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3. Enzyme specificity. To determine the specificity of substrate binding for a particular enzyme/protein, structurally related compounds may be used as potential substrates and Km values may be calculated. However, many compounds structurally related to the substrate may bind to the active site but cannot be converted to product. In these instances, the substrate analogs are used as potential competitive inhibitors of substrate binding. Low K, values indicate high affinity of the enzyme for the inhibitor, whereas high K,values indicate low binding affinity. Consider the enzyme xanthine oxidase, which catalyzes the formation of uric acid from the purine bases hypoxanthine or xanthine in humans. The Km for hypoxanthine is 15.0 μM and for xanthine it is 45.0 μM. A few compounds used as competitive inhibitors of the normal substrate hypoxanthine are listed in the table below with their K, values. Comparing the structures of hypoxanthine with the listed substrate analogs, what can you conclude about the characteristics of molecules that this enzyme binds at its active site? OH hypoxanthine (Km = 15.0 μm) OH xanthine oxidase xanthine (Km = 45.0 μm) xanthine oxidase OH HO HO OH uric acid N- OH OH N OH uric acid Substrate analog Purine Adenine Guanine Allopurinol Inosine HO. HOH Structure 7N- N1 NH₂ OH OH OH "NH₂ K, (UM) 900 800 300 38 900

3. Enzyme specificity. To determine the specificity of substrate binding for a particular enzyme/protein, structurally related compounds may be used as potential substrates and Km values may be calculated. However, many compounds structurally related to the substrate may bind to the active site but cannot be converted to product. In these instances, the substrate analogs are used as potential competitive inhibitors of substrate binding. Low K, values indicate high affinity of the enzyme for the inhibitor, whereas high K,values indicate low binding affinity. Consider the enzyme xanthine oxidase, which catalyzes the formation of uric acid from the purine bases hypoxanthine or xanthine in humans. The Km for hypoxanthine is 15.0 μM and for xanthine it is 45.0 μM. A few compounds used as competitive inhibitors of the normal substrate hypoxanthine are listed in the table below with their K, values. Comparing the structures of hypoxanthine with the listed substrate analogs, what can you conclude about the characteristics of molecules that this enzyme binds at its active site? OH hypoxanthine (Km = 15.0 μm) OH xanthine oxidase xanthine (Km = 45.0 μm) xanthine oxidase OH HO HO OH uric acid N- OH OH N OH uric acid Substrate analog Purine Adenine Guanine Allopurinol Inosine HO. HOH Structure 7N- N1 NH₂ OH OH OH "NH₂ K, (UM) 900 800 300 38 900

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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**Enzyme Specificity** To determine the specificity of substrate binding for a particular enzyme/protein, structurally related compounds may be used as potential substrates and \(K_m\) values may be calculated. However, many compounds structurally related to the substrate may bind to the active site but cannot be converted to product. In these instances, the substrate analogs are used as potential competitive inhibitors of substrate binding. Low \(K_i\) values indicate high affinity of the enzyme for the inhibitor, whereas high \(K_i\) values indicate low binding affinity. Consider the enzyme xanthine oxidase, which catalyzes the formation of uric acid from the purine bases hypoxanthine or xanthine in humans. The \(K_m\) for hypoxanthine is 15.0 µM and for xanthine it is 45.0 µM. A few compounds used as competitive inhibitors of the normal substrate hypoxanthine are listed in the table below with their \(K_i\) values. **Comparing the structures of hypoxanthine with the listed substrate analogs, what can you conclude about the characteristics of molecules that this enzyme binds at its active site?** **Table: Substrate Analogs** | Substrate Analog | Structure | \(K_i\) (µM) | |------------------|-----------|--------------| | Purine | ![Purine Structure](https://via.placeholder.com/40) | 900 | | Adenine | ![Adenine Structure](https://via.placeholder.com/40) | 800 | | Guanine | ![Guanine Structure](https://via.placeholder.com/40) | 300 | | Allopurinol | ![Allopurinol Structure](https://via.placeholder.com/40) | 38 | | Inosine | ![Inosine Structure](https://via.placeholder.com/40) | 900 | **Diagrams Description:** - **Reaction Pathway:** - Hypoxanthine is converted to uric acid via the enzyme xanthine oxidase. \(K_m = 15.0 \, \mu\text{M}\). - Xanthine is also converted to uric acid via xanthine oxidase. \(K_m = 45.0 \, \mu\text{M}\). **Observations:** - Allopurin
Transcribed Image Text:**Enzyme Specificity** To determine the specificity of substrate binding for a particular enzyme/protein, structurally related compounds may be used as potential substrates and \(K_m\) values may be calculated. However, many compounds structurally related to the substrate may bind to the active site but cannot be converted to product. In these instances, the substrate analogs are used as potential competitive inhibitors of substrate binding. Low \(K_i\) values indicate high affinity of the enzyme for the inhibitor, whereas high \(K_i\) values indicate low binding affinity. Consider the enzyme xanthine oxidase, which catalyzes the formation of uric acid from the purine bases hypoxanthine or xanthine in humans. The \(K_m\) for hypoxanthine is 15.0 µM and for xanthine it is 45.0 µM. A few compounds used as competitive inhibitors of the normal substrate hypoxanthine are listed in the table below with their \(K_i\) values. **Comparing the structures of hypoxanthine with the listed substrate analogs, what can you conclude about the characteristics of molecules that this enzyme binds at its active site?** **Table: Substrate Analogs** | Substrate Analog | Structure | \(K_i\) (µM) | |------------------|-----------|--------------| | Purine | ![Purine Structure](https://via.placeholder.com/40) | 900 | | Adenine | ![Adenine Structure](https://via.placeholder.com/40) | 800 | | Guanine | ![Guanine Structure](https://via.placeholder.com/40) | 300 | | Allopurinol | ![Allopurinol Structure](https://via.placeholder.com/40) | 38 | | Inosine | ![Inosine Structure](https://via.placeholder.com/40) | 900 | **Diagrams Description:** - **Reaction Pathway:** - Hypoxanthine is converted to uric acid via the enzyme xanthine oxidase. \(K_m = 15.0 \, \mu\text{M}\). - Xanthine is also converted to uric acid via xanthine oxidase. \(K_m = 45.0 \, \mu\text{M}\). **Observations:** - Allopurin
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