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Questions and Answers
Which strategy involves a functional group on the protein either donating a proton or accepting a proton during the course of the reaction?
Which strategy involves a functional group on the protein either donating a proton or accepting a proton during the course of the reaction?
Which enzyme uses histidine 57 as a general base catalyst and later as a general acid catalyst in its reaction mechanism?
Which enzyme uses histidine 57 as a general base catalyst and later as a general acid catalyst in its reaction mechanism?
Which type of catalysis involves the use of a metal ion to facilitate the reaction?
Which type of catalysis involves the use of a metal ion to facilitate the reaction?
Which strategy involves the enzyme bringing the substrate and catalytic groups together in an orientation that facilitates the reaction?
Which strategy involves the enzyme bringing the substrate and catalytic groups together in an orientation that facilitates the reaction?
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Which type of coenzymes are usually synthesized from vitamins and participate in catalysis by providing functional groups?
Which type of coenzymes are usually synthesized from vitamins and participate in catalysis by providing functional groups?
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Which amino acid is unsuitable for general acid-base catalysis due to its inability to extract a proton at low pH?
Which amino acid is unsuitable for general acid-base catalysis due to its inability to extract a proton at low pH?
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What inhibits the absorption of thiamin and displaces pyridoxal phosphate from its protein-binding sites?
What inhibits the absorption of thiamin and displaces pyridoxal phosphate from its protein-binding sites?
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Which type of protease uses two aspartate residues for acid-base catalysis?
Which type of protease uses two aspartate residues for acid-base catalysis?
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Which type of protease can use histidine for catalysis?
Which type of protease can use histidine for catalysis?
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What do enzymes in amino acid metabolism use for catalysis?
What do enzymes in amino acid metabolism use for catalysis?
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What do almost all polar amino acids participate directly in during catalysis?
What do almost all polar amino acids participate directly in during catalysis?
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What results in the loss of specific enzyme activities that depend on the coenzyme form of the vitamin?
What results in the loss of specific enzyme activities that depend on the coenzyme form of the vitamin?
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What happens to coenzymes during the reaction?
What happens to coenzymes during the reaction?
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What is the primary source for the synthesis of coenzymes?
What is the primary source for the synthesis of coenzymes?
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What do activation-transfer coenzymes do to participate in catalysis?
What do activation-transfer coenzymes do to participate in catalysis?
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What type of coenzymes have almost no catalytic power when not bound to the enzyme?
What type of coenzymes have almost no catalytic power when not bound to the enzyme?
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Which amino acid is involved in stabilizing the oxyanion tetrahedral transition-state complex in enzyme catalysis?
Which amino acid is involved in stabilizing the oxyanion tetrahedral transition-state complex in enzyme catalysis?
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What type of catalysis involves the substrate being covalently linked to an amino acid side chain at the enzyme's active site during the reaction?
What type of catalysis involves the substrate being covalently linked to an amino acid side chain at the enzyme's active site during the reaction?
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What is the primary function of the catalytic triad consisting of aspartate, histidine, and serine in enzyme catalysis?
What is the primary function of the catalytic triad consisting of aspartate, histidine, and serine in enzyme catalysis?
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Which type of catalysis refers to the enzyme forcing substrates to bind in a manner that places reactive groups in the appropriate orientation for a reaction to occur?
Which type of catalysis refers to the enzyme forcing substrates to bind in a manner that places reactive groups in the appropriate orientation for a reaction to occur?
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What type of catalysis involves the activation of water by the active-site histidine for a nucleophilic attack?
What type of catalysis involves the activation of water by the active-site histidine for a nucleophilic attack?
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What is the role of metal ions in carbonic anhydrase catalysis?
What is the role of metal ions in carbonic anhydrase catalysis?
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What type of intermediates are present in the energy diagram of real enzymatic reactions?
What type of intermediates are present in the energy diagram of real enzymatic reactions?
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What is the primary function of the serine or cysteine residues in enzymes like chymotrypsin during catalysis?
What is the primary function of the serine or cysteine residues in enzymes like chymotrypsin during catalysis?
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What is the primary role of gastric acid in denaturing proteins in the stomach?
What is the primary role of gastric acid in denaturing proteins in the stomach?
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What type of coenzymes use catalysis by approximation to transfer a phosphate from a nucleoside triphosphate to a nucleoside monophosphate?
What type of coenzymes use catalysis by approximation to transfer a phosphate from a nucleoside triphosphate to a nucleoside monophosphate?
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What is the primary function of peptide backbone –NH groups in enzyme catalysis?
What is the primary function of peptide backbone –NH groups in enzyme catalysis?
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What is the primary role of dissociating products in enzyme-catalyzed reactions?
What is the primary role of dissociating products in enzyme-catalyzed reactions?
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What is the primary role of the hydroxyl group of a serine residue in chymotrypsin catalysis?
What is the primary role of the hydroxyl group of a serine residue in chymotrypsin catalysis?
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What is the role of the aspartate and histidine in the chymotrypsin catalytic mechanism?
What is the role of the aspartate and histidine in the chymotrypsin catalytic mechanism?
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What provides the scissile-bond specificity in the chymotrypsin catalytic mechanism?
What provides the scissile-bond specificity in the chymotrypsin catalytic mechanism?
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What is the role of the active-site histidine in the chymotrypsin catalytic mechanism?
What is the role of the active-site histidine in the chymotrypsin catalytic mechanism?
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What are the multiple catalytic strategies involved in the chymotrypsin catalytic mechanism?
What are the multiple catalytic strategies involved in the chymotrypsin catalytic mechanism?
