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
Steroid-induced difference spectra have been used to examine the combination of cholesterol with adrenal mitochondrial cytochrome P-450 which participates in cholesterol side chain cleavage (P-450scc) and the depletion of cholesterol from the cytochrome which results from turnover of the enzyme system. Type I difference spectra-induced by cholest-5-ene-3beta, 25-diol (25-hydroxycholesterol) and cholest-5-ene-3beta, 20 alpha, 22R-triol (20alpha, 22R dihydroxycholesterol) have been used to quantitate binding of cholesterol to two sites (I and II) on cytochrome P-450scc. The action of adrenocorticotropic hormone (ACTH) in vivo and the action of calcium or phosphate ions on isolated mitochondria stimulate the combination of cholesterol with site I but not site II. Cholesterol derived from lecithin-cholesterol micelles, however, binds to both sites. Malate-induced cholesterol depletion occurred at a comparable rate to the transfer of cholesterol from lecithin-cholesterol micelles. However, a residual proportion of cholesterol-cytochrome P-450scc complexes remained, even after 10 min of exposure to malate, and was of similar magnitude in mitochondria from both cycloheximide-treated and stressed rats. It is suggested that this reflects a less reactive form of cholesterol-cytochrome complex. Steroid-induced difference spectra indicate that sites I and II on cytochrome P-450scc are similarly depleted after metabolism of mitochondrial cholesterol in vitro and after inhibition of the action of ACTH in vivo. Anaerobiosis of adrenal cells after excision of the accumulation of cholesterol at cytochrome P-450cc. When anaerobiosis was prevented, cytochrome P-450scc in the freshly isolated mitochondria was apparently essentially free of complexed cholesterol, irrespective of the extent of ACTH action. For 30 min after suspension of the mitochondria in 0.25 M sucrose at 4 degrees, cholesterol combines with cytochrome P-450scc. The extent of this process was not affected by the presence of cycloheximide during ether stress treatment of the rats. It is concluded that there are at least two pools of mitochondrial cholesterol with access to cytochrome P-450scc but that ACTH stimulates only the pool which most readily interacts with the cytochrome.
A binary plasmid system was used to produce nitrogenase components in Escherichia coli and subsequently to define a minimum set of nitrogen fixation (nif) genes required for the production of the iron-molybdenum cofactor (FeMoco) reactivatable apomolybdenum-iron (apoMoFe) protein of nitrogenase. The active MoFe protein is an alpha 2 beta 2 tetramer containing two FeMoco clusters and 4 Fe4S4 P centers (for review see, Orme-Johnson, W.H. (1985) Annu. Rev. Biophys. Biophys. Chem. 14, 419-459). The plasmid pVL15, carrying a tac-promoted nifA activator gene, was coharbored in E. coli with the plasmid pGH1 which contained nifHDKTYENXUSVWZMF' derived from the chromosome of the nitrogen fixing bacterium Klebsiella pneumoniae. The apoMoFe protein produced in E. coli by pGH1 + VL15 was identical to the apoprotein in derepressed cells of the nifB- mutant of K. pneumoniae (UN106) in its electrophoretic properties on nondenaturing polyacrylamide gels as well as in its ability to be activated by FeMoco. The constituent peptides migrated identically to those from purified MoFe protein during electrophoresis on denaturing gels. The concentrations of apoMoFe protein produced in nif-transformed strains of E. coli were greater than 50% of the levels of MoFe protein observed in derepressed wild-type K. pneumoniae. Systematic deletion of individual nif genes carried by pGH1 has established the requirements for the maximal production of the FeMoco-reactivatable apoMoFe protein to be the following gene products, NifHDKTYUSWZM+A. It appears that several of the genes (nifT, Y, U, W, and Z) are only required for maximal production of the apoMoFe protein, while others (nifH, D, K, and S) are absolutely required for synthesis of this protein in E. coli. One curious result is that the nifH gene product, the peptide of the Fe protein, but not active Fe protein itself, is required for formation of the apoMoFe protein. This suggests the possibility of a ternary complex of the NifH, D, and K peptides as the substrate for the processing to form the apoMoFe protein. We also find that nifM, the gene which processes the nifH protein into Fe protein (Howard, K.S., McLean, P.A., Hansen, F. B., Lemley, P.V., Kobla, K.S. & Orme-Johnson, W.H. (1986) J. Biol. Chem. 261, 772-778) can, under certain circumstances, partially replace other processing genes (i.e. nifTYU and/or WZ) although it is not essential for apoMoFe protein formation. It also appears that nifS and nifU, reported to play a role in Fe protein production in Azotobacter vinelandii, play no such role in K. pneumoniae, although these genes are involved in apoMoFe formation.(ABSTRACT TRUNCATED AT 400 WORDS)
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIron EXAFS of the iron-molybdenum cofactor of nitrogenaseMark R. Antonio, Boon Keng Teo, W. H. Orme-Johnson, Mark J. Nelson, Susan E. Groh, Paul A. Lindahl, Susan M. Kauzlarich, and Bruce A. AverillCite this: J. Am. Chem. Soc. 1982, 104, 17, 4703–4705Publication Date (Print):August 1, 1982Publication History Published online1 May 2002Published inissue 1 August 1982https://doi.org/10.1021/ja00381a045RIGHTS & PERMISSIONSArticle Views162Altmetric-Citations47LEARN 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 InReddit PDF (385 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
The X-ray structure of the nitrogenase MoFe protein has established the organization and architecture of its multimetallic cofactors, the P-cluster (Fe8S7-8) and the FeMo-cofactor (MoFe7S9:homocitrate). Nonetheless, until recently it has not been possible to detect or characterize a substrate or inhibitor interacting with the functioning enzyme. In the present study we have used 57Fe ENDOR to study the CO-inhibited turnover states of a novel suite of 56,57Fe isotopomers of the MoFe protein, including those in which these two clusters are selectively, as well as uniformly, labeled. CO-inhibited MoFe protein exhibits two distinct EPR signals, one under low and another under high CO pressure. The 57Fe measurements, along with an earlier 13C ENDOR study of bound 13CO (Pollock, R. C.; Lee, H. I.; Cameron, L. M.; DeRose, V. J.; Hales, B. J.; Orme-Johnson, W. H.; Hoffman, B. M. J. Am. Chem. Soc. 1995, 117, 8686−8687), show that the two EPR signals arise from CO-bound FeMo-cofactor, in one case with one bound CO and in the other with two bound CO, and they further provide initial insights into the properties of the inhibitor-bound cluster.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMechanistic studies of the coenzyme F420-reducing formate dehydrogenase from Methanobacterium formicicumNeil L. Schauer, James G. Ferry, John F. Honek, William H. Orme-Johnson, and Christopher WalshCite this: Biochemistry 1986, 25, 22, 7163–7168Publication Date (Print):November 4, 1986Publication History Published online1 May 2002Published inissue 4 November 1986https://pubs.acs.org/doi/10.1021/bi00370a059https://doi.org/10.1021/bi00370a059research-articleACS PublicationsRequest reuse permissionsArticle Views201Altmetric-Citations25LEARN 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
