The Mechanism of Action of Ethanolamine Ammonia-Lyase, a B12-dependent Enzyme

Babior, Bernard M.; Moss, Thomas H.; Orme‐Johnson, William H.; Beinert, Helmut

doi:10.1016/s0021-9258(19)42452-6

Cited by 113 publications

(93 citation statements)

References 21 publications

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“…The attenuation of the dipolar interaction by rapid rotation of the organic radical as described above seems unlikely because those enzymes which act on large substrates exhibit EPR spectra essentially identical to those which have smaller substrates. Indeed, any free rotation model would seem to be excluded by the observations [2,5] that the EPR spectra are unchanged at temperatures near liquid helium where thermally induced motion would be greatly reduced.…”

Section: Discussionmentioning

confidence: 99%

“…8 and Valinsky, J.E., Fee, J.A. and Abeles, R.H., unpublished)and ethanolamine ammonia lyase [5] it has been shown that some spin density exists on certain atoms of the respective substrates.…”

Section: Introductionmentioning

confidence: 91%

“…A, diol dehydrase plus ethylene glycol (Valinsky, J.E., Fee, J.A. and Abeles, R.H., unpublished); B, ethanolamine ammonia lyase plus L-2-aminopropanol[5]; C, diol dehydrase plus propane diol[3]; D, glycerol dehydrase plus propane diol; E, ribonucleotide reductase plus adenosine triphosphate[ 1]. Spectra were taken from the various references and were standardized photographically along the magnetic field.…”

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confidence: 99%

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A physical explanation of the EPR spectrum observed during catalysis by enzymes utilizing coenzyme B

Schepler

Dunham

Sands

et al. 1975

Biochimica et Biophysica Acta (BBA) - Enzymology

100

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We have proposed that the "doublet" EPR spectra observed during catalysis by a number of coenzyme B12-requiring enzymes arises from a weak electrostatic exchange interaction between an organic free radical and low spin Co(II), B12r. By varying the magnitude of the exchange of coupling we have quite accurately simulated the published EPR spectra from the enzyme systems: diol dehydrase, glycerol dehydrase, ribonucleotide reductase, and ethanolamine ammon-ia lyase. A dipolar model was shown to be incompatible with the observed properties of these systems.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 91%

mentioning

confidence: 99%

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A physical explanation of the EPR spectrum observed during catalysis by enzymes utilizing coenzyme B

Schepler

Dunham

Sands

et al. 1975

Biochimica et Biophysica Acta (BBA) - Enzymology

100

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“…However, accurate data for the rate of AdoCbl homolysis on enzymes are lacking. A related question is how homolysis is coupled to hydrogen abstraction from the substrate, since for all the enzymes examined, cleavage of the coenzyme depends on the substrate being bound (12)(13)(14)(15). Furthermore, despite its central role in the mechanism of these enzymes, adenosyl radical itself has never been observed, for example by electron paramagnetic resonance (EPR), as an intermediate.…”

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confidence: 99%

Coupling of Cobalt−Carbon Bond Homolysis and Hydrogen Atom Abstraction in Adenosylcobalamin-Dependent Glutamate Mutase

1998

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Adenosylcobalamin-dependent glutamate mutase catalyzes an unusual carbon skeleton rearrangement that proceeds through the formation of free radical intermediates generated by the substrate-induced cleavage of the coenzyme cobalt-carbon bond. The reaction was studied at 10 degrees C with various concentrations of L-glutamate and L-threo-3-methylaspartate and with use of stopped-flow spectroscopy to follow the formation of cob(II)alamin. Either substrate induces rapid formation of cob(II)alamin, which accumulates to account for about 25% of the total enzyme species in the steady state when substrate is saturating. Measurements of the rate constant for the formation of cob(II)alamin demonstrate that the enzyme accelerates the rate of homolysis of the cobalt-carbon bond by at least 10(12)-fold. Very large isotope effects on cob(II)alamin formation, of 28 and 35, are observed with deuterated L-glutamate and deuterated L-threo-3-methylaspartate, respectively. This implies a mechanism in which Co-C bond homolysis is kinetically coupled to substrate hydrogen abstraction. Therefore, adenosyl radical can only be formed as a high-energy intermediate only at very low concentrations on the enzyme. The magnitude of the isotope effects suggests that hydrogen tunneling may play an important role catalysis.

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“…18 ) wurde hei 4°C auf etwa 10 ml eingeengt und mit einer Quecksilber-Hochdrucklampe 24 Stunden hestrah.lt. Szintillisa$ionsmessungen ergaben, daß in den Vesikeln 0, 55…”

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Synthese Von Kobalt- Rhodium- Eisen- Und Rutheniumkomplexen Mit Cholestan-23-Dioxim. Ihre Charakterisierung Und Anwendung Als Modelle Fur Biokatalysatoren

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methylester Jj> als Alkylierungsmittel und mit Pyridin als axialem Liganden " 35 5.7. Synthese der alkylierten C-markierten Kobaltkomplexe 26a, 26b, 26c aus Brommethyl-^C-methylmalonsäure-di-naphthylmathylester J_6 als Alkylierungsmittel und mit Pyridin als axialem liganden...37 5.8. Synthese des alkylierten Kobaltkomplexes 28 aus Cholesteryl-^bromid 27 als Alkylierungscaittel und mit Pyridin als axialem Liganden ..

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The Mechanism of Action of Ethanolamine Ammonia-Lyase, a B12-dependent Enzyme

Cited by 113 publications

References 21 publications

A physical explanation of the EPR spectrum observed during catalysis by enzymes utilizing coenzyme B

A physical explanation of the EPR spectrum observed during catalysis by enzymes utilizing coenzyme B

Coupling of Cobalt−Carbon Bond Homolysis and Hydrogen Atom Abstraction in Adenosylcobalamin-Dependent Glutamate Mutase

Synthese Von Kobalt- Rhodium- Eisen- Und Rutheniumkomplexen Mit Cholestan-23-Dioxim. Ihre Charakterisierung Und Anwendung Als Modelle Fur Biokatalysatoren

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