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21.
PvdD, a nonribosomal peptide synthetase (NRPS) of Pseudomonas aeruginosa PAO1, incorporates two L-threonines into the siderophore pyoverdine. A pvdD mutant did not synthesize pyoverdine and lacked a high Mr iron-regulated cytoplasmic protein (IRCP). Analysis of other IRCPs and the P. aeruginosa genome enabled the remaining pyoverdine NRPSs to be identified. The pvdD mutation could be complemented in trans, enabling design of plasmid-based systems for the generation of novel pyoverdines. Introduction of a truncated pvdD gene resulted in attenuated forms of pyoverdine, and introduction of L-threonine-incorporating NRPSs from other organisms restored pyoverdine production to mutant cells. This is the first successful rational in vivo modification of NRPS modules outside of Bacillus subtilis. The systems employed did not allow incorporation of other residues into pyoverdine, indicating that there are multiple elements contributing toward substrate specificity in NRPSs. 相似文献
22.
A tetraketide synthase containing a loading module (LM), the extension modules erythromycin module 1, rapamycin module 2, and erythromycin module 2 (LM-Ery1-Rap2-Ery2-TE), when expressed in Saccharopolyspora erythraea strain JC2, produced as previously reported a mixture of tetraketide lactones (minor products) and triketide lactones (major products). Several alternative plausible mechanisms by which this "skipping" phenomenon might occur may be proposed. Site-directed mutagenesis of the ketosynthase (KS) and acylcarrier protein (ACP) domains in the interpolated module has shown that skipping within the hybrid PKS involves passage of the growing polyketide through the interpolated module, by direct ACP-to-ACP transfer of the polyketide chain. 相似文献
23.
Summary Dissolved SO2 reacts rapidly with [Co([16]aneN5)OH]2+ to give [Co([16]aneN5OSO2]+([16]aneN5=1,4,7,10, 13-penta-azacyclohexadecane), which on immediate acidification loses SO2 to give [Co([16]aneN5)OH2]3+. The O-bonded sulphito complex (max 526 nm) undergoes a slow linkage isomerisation to give the S-bonded species [Co([16]aneN5)SO3]+ (max 466 nm), rather than an internal redox reaction. The S-bonded complex has been isolated and characterised as the perchlorate salt [Co([16]aneN5) (SO3H)](ClO4)2. 相似文献
24.
Gerard de Leeuw John S. Field Raymond J. Haines Beth McCulloch Elsie Meintjies Christiaan Monberg Gillian M. Olivier Praveen Ramdial Clifford N. Sampson Beate Sigwarth Nick D. Steen Kandasamy G. Moodley 《Journal of organometallic chemistry》1984,275(1):99-111
Reaction of [Fe2(CO)9] with a half molar amount of R2PYPR2 (Y = CH2, R = Ph, Me, OMe or OPri; Y = N(Et), R = OPh, OMe or OCH2; Y = N(Me), R = OPri or OEt) leads to the ready formation of a product which on irradiation with ultraviolet light rapidly decarbonylates to the heptacarbonyl derivative [Fe2(μ-CO)(CO)6{μ-R2PYPR2}]. Treatment of the latter with a slight excess of the appropriate ligand results, under photochemical conditions, in the formation of the dinuclear pentacarbonyl complex [Fe2(μ-CO)(C))4{μ-R2PYPR2}2] but under thermal conditions in the formation of the mononuclear species [Fe(CO)3{R2PYPR2}]. Reaction of [Ru3(CO)12] with an equimolar amount of (RO)2PN(R′)P(OR)2 (R′ = Me, R = Pri or Et; R′ = Et, R = Ph or Me) under either thermal or photochemical conditions produces [Ru3(CO)10{μ-(RO)2PN(OR)2}] which reacts further with excess (RO)2PN(R′)P(OR)2 on irradiation with ultraviolet light to afford the dinuclear compound [Ru2(μ-CO)(CO4{μ-(RO)2PN(R′)P(OR)2}2]. The molecular structure of [Ru2(μ-CO)(CO)4{μ-(MeO)2PN(Et)P(OMe)2}2], which has been determined by X-ray crystallography, is described. 相似文献
25.
McColl IH Blanch EW Gill AC Rhie AG Ritchie MA Hecht L Nielsen K Barron LD 《Journal of the American Chemical Society》2003,125(33):10019-10026
The vibrational Raman optical activity (ROA) spectrum of a polypeptide in a model beta-sheet conformation, that of poly(l-lysine), was measured for the first time, and the alpha-helix --> beta-sheet transition monitored as a function of temperature in H(2)O and D(2)O. Although no significant population of a disordered backbone state was detected at intermediate temperatures, some side chain bands not present in either the alpha-helix or beta-sheet state were observed. The observation of ROA bands in the extended amide III region assigned to beta-turns suggests that, under our experimental conditions, beta-sheet poly(L-lysine) contains up-and-down antiparallel beta-sheets based on the hairpin motif. The ROA spectrum of beta-sheet poly(L-lysine) was compared with ROA data on a number of native proteins containing different types of beta-sheet. Amide I and amide II ROA band patterns observed in beta-sheet poly(L-lysine) are different from those observed in typical beta-sheet proteins and may be characteristic of an extended flat multistranded beta-sheet, which is unlike the more irregular and twisted beta-sheet found in most proteins. However, a reduced isoform of the truncated ovine prion protein PrP(94-233) that is rich in beta-sheet shows amide I and amide II ROA bands similar to those of beta-sheet poly(L-lysine), which suggests that the C-terminal domain of the prion protein is able to support unusually flat beta-sheets. A principal component analysis (PCA) that identifies protein structural types from ROA band patterns provides a useful representation of the structural relationships among the polypeptide and protein states considered in the study. 相似文献
26.
