence data, the Lhcbm1 gene is 1 of 10 genes that encode the major LHCII polypeptides in Chlamydomonas. Amino acid alignments demonstrate that these predicted polypeptides display a high degree of sequence identity but maintain specific differences in their N-terminal regions. Both physiological and molecular characterization of the npq5 mutant suggest that most thermal dissipation within LHCII of Chlamydomonas is dependent on the peripherally associated trimeric LHC polypeptides. 相似文献
8.
Baroli I Niyogi KK 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2000,355(1402):1385-1394
The involvement of excited and highly reactive intermediates in oxygenic photosynthesis inevitably results in the generation of reactive oxygen species. To protect the photosynthetic apparatus from oxidative damage, xanthophyll pigments are involved in the quenching of excited chlorophyll and reactive oxygen species, namely 1Chl*, 3Chl*, and 1O2*. Quenching of 1Chl* results in harmless dissipation of excitation energy as heat and is measured as non-photochemical quenching (NPQ) of chlorophyll fluorescence. The multiple roles of xanthophylls in photoprotection are being addressed by characterizing mutants of Chlarnydomonas reinhardtii and Arabidopsis thaliana. Analysis of Arabidopsis mutants that are defective in 1Chl* quenching has shown that, in addition to specific xanthophylls, the psbS gene is necessary for NPQ. Double mutants of Chlamydomonas and Arabidopsis that are deficient in zeaxanthin, lutein and NPQ undergo photo-oxidative bleaching in high light. Extragenic suppressors of the Chlamydomonas npq1 lor1 double mutant identify new mutations that restore varying levels of zeaxanthin accumulation and allow survival in high light. 相似文献
9.
Arabidopsis mutants define a central role for the xanthophyll cycle in the regulation of photosynthetic energy conversion. 总被引:9,自引:1,他引:8 下载免费PDF全文
A conserved regulatory mechanism protects plants against the potentially damaging effects of excessive light. Nearly all photosynthetic eukaryotes are able to dissipate excess absorbed light energy in a process that involves xanthophyll pigments. To dissect the role of xanthophylls in photoprotective energy dissipation in vivo, we isolated Arabidopsis xanthophyll cycle mutants by screening for altered nonphotochemical quenching of chlorophyll fluorescence. The npq1 mutants are unable to convert violaxanthin to zeaxanthin in excessive light, whereas the npq2 mutants accumulate zeaxanthin constitutively. The npq2 mutants are new alleles of aba1, the zeaxanthin epoxidase gene. The high levels of zeaxanthin in npq2 affected the kinetics of induction and relaxation but not the extent of nonphotochemical quenching. Genetic mapping, DNA sequencing, and complementation of npq1 demonstrated that this mutation affects the structural gene encoding violaxanthin deepoxidase. The npq1 mutant exhibited greatly reduced nonphotochemical quenching, demonstrating that violaxanthin deepoxidation is required for the bulk of rapidly reversible nonphotochemical quenching in Arabidopsis. Altered regulation of photosynthetic energy conversion in npq1 was associated with increased sensitivity to photoinhibition. These results, in conjunction with the analysis of npq mutants of Chlamydomonas, suggest that the role of the xanthophyll cycle in nonphotochemical quenching has been conserved, although different photosynthetic eukaryotes rely on the xanthophyll cycle to different extents for the dissipation of excess absorbed light energy. 相似文献