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The enzyme cytidine deaminase catalyzes the conversion of cytidine to uridine. Cytidine deaminase catalyzes the reaction through an addition of water across the cytidine 3,4-bond, forming a tetrahedral intermediate followed by the elimination of NH3 to form the product uridine. This is like the addition-elimination mechanism that we studied for adenosine deaminase. Cytidine deaminase HO. NH₂ OH OH cytosine N I R N + H₂O cytidine ΝΗ uridine The Km value for the substrate cytidine is 2.5 x 10-4 M, and the K₁ for competitive inhibition by the product uridine is 2.5 × 10-³ M. 4 HO. A reduced derivative of the product, 3,4,5,6-tetrahydrouridine was shown to be a fully reversible competitive inhibitor with a Ki of 2.4 x 10-7 M, a value approximately 10,000 times lower than that of the product uridine. NH₂ 3NH R= D-ribose R uracil ring numbering N HOH OH uridine ΝΗ H HH OH H- H N R + NH3 .H 'N' 3,4,5,6-tetra- hydrouridine a.) Draw a structure of the intermediate that we predict to form during the conversion of cytidine to uridine. b.) Use a mechanistic argument to explain the high inhibitor potency of 3,4,5,6- tetrahydrouridine.

The enzyme cytidine deaminase catalyzes the conversion of cytidine to uridine. Cytidine deaminase catalyzes the reaction through an addition of water across the cytidine 3,4-bond, forming a tetrahedral intermediate followed by the elimination of NH3 to form the product uridine. This is like the addition-elimination mechanism that we studied for adenosine deaminase. Cytidine deaminase HO. NH₂ OH OH cytosine N I R N + H₂O cytidine ΝΗ uridine The Km value for the substrate cytidine is 2.5 x 10-4 M, and the K₁ for competitive inhibition by the product uridine is 2.5 × 10-³ M. 4 HO. A reduced derivative of the product, 3,4,5,6-tetrahydrouridine was shown to be a fully reversible competitive inhibitor with a Ki of 2.4 x 10-7 M, a value approximately 10,000 times lower than that of the product uridine. NH₂ 3NH R= D-ribose R uracil ring numbering N HOH OH uridine ΝΗ H HH OH H- H N R + NH3 .H 'N' 3,4,5,6-tetra- hydrouridine a.) Draw a structure of the intermediate that we predict to form during the conversion of cytidine to uridine. b.) Use a mechanistic argument to explain the high inhibitor potency of 3,4,5,6- tetrahydrouridine.

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
Problem 1P
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The enzyme cytidine deaminase catalyzes the conversion of cytidine to uridine. Cytidine deaminase catalyzes the reaction through an addition of water across the cytidine 3,4-bond, forming a tetrahedral intermediate followed by the elimination of NH3 to form the product uridine. This is like the addition-elimination mechanism that we studied for adenosine deaminase. Cytidine deaminase НО. NH₂ N пOH OH cytosine R + H₂O cytidine The Km value for the substrate cytidine is 2.5 × 10-4 M, and the K; for competitive inhibition by the product uridine is 2.5 × 10-³ M. N R A reduced derivative of the product, 3,4,5,6-tetrahydrouridine was shown to be a fully reversible competitive inhibitor with a Ki of 2.4 x 10-7 M, a value approximately 10,000 times lower than that of the product uridine. NH₂ NH uridine HO. N R R = D-ribose HOH OH uridine 3NH uracil ring numbering H NH H H + NH3 H OH H 3,4,5,6-tetra- hydrouridine a.) Draw a structure of the intermediate that we predict to form during the conversion of cytidine to uridine. b.) Use a mechanistic argument to explain the high inhibitor potency of 3,4,5,6- tetrahydrouridine.
Transcribed Image Text:The enzyme cytidine deaminase catalyzes the conversion of cytidine to uridine. Cytidine deaminase catalyzes the reaction through an addition of water across the cytidine 3,4-bond, forming a tetrahedral intermediate followed by the elimination of NH3 to form the product uridine. This is like the addition-elimination mechanism that we studied for adenosine deaminase. Cytidine deaminase НО. NH₂ N пOH OH cytosine R + H₂O cytidine The Km value for the substrate cytidine is 2.5 × 10-4 M, and the K; for competitive inhibition by the product uridine is 2.5 × 10-³ M. N R A reduced derivative of the product, 3,4,5,6-tetrahydrouridine was shown to be a fully reversible competitive inhibitor with a Ki of 2.4 x 10-7 M, a value approximately 10,000 times lower than that of the product uridine. NH₂ NH uridine HO. N R R = D-ribose HOH OH uridine 3NH uracil ring numbering H NH H H + NH3 H OH H 3,4,5,6-tetra- hydrouridine a.) Draw a structure of the intermediate that we predict to form during the conversion of cytidine to uridine. b.) Use a mechanistic argument to explain the high inhibitor potency of 3,4,5,6- tetrahydrouridine.
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