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Synthesis and binding properties of linked azamacrocycles
322
Abstracts
SYNTHESIS AND BINDING PROPERTIES OF LINKED AZAMACROCYCLES. LO42John w ‘ebert and Jonathan L. Sessler, Department of Chemistry, University
of Texas,
Austin,
Texas
78712
USA.
Saturated azamacrocycles, in particular triazacyclononanes, have been shown to stabilize a variety of binuclear species. The synthesis and physical properties of a series of novel hydrocarbon-linked, saturmacrocycles and their use as binucleating ated, nitrogen-containing ligands will be presented. The most elaborate of this series is designed to provide a vacant coordination site at one metal center while maintaining full coordination at the other metal center. These ligands are potentially suitable for modelling the active sites of bimetallic proteins, such as hemerythrin.
LO43
X-RAY ABSORPTION SPECTROSCOPY OF PROTEIN A OF METHANE MONOOXYGENASE. (1) Jane Dewitt, Britt Hedman, Keith 0. Hodgson.
(2) James Bentsen, Stephen J. Lippard. (3) Jeffrey Green, Simon Tilkington, Howard Dalton. (1) Department of Chemistry and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA. (2) Department of Chemistry, Massachussetts Institute of Technology, Cambridge, MA 02139, USA. (3) Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, England. The Fe K edge and EXAFS data for the initially oxidized form of Protein A of methane monooxygenase (MMO) from Methylococcus cupsulatus (Bath) and Methylosinus trichosporium (OB3b), and of the reduced form of Protein A of MM0 from Methylococcus cupsulutus (Bath) have been measured. The effect of photoreduction of the oxidized protein samples to the semimet state by the x-ray beam on the Fe K edge, as well as detailed results of fits to the EXAFS data for the semimet (binuclear iron center with an Fe-Fe distance of - 3.4 A) and reduced protein samples will be presented.
LO44
SPECTROSCOPICSTUDIES OF THE METHANE MONOOKYGENASE FROM Methylosinus trichosporium OB3b. B& EQ& J.D. LIPSCOMB. K.K. SURERUS, M.P. HENDRICH. E. MUNCK. Dept. of Biochemistry, Univ. of Minnesota, Minneapolis, MN, 55455 USA. The soluble methane monooxygenase from M. tichosporium has been puritied in high yield with specific activity 8 to 25 times higher than previously reported. Mossbauer studies of the oxidized, ?eenriched hydroxylase component show an ant$erromagnetically coupled (S=O)iron cluster with a 1:1 ratio of non-identical Fe(II1) sites at pH 9.3. In contrast, these sites were not resolved at pH 7.0, where the enzyme is most active. Partial reduction yields an EPR active species exhibiting all resonances below g=2 Q av~1.85), and EPR power saturationmeasurements indicate antjferromagnetic coupling with -2J=58 cm-i. Mossbauer spectra of the fully red& cluster show all iron is high spin ferrous (S=2). An EPR signal characteristic of an integer spin system is observed at g=15. Simulations suggest this EPR signal results fromferromagnetic coupling of two Fe(H) (S=4). These observations are all consistent with the presence of a u-0x0 or a u-hydroxo bridged binuclear iron cluster. Quantitation of cluster iron by these spectroscopic methods shows the increased specific activity is associated with an increased concentration of binuclear cluster, and suggests the most active hydroxylase may contain more than 1 binuclear cluster.
Abstracts
SYNTHESIS AND BINDING PROPERTIES OF LINKED AZAMACROCYCLES. LO42John w ‘ebert and Jonathan L. Sessler, Department of Chemistry, University
of Texas,
Austin,
Texas
78712
USA.
Saturated azamacrocycles, in particular triazacyclononanes, have been shown to stabilize a variety of binuclear species. The synthesis and physical properties of a series of novel hydrocarbon-linked, saturmacrocycles and their use as binucleating ated, nitrogen-containing ligands will be presented. The most elaborate of this series is designed to provide a vacant coordination site at one metal center while maintaining full coordination at the other metal center. These ligands are potentially suitable for modelling the active sites of bimetallic proteins, such as hemerythrin.
LO43
X-RAY ABSORPTION SPECTROSCOPY OF PROTEIN A OF METHANE MONOOXYGENASE. (1) Jane Dewitt, Britt Hedman, Keith 0. Hodgson.
(2) James Bentsen, Stephen J. Lippard. (3) Jeffrey Green, Simon Tilkington, Howard Dalton. (1) Department of Chemistry and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA. (2) Department of Chemistry, Massachussetts Institute of Technology, Cambridge, MA 02139, USA. (3) Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, England. The Fe K edge and EXAFS data for the initially oxidized form of Protein A of methane monooxygenase (MMO) from Methylococcus cupsulatus (Bath) and Methylosinus trichosporium (OB3b), and of the reduced form of Protein A of MM0 from Methylococcus cupsulutus (Bath) have been measured. The effect of photoreduction of the oxidized protein samples to the semimet state by the x-ray beam on the Fe K edge, as well as detailed results of fits to the EXAFS data for the semimet (binuclear iron center with an Fe-Fe distance of - 3.4 A) and reduced protein samples will be presented.
LO44
SPECTROSCOPICSTUDIES OF THE METHANE MONOOKYGENASE FROM Methylosinus trichosporium OB3b. B& EQ& J.D. LIPSCOMB. K.K. SURERUS, M.P. HENDRICH. E. MUNCK. Dept. of Biochemistry, Univ. of Minnesota, Minneapolis, MN, 55455 USA. The soluble methane monooxygenase from M. tichosporium has been puritied in high yield with specific activity 8 to 25 times higher than previously reported. Mossbauer studies of the oxidized, ?eenriched hydroxylase component show an ant$erromagnetically coupled (S=O)iron cluster with a 1:1 ratio of non-identical Fe(II1) sites at pH 9.3. In contrast, these sites were not resolved at pH 7.0, where the enzyme is most active. Partial reduction yields an EPR active species exhibiting all resonances below g=2 Q av~1.85), and EPR power saturationmeasurements indicate antjferromagnetic coupling with -2J=58 cm-i. Mossbauer spectra of the fully red& cluster show all iron is high spin ferrous (S=2). An EPR signal characteristic of an integer spin system is observed at g=15. Simulations suggest this EPR signal results fromferromagnetic coupling of two Fe(H) (S=4). These observations are all consistent with the presence of a u-0x0 or a u-hydroxo bridged binuclear iron cluster. Quantitation of cluster iron by these spectroscopic methods shows the increased specific activity is associated with an increased concentration of binuclear cluster, and suggests the most active hydroxylase may contain more than 1 binuclear cluster.