Probing nitrogen-sensitive steps in the free-radical-mediated deamination of amino alcohols by ethanolamine ammonia-lyase

Russell R. Poyner, Mark A. Anderson, Vahe Bandarian, W. Wallace Cleland, George H. Reed

Research output: Contribution to journalArticle

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Abstract

The contribution of C-N bond-breaking/making steps to the rate of the free-radical-mediated deamination of vicinal amino alcohols by adenosylcobalamin-dependent ethanolamine ammonia-lyase has been investigated by 15N isotope effects (IE's) and by electron paramagnetic resonance (EPR) spectroscopy. 15N IE's were determined for three substrates, ethanolamine, (R)-2-aminopropanol, and (S)-2-aminopropanol, using isotope ratio mass spectrometry analysis of the product ammonia. Measurements with all three substrates gave measurable, normal 15N IE's; however, the IE of (S)-2-aminopropanol was ∼5-fold greater than that of the other two. Reaction mixtures frozen during the steady state show that the 2-aminopropanols give EPR spectra characteristic of the initial substrate radical, whereas ethanolamine gives spectra consistent with a product-related radical (Warncke, K.; Schmidt, J. C.; Kee, S.-C. J. Am. Chem. Soc. 1999, 121, 10522-10528). The steady-state concentration of the radical with (R)-2-aminopropanol is about half that observed with the S isomer, and with (R)-2-aminopropanol, the steady-state level of the radical is further reduced upon deuteration at C1. The results show that relative heights of kinetic barriers differ among the three substrates such that levels or identities of steady-state intermediates differ. 15N-sensitive steps are significant contributors to V/K with (S)-2-aminopropanol.

Original languageEnglish (US)
Pages (from-to)7120-7121
Number of pages2
JournalJournal of the American Chemical Society
Volume128
Issue number22
DOIs
StatePublished - Jun 7 2006

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Ethanolamine Ammonia-Lyase
Amino alcohols
Amino Alcohols
Ethanolamines
Deamination
Free radicals
Free Radicals
Isotopes
Ammonia
Nitrogen
Substrates
Paramagnetic resonance
Ethanolamine
Electron Spin Resonance Spectroscopy
Isomers
Mass spectrometry
2-aminopropanol
Spectroscopy
Kinetics
Mass Spectrometry

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Probing nitrogen-sensitive steps in the free-radical-mediated deamination of amino alcohols by ethanolamine ammonia-lyase. / Poyner, Russell R.; Anderson, Mark A.; Bandarian, Vahe; Cleland, W. Wallace; Reed, George H.

In: Journal of the American Chemical Society, Vol. 128, No. 22, 07.06.2006, p. 7120-7121.

Research output: Contribution to journalArticle

Poyner, Russell R. ; Anderson, Mark A. ; Bandarian, Vahe ; Cleland, W. Wallace ; Reed, George H. / Probing nitrogen-sensitive steps in the free-radical-mediated deamination of amino alcohols by ethanolamine ammonia-lyase. In: Journal of the American Chemical Society. 2006 ; Vol. 128, No. 22. pp. 7120-7121.
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abstract = "The contribution of C-N bond-breaking/making steps to the rate of the free-radical-mediated deamination of vicinal amino alcohols by adenosylcobalamin-dependent ethanolamine ammonia-lyase has been investigated by 15N isotope effects (IE's) and by electron paramagnetic resonance (EPR) spectroscopy. 15N IE's were determined for three substrates, ethanolamine, (R)-2-aminopropanol, and (S)-2-aminopropanol, using isotope ratio mass spectrometry analysis of the product ammonia. Measurements with all three substrates gave measurable, normal 15N IE's; however, the IE of (S)-2-aminopropanol was ∼5-fold greater than that of the other two. Reaction mixtures frozen during the steady state show that the 2-aminopropanols give EPR spectra characteristic of the initial substrate radical, whereas ethanolamine gives spectra consistent with a product-related radical (Warncke, K.; Schmidt, J. C.; Kee, S.-C. J. Am. Chem. Soc. 1999, 121, 10522-10528). The steady-state concentration of the radical with (R)-2-aminopropanol is about half that observed with the S isomer, and with (R)-2-aminopropanol, the steady-state level of the radical is further reduced upon deuteration at C1. The results show that relative heights of kinetic barriers differ among the three substrates such that levels or identities of steady-state intermediates differ. 15N-sensitive steps are significant contributors to V/K with (S)-2-aminopropanol.",
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