Initial investigations into the possible roles of homocitric acid in the biosynthesis and function of the active site cofactor of nitrogenase resulted in the isolation and characterization of the dinuclear vanadium(V) species [K2(H2O)5][(VO2)2(R,S-C7H8O7)2]·H2O ( 1). Complex 1 represents the first synthetic structurally characterized transition metal homocitrate complex and may represent an early mobilized precursor in the biosynthesis of VFeco. Compound 1 was characterized by a variety of physical methods, including X-ray crystallography. Crystal data: space group P * (#2), with a = 10.292 (3) Å, b = 16.663 (3) Å, c = 8.343 (1) Å, α = 95.93 (1)°, β = 105.74 (2)°, γ = 90.86 (2)°, V = 1386 (1) Å3, and Z = 2. The homocitrate ligand is coordinated to the vanadium(V) atoms in a bidentate fashion via the deprotonated bridging hydroxyl group and a carboxylate donor. This unique coordination mode accurately mimics the coordination of homocitrate to the cofactor of nitrogenase.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA Unique Coordination Mode for Citrate and a Transition Metal: K2[V(O)2(C6H6O7)]2.cntdot.4H2ODavid W. Wright, Patricia A. Humiston, William H. Orme-Johnson, and William M. DavisCite this: Inorg. Chem. 1995, 34, 16, 4194–4197Publication Date (Print):August 1, 1995Publication History Published online1 May 2002Published inissue 1 August 1995https://pubs.acs.org/doi/10.1021/ic00120a026https://doi.org/10.1021/ic00120a026research-articleACS PublicationsRequest reuse permissionsArticle Views142Altmetric-Citations51LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

This study evaluated the feasibility of monitoring nitro-genase activity in situ through measurement of N(2) uptake rate (NUR) using off-gas mass spectrometry. Four 50-L cultures of Azotobacter vinelandii were grown aer-obically in nitrogen-free medium to cell densities of 1.0-1.3gL(-1) magnetic-sector mass spectrometer was used to monitor NUR along with other gas exchange rates. The small specific uptake rate (1.2 mmol g(-1) h(-1)) and low cell density were found to lead to a NUR below the measurement accuracy limits under normal conditions. An operating strategy and feed gas mixture (40% O(2), 45% N(2) 15% Ar) were designed to improve the signal-to-noise ratio while maintaining dissolved O(2) and N(2) levels in desired ranges. The fraction of N(2) removed from the air stream was increased approximately 5-fold from 0.2% to 1.0% and the measurement noise was reduced 25-fold from a baseline of +/-5to +/-0.2 mmol L(-1) h(-1). The NUR measurements were compared against in vivo and in vitro acetylene reduction assays as well as on-line cell growth rate measurements. While electron transfer requirements predict an NUR-to-acetylene reduction rate ratio of 0.33, measured ratios for the in vivo and in vitro assays were 0.8 and 0.44, respectively. This suggests that other rate-limiting steps were present in the case of the in vivo assay. In accordance with reports in the literature, no concomitant hydrogen evolution was detected. This is the first reported continuous and direct measurement of NUR in fermentation and demonstrates a novel approach for improving measurement accuracy through rational adjustment of operating conditions. The technique has potential to provide useful insight for development and control of microbial nitrogen fixation processes.(c) John Wiley & Sons, Inc.

Investigation of the aqueous coordination chemistry for citrate and vanadium(V) resulted in the isolation and characterization of K-2[V(O)2(C6H6O7)](2) . 4H(2)O (1) Complex 1 represents the first model of the tricarboxylic acid coordinated to the heteroatom found in the cofactor of nitrogenase and may be relevant to other physiological forms of metabolized vanadium(V). 1 was characterized by elemental analysis, IR, UV-vis, and V-51 NMR spectroscopy, and X-ray crystallography. Complex 1 crystallizes in the space group P2(1)/n (No. 14) with a 9.3205(8) Angstrom, b = 11.739(1) Angstrom, c = 11.913(1) Angstrom, beta = 111.65(1)degrees, V = 1211.4(4) Angstrom(3), and Z = 4. Full-matrix least-squares refinement resulted in residuals of R = 0.041 and R(w) = 0.049. The citrate ligand displays a unique bidentate coordination to the vanadium via the bridging hydroxyl group and a unidentate carboxylate group. The structure is best described as a dimer of two five-coordinate vanadium centers doubly bridged by hydroxyl oxygen atoms.

