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11.
J. Telser H. -I. Lee E. T. Smith H. Huang P. Brereton M. W. W. Adams R. C. Conover M. K. Johnson B. M. Hoffman 《Applied magnetic resonance》1998,14(2-3):305-321
The hyperthermophilic archaeonPyrococcus furiosus contains a four-Fe ferredoxin (Pf- Fd) that differs from most other 4Fe-Fd’s in that its [Fe4S4] cluster is anchored to protein by only three cysteinyl residues.Pf- Fd also is of interest because in its reduced form, [Fe4S4]+, the cluster exhibits bothS = 1/2 andS = 3/2 spin states. Addition of excess cyanide ion converts the cluster exclusively to anS = 1/2 state (g1 = 2.09, g2 = 1.95, g3 = 1.92), however dialysis restores the EPR signal of native reduced protein indicating that the cluster is not irreversibly altered by cyanide. Both the native protein and protein in the presence of excess cyanide ion (Pf- Fd 4Fe-CN) were investigated here using the techniques of electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. In particular,Pf- Fd 4Fe-CN was investigated using13CN? and C15N? ligands.13C and15N ENDOR indicated that a single cyanide ion bound directly, with the cluster showing an unusually small contact interaction (aiso(13C)~ ?3 MHz, aiso(15N) ~ 0). This is in contrast to cyanide bound to monomeric low-spin Fe(III)-containing proteins such as transferrin and myoglobin, for which the13C hyperfine coupling has a large isotropic component (aiso(13C) ≈ ?30 MHz). This small contact interaction is not due to low spin density of Fe, as57Fe ENDOR of the singly and triply labeledPf- Fd 4FeCN isotopologs, [57FeFe3S4]+ and [Fe57Fe3S4]+, show hyperfine coupling characteristic for [Fe4S4]+ clusters, particularly for the Fe to which cyanide binds. Thus, the low spin density on13C is not due to low spin density on the Fe ion to which it binds. Further theoretical work is needed to explain the contrast between the strong electronic effect of cyanide ion binding with the low spin density on the ligand. 相似文献
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Grosnick D Wright SC Bolton RD Cooper MD Frank JS Hallin AL Heusi PA Hoffman CM Hogan GE Mariam FG Matis HS Mischke RE Piilonen LE Sandberg VD Sanders GH Sennhauser U Werbeck R Williams RA Wilson SL Hofstadter R Hughes EB Ritter MW Highland VL McDonough J 《Physical review letters》1986,57(26):3241-3244
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During the reaction of cadmium sulfide with erbium and sulfur in evacuated silica ampoules pink lath‐shaped crystals of Er2S[SiO4] occur as by‐product which were characterized by X‐ray single crystal structure analysis. The title compound crystallizes orthorhombically in the space group Cmce (a = 1070.02(8), b = 1235.48(9), c = 683.64(6) pm) with eight formula units per unit cell. Besides isolated ortho‐oxosilicate units [SiO4]4?, the crystal structure contains two crystallographically independent Er3+ cations which are both eightfold coordinated by six oxygen and two sulfur atoms. The sulfide anions are surrounded by four erbium cations each in the shape of very distorted tetrahedra. These excentric [SEr4]10+ tetrahedra build up layers according to by vertex‐ and edge‐connection. They are piled parallel to (010) and separated by the isolated ortho‐oxosilicate tetrahedra. 相似文献
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Leva S Lichte A Burmeister J Muhn P Jahnke B Fesser D Erfurth J Burgstaller P Klussmann S 《Chemistry & biology》2002,9(3):351-359
Mirror-image oligonucleotide ligands (Spiegelmers) that bind to the pharmacologically relevant target gonadotropin-releasing hormone I (GnRH) with high affinity and high specificity have been identified using the Spiegelmer technology. GnRH is a decapeptide that plays an important role in mammalian reproduction and sexual maturation and is associated with several benign and malignant diseases. First, aptamers that bind to D-GnRH with dissociation constants of 50-100 nM were isolated out of RNA and DNA libraries. The respective enantiomers of the DNA and RNA aptamers were synthesized, and their binding to L-GnRH was shown. These Spiegelmers bind to L-GnRH with similar affinity to that of the corresponding aptamers that bind to D-GnRH. We further demonstrated dose-dependent inhibition of GnRH-induced Ca(2+) release in Chinese hamster ovary cells that were stably transfected with the human GnRH receptor. 相似文献
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Pressure-supported packed capillary electrochromatography (CEC) and packed capillary high-performance liquid chromatography (pHPLC) have been coupled on-line to electrospray ionization-mass spectrometry (ESI-MS) and coordination ion spray-mass spectrometry (CIS-MS). Separation of enantiomers of barbiturates and chlorinated alkyl phenoxypropanoates were performed on a permethylated beta-cyclodextrin stationary phase by pressure-supported CEC. For on-line detection with ESI- and CIS-MS, a modified sheath-liquid interface was used. CIS-MS is a universal, novel ionization technique which improves the selectivity as well as the sensitivity. Charged complexes were formed through the addition of central complexing ions such as silver(I), cobalt(II), copper(II), and lithium(I) to the sheath flow. Advantages of CIS-MS detection compared to the ESI-MS mode are discussed. In the CIS-MS mode, increased sensitivity and high selectivity was attained through different possibilities of complexation. The superiority of pressure-supported CEC compared to pHPLC in the hyphenation with CIS-MS is demonstrated. 相似文献