EXAFS of Klebsiella pneumoniae nitrogenase MoFe protein from wild-type and nif V mutant strains

Abstract

ing to trapped silylene (22, 24) or silanone (23) was found. An even smaller amount of 7 (<2%) was identified by GCMS. When compared with the results of copyrolysis of 7 with excess dimethyldimethoxysilane (vide supra) under the same conditions, many of the numerous unidentified compounds formed can be attributed to redistribution reactions. No attempt was made to isolate the presumed trapping product or to provide positive identification of the redistribution products.Copyrolysis of 21 with 1,3-Butadiene. Trisilane 21 (0.3448 g, 1.2 X mol) was pyrolyzed in a vertical flow system with 1,3-butadiene as the carrier gas. At 510 "C (35 mL/min butadiene flow rate), a mass recovery (after evaporation of volatiles) of 46% was obtained. No compound of m / e 212 (corresponding to silylene trapping product) was found by GCMS.Acknowledgment. The support of this work by the National Registry No.

The vanadium-iron protein of vanadium nitrogenase from Azotobacter chroococcum contains an iron-vanadium cofactor

“…* To whom correspondence should be addressed. 2, Lowe et al (1985); 3, Eady (1986); 4, Shah & Brill (1977);5, Yang et al (1982);6, Eady et al (1980); 7, Eidsness et al (1986);8, Newton et al (1985). Abbreviation: e.x.a.f.s., extended X-ray-absorption fine structure.…”

Iron K-edge X-ray absorption spectroscopy of the iron-molybdenum cofactor of nitrogenase from Klebsiella pneumoniae

“…Other evidence (Lowe et al, 1985) demonstrates that molybdenum is an integral part of FeMoco and, consistent with the molybdenum K-edge e.x.a.f.s. results (Cramer et al, 1978a,b;Eidsness et al, 1986;Flank et al, 1986;Flood, 1986), we have included (Table 1) back-scattering from molybdenum for at least some of the iron atoms. The contribution from molybdenum back-scattering is nearly out of phase with that of iron in the low k region of the spectrum, and the effect of this smaller molybdenum back-scattering contribution can be partially compensated for by a slightly shorter Fe ... Fe distance (about 0.262 nm).…”

“…Most X-ray-absorption studies of nitrogenase have focused on the environment of molybdenum in the MoFe protein and in FeMoco extracted into NMF, and the interpretations of the extended X-ray-absorption-fine structure (e.x.a.f.s.) data imply that molybdenum has three or four sulphur atoms at 0.24 nm, two to four iron atoms at 0.27 nm and, possibly, one or two oxygen or nitrogen atoms at 0.22 nm in its immediate environment (Cramer et al, 1978a,b;Eidsness et al, 1986;Flank et al, 1986;Flood, 1986). A recent analysis of molybdenum K-edge X-ray absorption near edge structure (x.a.n.e.s.)…”

Metalloprotein active site structure determination: Synergy between X-ray absorption spectroscopy and X-ray crystallography

“…One recent example is the probable observation of an iodide bound within a basic pocket at~5 Å from the metal site in the molybdenum enzyme sulfite oxidase [32]. An earlier example is the observation of a weak interaction observed as a Fourier transform peak at about 5 Å in the Mo EXAFS of nitrogenase [33], which is particularly noticeable in its isolated cofactor [34]. This 5 Å peak arises from three distant irons [35] and the difference in intensity from the transform peak at~2.7 Å arising from three closer irons nicely illustrates the distance limitations of EXAFS (Fig.…”