Time-resolved measurements of the photolysis and recombination of adenosylcobalamin bound to glutamate mutase.

Time-resolved measurements of the photolysis and recombination of adenosylcobalamin bound to glutamate mutase. Research Abstract Details 

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Time-resolved measurements of the photolysis and recombination of adenosylcobalamin bound to glutamate mutase. Abstract Text:

Roseanne J Sension,D Ahmasi Harris,Andrew Stickrath,Allwyn G Cole,Christel C Fox,E Neil G Marsh,

Femtosecond to nanosecond transient absorption spectroscopy is used to investigate the photolysis of 5'-deoxyadenosylcobalamin (coenzyme B12, AdoCbl) bound to glutamate mutase. The photochemistry of AdoCbl is found to be inherently dependent upon the environment of the cofactor. Excitation of AdoCbl bound to glutamate mutase results in formation of a metal-to-ligand charge transfer intermediate state which decays to form cob(II)alamin with a time constant of 105 ps. This observation is in contrast to earlier measurements in water where the photohomolysis proceeds through an intermediate state in which the axial dimethylbenzimidazole ligand appears to have dissociated, and measurements in ethylene glycol where prompt bond homolysis is observed (Yoder, L. M.; Cole, A. G.; Walker, L. A., II; Sension, R. J. J. Phys. Chem. B 2001, 105, 12180-12188). The quantum yield for formation of stable radical pairs in the enzyme is found to be phi = 0.05 +/- 0.03, and the resulting intrinsic rate constants for geminate recombination and "cage escape" are 1.0 +/- 0.1 and 0.05 +/- 0.03 ns(-1), respectively. The rate constant for geminate recombination is 30% less than that observed for AdoCbl in water or ethylene glycol. This reduction is insufficient to account for the 10(12)-fold increase in the homolysis rate observed when substrate is bound to the protein. Finally, the protein provides a cage to prevent diffusive loss of the adenosyl radical; however, the ultimate yield for long-lived radicals is determined by the evolution from a singlet to a triplet radical pair as proposed for AdoCbl in ethylene glycol.

Time-resolved measurements of the photolysis and recombination of adenosylcobalamin bound to glutamate mutase. Publishing Authors By Initials

RJ Sension,DA Harris,A Stickrath,AG Cole,CC Fox,EN Marsh,

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Time-resolved measurements of the photolysis and recombination of adenosylcobalamin bound to glutamate mutase. Journal Published:

PUBLICATION TYPE: Research Support, U.S. Gov't,

Journal: The journal of physical chemistry. B

VOLUME: 109

Page Numbers: 18146-52

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ISSN: 1520-6106

DAY: 29

MONTH: Sep

YEAR: 2005

Time-resolved measurements of the photolysis and recombination of adenosylcobalamin bound to glutamate mutase. Information

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LANGUAGE: eng

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Grant and Affiliation Information for Time-resolved measurements of the photolysis and recombination of adenosylcobalamin bound to glutamate mutase.

AFFILIATION: Departments of Chemistry and of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055, USA. rsension@umich.edu

Country: United States

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MEDLINETA: J Phys Chem B

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