Hodgson DM Buxton TJ Cameron ID Gras E Kirton EH 《Organic & biomolecular chemistry》2003,1(23):4293-4301
Enantioselective alpha-deprotonation of achiral epoxides 1, 21, and 26 using organolithiums in the presence of (-)-sparteine 2 and subsequent electrophile trapping gives access to enantioenriched trisubstituted epoxides 9-17, 22, 23, 27 and 28 (in up to 86% ee). 相似文献
27.
McColl IH Blanch EW Hecht L Barron LD 《Journal of the American Chemical Society》2004,126(26):8181-8188
A vibrational Raman optical activity (ROA) study, supplemented by protein X-ray crystal structure data, of alpha-helices in polypeptides, proteins, and viruses has suggested that ROA bands in the extended amide III spectral region may be used to distinguish between two types of right-handed alpha-helix. One type, associated with a positive ROA band at approximately 1300 cm(-1), dominates in hydrophobic environments and appears to be unhydrated; the other, associated with a positive ROA band at approximately 1340 cm(-1), dominates in hydrophilic environments and appears to be hydrated. Evidence is presented to support the hypothesis that unhydrated alpha-helix corresponds to the canonical conformation alpha(c) and hydrated alpha-helix to a more open conformation alpha(o) stabilized by hydrogen bonding of a water molecule or a hydrophilic side chain to the peptide carbonyl. Alpha-helical poly(L-lysine) and poly(L-ornithine) in aqueous solution and poly(L-alanine) in dichloracetic acid display both bands, but alpha-helical poly(l-glutamic acid) in aqueous solution and poly(gamma-benzyl L-glutamate) in CHCl(3) display only the approximately 1340 cm(-1) band and so may exist purely as alpha(o) due to enhanced stabilization of this conformation by particular side chain characteristics. The ROA spectrum of poly(beta-benzyl L-aspartate) in CHCl(3) reveals that it exists in a single left-handed alpha-helical state more analogous to alpha(o) than to alpha(c). 相似文献
28.
David Littlejohn Iain S. Duncan James B.M. Hendry John Marshall John M. Ottaway 《Spectrochimica Acta Part B: Atomic Spectroscopy》1985,40(10-12)
The analytical performance of three uncoated electrographite tubes, three pyro-coated electrographite tubes, one tantalum carbide (TaC) coated electrographite tube, and three totally pyrolytic graphite (TPG) tubes has been evaluated and compared. A test programme was devised to determine the useful operational lifetime of each tube, and assess the influence of tube age on the sensitivity of lead, manganese and vanadium measurements by atomic absorption spectrometry. The TPG tubes were found to be more durable than the other types studied, but the lifetime advantage depended on the thickness of the pyrolytic graphite. The best TPG tube, of 720 μm wall-thickness, lasted 2.5 times longer than the pyro-coated tubes, and 5 times longer than the uncoated electrographite tubes.The TPG tubes gave slightly poorer AAS sensitivity for lead, equivalent sensitivity for manganese, and 4 times better sensitivity for vanadium than the pyro-coated electrographite tubes. Also, with TPG, signal magnitude was more consistent throughout the lifetime of a tube. For each of the test elements studied, poorest sensitivity was encountered with the TaC-coated electrographite tube. 相似文献
29.
M. McCulloch S. K. Fadeff G. M. Mong R. G. Riley D. S. Sklarew B. L. Thomas 《International journal of environmental analytical chemistry》2013,93(2-4):289-293
Abstract DOE Methods for Evaluating Environmental and Waste Management Samples (DOE Methods) is a guidance/methods document to support sampling and analysis activities at DOE sites. DOE Methods is intended to supplement existing guidance documents (e.g., EPA's Test Methods for Evaluating Solid Waste, SW-846), which generally apply to low-level or nonradioactive samples. DOE Methods targets the complexities of DOE radioactive mixed waste and environmental samples. The document contains quality assurance (QA), quality control (QC), safety, sampling, organic analysis, inorganic analysis, and radioanalytical guidance as well as sampling and analytical methods. An addendum is distributed every six months (April and October) with updated guidance and additional methods. DOE Methods provides a vehicle for technology transfer within the environmental restoration (ER) and waste management (WM) (collectively known as EM) community. As DOE Methods evolves, its usefulness and applicability are anticipated to grow to meet the demands of the DOE/EM mission. At the present time, DOE Methods contains methods and guidance information supplied by DOE sites. Because the EM activities in DOE are not unique to the United States, the international environmental community could benefit from the information gathered for the DOE program. This information could provide additional resources for their EM activities. 相似文献
30.