The molybdenum-iron protein of nitrogenase contains 2 Mo atoms and ca. 28-30 Fe atoms. Approximately 16 Fe atoms belong to the P-clusters, a novel type of iron-sulfur cluster of unknown structure. Mossbauer studies have established that P-clusters are diamagnetic in the semireduced state, P(N). Upon oxidation of the protein with redox dyes such as thionin the state P(OX) is attained. Previous studies have revealed that the low-temperature (less-than-or-equal-to 4.2 K) Mossbauer spectra of P(OX) exhibit magnetic hyperfine patterns even in the absence of external magnetic fields. Such behavior is generally characteristic of a Kramers system, i.e., of a system with an odd number of electrons. The spectra had features typical of those observed for a Kramers doublet with extremely anisotropic g-values (g1 >> g2, g3). Recent Mossbauer and EPR studies of integer spin systems in our laboratory have suggested the possibility that P(OX) may be a very unusual non-Kramers system. Here we report Mossbauer and EPR studies of the proteins from Azotobacter vinelandii (Av1), Clostridium pasteurianum (Cp1), Klebsiella pneumoniae (Kp1), and Xanthobacter autotrophicus (Xa1) which prove that the electronic ground doublet of P(OX) is not a Kramers doublet but rather a nearly degenerate doublet (splitting DELTA) of a system with an even number of electrons. Cp1, Av1, and Kp1 have DELTA less-than-or-equal-to 10(-3) cm-1, and the magnetic patterns observed in the zero-field Mossbauer spectra result from mixing of the two electronic levels by Fe-57 hyperfine interactions (\A(z)\ almost-equal-to 10(-3) cm-1). For Av1 and Kp1 we have observed integer-spin EPR transitions, at g(eff) = 11.9, between two excited-state spin levels at 10-15 cm-1. The ground doublet of Xa1 exhibits an integer-spin resonance at g(eff) = 15.6. Analysis of the Xa1 Mossbauer spectra yields DELTA almost-equal-to 0.010 cm-1. Using this value of DELTA, quantitation of the EPR spectra yielded ca. two spins per MoFe protein for P(OX). The observed g-values suggested that P(OX) of Xa1 has S = 3 or S = 4. However, the ground- and excited-state DELTA-values of Kp1 and Av1 indicate that the electronic ground manifold may not consist of an isolated multiplet with definite spin S. Recognition of P(OX) as a non-Kramers state implies that two electrons are removed from each P-cluster in the transformation P(N) --> P(OX). Since ca. four electrons per MoFe protein are removed and since ca. 16 Fe atoms are involved, it follows that the alphabeta dimer of nitrogenase contains two identical P-clusters and that each cluster has ca. 8 Fe sites. The Mossbauer data are reviewed for a model that considers the P-clusters to consist of two bridged cubanes.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAn EXAFS investigation of Hg(II) binding to mercuric reductase: comparative analysis of the wild-type enzyme and a mutant enzyme generated by site-directed mutagenesisScott A. Raybuck, Mark D. Distefano, Boon Keng Teo, William Orme-Johnson, and Christopher T. WalshCite this: J. Am. Chem. Soc. 1990, 112, 5, 1983–1989Publication Date (Print):February 1, 1990Publication History Published online1 May 2002Published inissue 1 February 1990https://pubs.acs.org/doi/10.1021/ja00161a051https://doi.org/10.1021/ja00161a051research-articleACS PublicationsRequest reuse permissionsArticle Views109Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTwo components of an extracellular protein aggregate of Clostridium thermocellum together degrade crystalline celluloseJ. H. David Wu, William H. Orme-Johnson, and Arnold L. DemainCite this: Biochemistry 1988, 27, 5, 1703–1709Publication Date (Print):March 8, 1988Publication History Published online1 May 2002Published inissue 8 March 1988https://pubs.acs.org/doi/10.1021/bi00405a048https://doi.org/10.1021/bi00405a048research-articleACS PublicationsRequest reuse permissionsArticle Views280Altmetric-Citations114LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIron-57 hyperfine coupling tensors of the FeMo cluster in Azotobacter vinelandii MoFe protein: determination by polycrystalline ENDOR spectroscopyAnne E. True, Mark J. Nelson, Ronald A. Venters, William H. Orme-Johnson, and Brian M. HoffmanCite this: J. Am. Chem. Soc. 1988, 110, 6, 1935–1943Publication Date (Print):March 1, 1988Publication History Published online1 May 2002Published inissue 1 March 1988https://pubs.acs.org/doi/10.1021/ja00214a045https://doi.org/10.1021/ja00214a045research-articleACS PublicationsRequest reuse permissionsArticle Views275Altmetric-Citations68LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

