Lu sandbox 1: Difference between revisions
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Pyruvate + TPP ==> Hydroxyethyl-TPP + CO2 | Pyruvate + TPP ==> Hydroxyethyl-TPP + CO2 | ||
The enzyme requires <scene name='Kenny_Coggins_Sandbox_1/Thdp/5'>TPP and Mg</scene>2+ as cofactors for catalysis. [[Image:Thiamine pyrophosphate.png|thumb|left|alt=Thiamine pyrophosphate.|Thiamine pyrophosphate (TPP) E1 cofactor.]] In this reaction, the ylide form of TPP attacks the electrophilic carbonyl group of pyruvate. This reflects the ability of TPP’s thiazolium ring, which primarily interacts with <scene name='Kenny_Coggins_Sandbox_1/Ile569_asp521/5'>Ile569 and Asp521</scene>, to add to carbonyl groups. Decarboxylation of the resulting alkoxide yields an enol complex. This enol resonates to form the ylide form of hydroxyethyl-TPP<ref name="book">Voet, D., Voet, J.G., and Pratt, C.W. (2008). Fundamentals of biochemistry. Hoboken, NJ: John Wiley and Sons, Inc.</ref>. During this reaction, the catalytic Mg2+ ion coordinates octahedrally with three protein ligands: <scene name='Kenny_Coggins_Sandbox_1/Asp230_and_asn260/2'>Asp230 and Asn 260</scene>, which bind TPP, and <scene name='Kenny_Coggins_Sandbox_1/Glu262/2'>Glu262</scene><ref name="PMID" />. [[Image:PyruvateDehydrgenaseMech1. | The enzyme requires <scene name='Kenny_Coggins_Sandbox_1/Thdp/5'>TPP and Mg</scene>2+ as cofactors for catalysis. [[Image:Thiamine pyrophosphate.png|thumb|left|alt=Thiamine pyrophosphate.|Thiamine pyrophosphate (TPP) E1 cofactor.]] In this reaction, the ylide form of TPP attacks the electrophilic carbonyl group of pyruvate. This reflects the ability of TPP’s thiazolium ring, which primarily interacts with <scene name='Kenny_Coggins_Sandbox_1/Ile569_asp521/5'>Ile569 and Asp521</scene>, to add to carbonyl groups. Decarboxylation of the resulting alkoxide yields an enol complex. This enol resonates to form the ylide form of hydroxyethyl-TPP<ref name="book">Voet, D., Voet, J.G., and Pratt, C.W. (2008). Fundamentals of biochemistry. Hoboken, NJ: John Wiley and Sons, Inc.</ref>. During this reaction, the catalytic Mg2+ ion coordinates octahedrally with three protein ligands: <scene name='Kenny_Coggins_Sandbox_1/Asp230_and_asn260/2'>Asp230 and Asn 260</scene>, which bind TPP, and <scene name='Kenny_Coggins_Sandbox_1/Glu262/2'>Glu262</scene><ref name="PMID" />. [[Image:PyruvateDehydrgenaseMech1.gif]] | ||
The second E1-catalyzed reaction is the transfer of the hydroxyethyl group to the lipoamide group of the next enzyme, dihydrolipoyltransacetylase (E2). The E2 lipoamide group consisting of lipoic acid linked to the amide group of a Lys residue. Lipoic acid contains a reactive cyclic disulfide that is reversibly reduced to give dihydrolipoamide. The ylide form of the hydroxyethyl group of the hydroxyethyl-TPP complex attacks this disulfide bond. TPP is then eliminated as it detaches with E1 and subsequently binds to the next pyruvate molecule<ref name="book" />. | The second E1-catalyzed reaction is the transfer of the hydroxyethyl group to the lipoamide group of the next enzyme, dihydrolipoyltransacetylase (E2). The E2 lipoamide group consisting of lipoic acid linked to the amide group of a Lys residue. Lipoic acid contains a reactive cyclic disulfide that is reversibly reduced to give dihydrolipoamide. The ylide form of the hydroxyethyl group of the hydroxyethyl-TPP complex attacks this disulfide bond. TPP is then eliminated as it detaches with E1 and subsequently binds to the next pyruvate molecule<ref name="book" />. | ||