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What is the function of the substrate-recognition site in chymotrypsin specificity?
What is the function of the substrate-recognition site in chymotrypsin specificity?
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What is the role of the oxyanion intermediate in the chymotrypsin catalytic mechanism?
What is the role of the oxyanion intermediate in the chymotrypsin catalytic mechanism?
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What is the function of the catalytic triad consisting of aspartate, histidine, and serine in chymotrypsin catalysis?
What is the function of the catalytic triad consisting of aspartate, histidine, and serine in chymotrypsin catalysis?
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What is the primary function of the hydrophobic binding pocket in chymotrypsin specificity?
What is the primary function of the hydrophobic binding pocket in chymotrypsin specificity?
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Study Notes
Enzyme Catalysis and Coenzymes
- Pepsin, a protease in the stomach, is a member of the aspartate protease superfamily, using two aspartate residues for acid-base catalysis.
- Aspartate proteases cannot use histidine for catalysis, unlike chymotrypsin.
- Enzymes in amino acid metabolism use pyridoxal phosphate derived from vitamin B6 for catalysis.
- Functional groups like coenzymes, metal ions, and metallocoenzymes are employed by enzymes for catalytic process.
- Almost all polar amino acids participate directly in catalysis, with some capable of covalent catalysis.
- Vitamin deficiencies result in loss of specific enzyme activities that depend on the coenzyme form of the vitamin.
- Coenzymes are tightly bound to enzymes and do not dissociate during the reaction.
- Ethanol inhibits the absorption of thiamin and displaces pyridoxal phosphate from its protein-binding sites.
- Coenzymes are usually synthesized from vitamins and participate in catalysis by providing functional groups.
- Coenzymes can be activation-transfer or oxidation-reduction coenzymes, with almost no catalytic power when not bound to the enzyme.
- Activation-transfer coenzymes participate in catalysis by forming a covalent bond with a portion of the substrate.
- Histidine's inability to extract a proton at low pH makes it unsuitable for general acid-base catalysis, unlike aspartic acid.
Enzyme Catalysis Mechanisms
- The serine hydroxyl group has a high pK, requiring enzyme structure to aid in proton removal and stabilization of the resulting oxygen anion at physiologic pH.
- The catalytic triad, consisting of aspartate, histidine, and serine, demonstrates cooperative interactions in the active site.
- The oxyanion tetrahedral transition-state complex in the reaction sequence is stabilized by hydrogen bonds with peptide backbone –NH groups.
- Enzymes like chymotrypsin form stable covalent intermediates during catalysis, involving serine or cysteine residues.
- The dissociating products of enzyme-catalyzed reactions are often destabilized by charge repulsion in the active site.
- Hydrolysis of the acyl–chymotrypsin intermediate involves the activation of water by the active-site histidine for a nucleophilic attack.
- Real enzymatic reactions result in a "multibump" energy diagram, with semistable covalent intermediates present as dips in the energy curve.
- Covalent catalysis involves the substrate being covalently linked to an amino acid side chain at the enzyme's active site during the reaction.
- Metal-ion catalysis, as seen in carbonic anhydrase, requires metal ions to allow catalysis to occur.
- Catalysis by approximation refers to the enzyme forcing substrates to bind in a manner that places reactive groups in the appropriate orientation for a reaction to occur.
- Nucleoside monophosphate kinases use catalysis by approximation to transfer a phosphate from a nucleoside triphosphate to a nucleoside monophosphate.
- Gastric acid in the stomach denatures proteins through disruption of ionic interactions and hydrogen bonding, lowering the pH to 1 to 2.
Chymotrypsin Catalytic Mechanism and Specificity
- Chymotrypsin is a serine protease that utilizes a serine in the active site to form a covalent intermediate during proteolysis.
- The hydrolysis reaction involves the addition of OH− from water to the carbonyl carbon of the peptide bond and an H+ to the N, cleaving the bond.
- Chymotrypsin catalyzes the reaction faster by using the hydroxyl group of a serine residue for the attack, activating it and stabilizing the oxyanion transition-state complexes.
- The reaction takes place in two stages: cleavage of the peptide bond in the substrate protein and hydrolysis of the acyl–enzyme intermediate.
- Specificity of binding to chymotrypsin involves hydrolyzing the peptide bond on the carbonyl side of specific amino acids in a denatured protein.
- The substrate-recognition site consists of a hydrophobic binding pocket that holds the hydrophobic amino acid contributing the carbonyl group of the scissile bond.
- Scissile-bond specificity is provided by the subsequent steps of the reaction, such as moving serine 195 into attacking position.
- In the first stage of the reaction, the peptide bond of the denatured protein substrate is cleaved as an active-site serine hydroxyl group attacks the carbonyl carbon.
- Aspartate and histidine cooperate in converting the hydroxyl group into a better nucleophilic attacking group by giving it a more negative charge.
- An active-site histidine acts as a base and abstracts a proton from the serine hydroxyl.
- The catalytic mechanism involves the formation of an oxyanion intermediate, stabilization of the N–H groups of serine 195 and glycine, and the use of histidine as a general base and acid catalyst.
- Chymotrypsin catalytic mechanism involves multiple catalytic strategies, including nucleophilic catalysis, acid–base catalysis, and stabilization of transition-state complexes.
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Description
Test your knowledge of enzyme catalysis, coenzymes, and the specific mechanisms involved in the catalytic activity of enzymes such as chymotrypsin. Explore topics like aspartate proteases, catalytic triads, oxyanion transition-state complexes, and the specificity of chymotrypsin binding.