CO dehydrogenase from Clostridium thermoaceticum is a nickel-containing enzyme that catalyzes both the reversible conversion of CO2 to CO (for incorporation into the carbonyl group of acetate) and the synthesis of acetyl-CoA from methyl corrinoid, CO, and CoASH. The latter activity is conveniently assayed by monitoring the exchange of [1-14C]acetyl-CoA (carbonyl group) with 12CO. Kinetic parameters for the highly oxygen sensitive exchange activity have been determined: Km (acetyl-CoA) = 600 microM; Vmax = 440 min-1. In addition, coenzyme A analogues have been tested as inhibitors of the exchange to probe the active site of the enzyme; each has no effect on the CO2 in equilibrium CO activity of CO dehydrogenase. Coenzyme A, the substrate for acetate biosynthesis, is a potent competitive inhibitor, KI = 7 microM. Comparison of this value with that for desulfo-CoA (KI = 6000 microM) suggests that a key mode of binding is through the sulfur atom, possibly to a metal site on the enzyme. The relatively high affinity of the enzyme for CoASH relative to acetyl-CoA is consistent with its proposed operation in the acetogenic direction. The differential sensitivity to oxygen and storage of the two activities of CO dehydrogenase as well as the contrasting effect of coenzyme A inhibitors suggests that acetate assemblage occurs at a site distinct from that for CO dehydrogenation.

Intracellular levels of F390 (AMP and GMP adducts of the 5-deazaflavin cofactor F420) in Methanobacterium thermoautotrophicum were analysed after gasing fermenter cultures with several consecutive cycles of substrate gas and gas mixtures containing 5% oxygen. No F390 was detected in growing cells, hydrogen starved cells and CO2 starved cells prior to O2 contamination. Also, no F390 was found in hydrogen depleted cells after O2 treatment. Exposure of exponentially growing cells and CO2 starved cells to oxygen lead to the formation of F390 species; the increase in the detected amount of F390 was coupled to a decrease of the F420 level. As soon as anaerobiosis was reestablished F390 cofactors were degraded and growth proceeded. Independent of the physiological condition of Methanobacterium thermoautotrophicum methanopterin was formed upon O2 exposure. After normal growth conditions were restored the level of detected methanopterin decreased again.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEXAFS studies of the nitrogenase iron protein from Azotobactor vinelandiiPaul A. Lindahl, Boon Keng Teo, and William H. Orme-JohnsonCite this: Inorg. Chem. 1987, 26, 23, 3912–3916Publication Date (Print):November 1, 1987Publication History Published online1 May 2002Published inissue 1 November 1987https://pubs.acs.org/doi/10.1021/ic00270a018https://doi.org/10.1021/ic00270a018research-articleACS PublicationsRequest reuse permissionsArticle Views107Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

ChemInformVolume 18, Issue 38 Natural Products ChemInform Abstract: Nickel-Containing CO Dehydrogenase Catalyzes Reversible Decarbonylation of Acetyl CoA with Retention of Stereochemistry at the Methyl Group. S. A. RAYBUCK, S. A. RAYBUCK Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorN. R. BASTIAN, N. R. BASTIAN Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorL. D. ZYDOWSKY, L. D. ZYDOWSKY Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorK. KOBAYASHI, K. KOBAYASHI Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorH. G. FLOSS, H. G. FLOSS Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorW. H. ORME-JOHNSON, W. H. ORME-JOHNSON Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorC. T. WALSH, C. T. WALSH Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this author S. A. RAYBUCK, S. A. RAYBUCK Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorN. R. BASTIAN, N. R. BASTIAN Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorL. D. ZYDOWSKY, L. D. ZYDOWSKY Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorK. KOBAYASHI, K. KOBAYASHI Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorH. G. FLOSS, H. G. FLOSS Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorW. H. ORME-JOHNSON, W. H. ORME-JOHNSON Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this authorC. T. WALSH, C. T. WALSH Dep. Chem., Emory Univ., Atlanta, GA 30322, USASearch for more papers by this author First published: September 22, 1987 https://doi.org/10.1002/chin.198738352AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume18, Issue38September 22, 1987 RelatedInformation

ChemInformVolume 18, Issue 9 Organoelement Compounds ChemInform Abstract: Kinetic, Spectroscopic, and Structural (Extended X-Ray Absorption Fine Structure) Studies on the Type 1 Blue Copper Protein Umecyanin. S. K. CHAPMAN, S. K. CHAPMAN Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorW. H. ORME-JOHNSON, W. H. ORME-JOHNSON Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorJ. MCGINNIS, J. MCGINNIS Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorJ. D. SINCLAIR-DAY, J. D. SINCLAIR-DAY Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorA. G. SYKES, A. G. SYKES Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorP.-I. OHLSSON, P.-I. OHLSSON Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorK.-G. PAUL, K.-G. PAUL Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this author S. K. CHAPMAN, S. K. CHAPMAN Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorW. H. ORME-JOHNSON, W. H. ORME-JOHNSON Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorJ. MCGINNIS, J. MCGINNIS Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorJ. D. SINCLAIR-DAY, J. D. SINCLAIR-DAY Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorA. G. SYKES, A. G. SYKES Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorP.-I. OHLSSON, P.-I. OHLSSON Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this authorK.-G. PAUL, K.-G. PAUL Dep. Inorg. Chem., Univ., Newcastle upon Tyne NE1 7RU, UKSearch for more papers by this author First published: March 3, 1987 https://doi.org/10.1002/chin.198709268Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue9March 3, 1987 RelatedInformation

