Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism.

Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism. Research Abstract Details 

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Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism. Abstract Text:

Xiangshi Tan,Ivan V Surovtsev,Paul A Lindahl,

Acetyl-CoA synthase/carbon monoxide dehydrogenase is a Ni-Fe-S-containing enzyme that catalyzes the synthesis of acetyl-CoA from CO, CoA, and a methyl group. The methyl group is transferred onto the enzyme from a corrinoid-iron-sulfur protein (CoFeSP). The kinetics of two steps within the catalytic mechanism were studied using the stopped-flow method, including the insertion of CO into a putative Ni(2+)-CH(3) bond and the transfer of the resulting acetyl group to CoA. Neither step had been studied previously. Reactions were monitored indirectly, starting with the methylated intermediate form of the enzyme. Resulting traces were analyzed by constructing a simple kinetic model describing the catalytic mechanism under reducing conditions. Besides methyl group transfer, CO insertion, and acetyl group transfer, fitting to experimental traces required the inclusion of an inhibitory step in which CO reversibly bound to the form of the enzyme obtained immediately after product release. Global simulation of the reported datasets afforded a consistent set of kinetic parameters. The equilibrium constant for the overall synthesis of acetyl-CoA was estimated and compared to the product of the individual equilibrium constants. Simulations obtained with the model duplicated the essential behavior of the enzyme, in terms of the variation of activity with [CO], and the time-dependent decay of the NiFeC EPR signal upon reaction with CoFeSP. Under standard assay conditions, the model suggests that the vast majority of active enzyme molecules in a population should be in the methylated form, suggesting that the subsequent catalytic step, namely CO insertion, is rate limiting. This conclusion is further supported by a sensitivity analysis showing that the rate is most sensitively affected by a change in the rate coefficient associated with the CO insertion step.

Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism. Publishing Authors By Initials

X Tan,IV Surovtsev,PA Lindahl,

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Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism. Journal Published:

PUBLICATION TYPE: Research Support, Non-U.S. Gov

Journal: Journal of the American Chemical Society

VOLUME: 128

Page Numbers: 12331-8

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ISSN: 0002-7863

DAY: 20

MONTH: Sep

YEAR: 2006

Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism. Information

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LANGUAGE: eng

NlmUniqueID: 7503056

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Grant and Affiliation Information for Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism.

AFFILIATION: Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.

Country: United States

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MEDLINETA: J Am Chem Soc

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