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Arrange the steps in the reaction catalyzed by threonine dehydrates in order, using the racemization reaction shown in part B as a guide. Note that the threonine dehydrates reaction is not a racemization, but instead features an elimination at the ß carbon of threonine.

Arrange the steps in the reaction catalyzed by threonine dehydrates in order, using the racemization reaction shown in part B as a guide. Note that the threonine dehydrates reaction is not a racemization, but instead features an elimination at the ß carbon of threonine.

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
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O Macmillan Learning Threonine can be broken down by the enzyme threonine dehydratase, which catalyzes the conversion of threonine to a-ketobutyrate and ammonia as shown in part A of the figure. The enzyme uses PLP as a cofactor. The general mechanism of PLP-dependent racemization is shown in part B of the figure. A B R- -C COO- H L-Amino acid Enz + NH3 Lys + H ‚N+ НО. H₂C CH H CH3- 11- OH CH-CH -B R НО. NH3 H₂C +NH -|| COO COO PLP Threonine dehydratase 1~ H+ HO H₂C² R с || +NH CH CH₂ CH₂ COO 1/m Quinonoid intermediate a-Ketobutyrate HO R H-C-COO- H₂C COO + NH, + H,O +NH || CH Lys-NH₂ Enz R H-C +NH₂ 3 COO- D-Amino acid Pyridoxal phosphate (internal aldimine form, on regenerated enzyme) Arrange the steps in the reaction catalyzed by threonine dehydrates in order, using the racemization reaction shown in part B as a guide. Note that the threonine dehydrates reaction is not a racemization, but instead features an elimination at the ß carbon of threonine.
Transcribed Image Text:O Macmillan Learning Threonine can be broken down by the enzyme threonine dehydratase, which catalyzes the conversion of threonine to a-ketobutyrate and ammonia as shown in part A of the figure. The enzyme uses PLP as a cofactor. The general mechanism of PLP-dependent racemization is shown in part B of the figure. A B R- -C COO- H L-Amino acid Enz + NH3 Lys + H ‚N+ НО. H₂C CH H CH3- 11- OH CH-CH -B R НО. NH3 H₂C +NH -|| COO COO PLP Threonine dehydratase 1~ H+ HO H₂C² R с || +NH CH CH₂ CH₂ COO 1/m Quinonoid intermediate a-Ketobutyrate HO R H-C-COO- H₂C COO + NH, + H,O +NH || CH Lys-NH₂ Enz R H-C +NH₂ 3 COO- D-Amino acid Pyridoxal phosphate (internal aldimine form, on regenerated enzyme) Arrange the steps in the reaction catalyzed by threonine dehydrates in order, using the racemization reaction shown in part B as a guide. Note that the threonine dehydrates reaction is not a racemization, but instead features an elimination at the ß carbon of threonine.
Macmillan Learning Arrange the steps in the reaction catalyzed by threonine dehydrates in order, using the racemization reaction shown in part B as a guide. Note that the threonine dehydrates reaction is not a racemization, but instead features an elimination at the ß carbon of threonine. First event Final event Answer Bank Threonine forms an aldimine bond with PLP, displacing lysine. Reversal of the link to PLP releases dehydrated threonine from PLP Proton abstraction at an a carbon leads to ß elimination of —OH. Hydrolysis of dehydrated threonine releases ammonia. Rearrangement of an enamine forms an imine.
Transcribed Image Text:Macmillan Learning Arrange the steps in the reaction catalyzed by threonine dehydrates in order, using the racemization reaction shown in part B as a guide. Note that the threonine dehydrates reaction is not a racemization, but instead features an elimination at the ß carbon of threonine. First event Final event Answer Bank Threonine forms an aldimine bond with PLP, displacing lysine. Reversal of the link to PLP releases dehydrated threonine from PLP Proton abstraction at an a carbon leads to ß elimination of —OH. Hydrolysis of dehydrated threonine releases ammonia. Rearrangement of an enamine forms an imine.
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