The nature of the ligation of N-methylformamide (NMF) to the metal sites of FeMoco has been investigated. The IR spectrum of FeMoco in NMF shows an intense band at 1600 cm−1 which we assign to the v(CO) stretch of ligated NMF. This frequency is characteristic of N-deprotonated amide ligands, indicating that NMF ligation to FeMoco is predominantly through nitrogen. Hence NMF behaves as an anionic ligand. The importance of the amide functionality for FeMoco extraction has been further examined and a new extracting agent, 2-pyrrolidinone, has been employed. We hypothesize that, in the MoFe-protein, the primary coordination of the cofactor is via deprotonated backbone amide ligands.

The effects of pH variations on the visible spectrum (pKa 9.46 ± 0.04), e.s.r. spectrum, extended X-ray absorption fine structure (EXAFS), and on the reactivity of the blue copper protein umecyanin have been investigated. The electron-transfer reactions of umecyanin have been studied with the complexes [Co(dipic)2]–(dipic = dipicolinate) and [Co(C2O4)3]3– as oxidants for UCu(I), and [Ru(NH3)5(py)]2+(py = pyridine) as a reductant for UCu(II), at 25 °C, I= 0.10 M (NaCl). The oxidation of umecyanin with [Fe(CN)6]3– is extremely rapid, consequently a limited study was carried out at a lower temperature. The oxidation of the protein by [Co(phen)3]3+(phen = 1,10-phenanthroline) was also studied under these conditions for comparison. Of interest are the pKa values observed for the oxidation of umecyanin by [Co(C2O4)3]3–(pKa 9.68 ± 0.08) and the reduction of umecyanin by [Ru(NH3)5(py)]2+(pKa 9.50 ± 0.07). The low temperature (20 K)X-band e.s.r. spectrum of oxidised umecyanin (g‖= 2.32, g⊥= 2.06) shows little variation over the pH range 7.5–10.5. The Cu K-edge EXAFS of umecyanin in both oxidation states and at pH 7.5 and 10.5 were obtained. Analysis of data from the oxidised protein shows the Cu atom has two nitrogen ligands at 1.99 ± 0.03 Å and one sulphur at 2.13 ± 0.02 Å. In the reduced protein the bond lengths increase to 2.03 ± 0.03 Å and 2.21 ± 0.02 Å respectively. There was no detectable difference in co-ordination number or bond lengths at the different pH values, and no fourth ligand could be detected by the EXAFS technique. The results from these various studies are discussed in terms of changes at or near the active site of umecyanin.

Pulsed electron paramagnetic resonance spectroscopy has been used to detect Mn(II)-ligand superhyperfine couplings in complexes with creatine kinase and in the Mn(II) metalloprotein concanavalin A. Electron spin-echo envelopes from Mn(II), bound in these complexes, are modulated by superhyperfine interactions between Mn(II) and nearby, weakly coupled nuclear spins. The characteristic frequencies of the modulations were obtained by Fourier transformation of the three-pulse, spin-echo envelopes. In transition-state analogue complexes of creatine kinase (enzyme-MnIIADP-anion-creatine), superhyperfine interactions from the directly coordinated nitrogen of the thiocyanate ligand give envelope modulations. The source of the modulations was confirmed by measurements with the 14N and 15N forms of thiocyanate. On the other hand, the nitrogen of coordinated nitrate, which is two bonds removed from the paramagnetic center, does not produce detectable modulations. In spectra for Mn(II) concanavalin A, envelope modulations are detected due to the nitrogen of the coordinated histidine residue. Complexes prepared in 2H2O give strong signals due to weakly coupled 2H. For Mn(II)-doped single crystals of sodium pyrophosphate, signals are observed in the frequency domain spectra that are due to coupling from 31P. Phosphorus signals from the ADP ligand in complexes with creatine kinase show approximately the same coupling constant but have a much broader line width.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTENDOR of the resting state of nitrogenase molybdenum-iron proteins from Azotobacter vinelandii, Klebsiella pneumoniae, and Clostridium pasteurianum. Proton, iron-57, molybdenum-95, and sulfur-33 studiesRonald A. Venters, Mark J. Nelson, Paul A. McLean, Anne E. True, Mark A. Levy, Brian M. Hoffman, and William H. Orme-JohnsonCite this: J. Am. Chem. Soc. 1986, 108, 12, 3487–3498Publication Date (Print):June 1, 1986Publication History Published online1 May 2002Published inissue 1 June 1986https://pubs.acs.org/doi/10.1021/ja00272a054https://doi.org/10.1021/ja00272a054research-articleACS PublicationsRequest reuse permissionsArticle Views356Altmetric-Citations80LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts