protease mechanism: you isolate a new protease which cleaves the peptide bond 2 aa residues before a F residue. You might expect to find. O An t residue in the S2'pocket OAL residue in the $2 pocket O aV residue in the oxyanion hole An Lresidue in the catalytic triad

Understanding the Mechanisms of Reactions Related to Transketolase The mechanistic chemistry of the acetolactate synthase and phosphoketolase reactions (shown here) is similar to that of the transketolase reaction (Figure 22.30). Write suitable mechanisms for these reactions.

Allosteric Regulation of Ribonucleotide Reductase by ATP and Deoxynucleotides Describe the underlying rationale for the regulatory effects exerted on ribonucleotide reductase by ATP, dATP, dTTP, and dGTP.

Distinguishing the Mechanisms of Class I and Class I Aldolases Fructose bisphosphate aldolase in animal muscle is a class 1 aldolase, which forms a Schiff base intermediate between substrate (for example. fructose-1, 6-bisphosphate or dihydroxyacetone phosphate) and a lysine at the active site (see Figure I8.12). The chemical evidence for this intermediate conies from studies with aldolase and the reducing agent sodium borohydride, NaBH4. Incubation of the enzyme with dihydroxyacetone phosphate and NaBH4 inactivates the enzyme. Interestingly, no inactivation is observed if NabH4 is added to the enzyme in the absence of substrate. Write a mechanism that explains these observations and provides evidence for the formation of a Schiff base intermediate in the aldolase reaction.

Energetic of Fructose-1 ,6-bis P Hydrolysis (Integrates with Chapter 3.) The standard free energy change (G) for hydrolysis of fructose-1. 6-bisphosphate (FBP) to fructose-S-phosphate (F-6-P) and P: is -16.7 KJ/mol: FBP + H2O fructose-6-P + Pi The standard free energy change (G) for ATP hydrolysis is -30.5 KJ/mol: ATP + H2O ADP + Pj What is the standard free energy change for the phosphofructokinase reaction: ATP + fructose-6-P ADP + FBP b. What is the equilibrium constant for this reaction? c. Assuming the intracellular concentrations of [ATP] and (ADP] are maintained constant at 4 mM and 1.6 mM, respectively, in a rat liver cell, what will be the ratio of [FBP]/[fructose-6-P] when the phosphofructokinase reaction reaches equilibrium?

Which of the following statements about inhibition is true? a. Allosteric inhibitors and allosteric activators are competitive for a given enzyme. b. If an inhibitor binds the active site, it is considered noncompetitive. c. If an inhibitor binds to a site other than the active site, this competitive inhibition. d. A noncompetitive inhibitor is believed to change the shape of the enzyme, making its active site inoperable. e. Competitive inhibition is usually not reversible.

Assessing the Effect of Active-Site Phosphorylation on Enzyme Activity (Integrates with Chapter 15.) The serine residue of isocitrate dehydroenase that is phosphorylated by protein kinase lies within the active site of the enzyme. This situation contrasts with most other examples of coa1ent modification by protein phosphorylation. where the phosphorylation occurs at a sate remote from the active site. What direct effect do you think such active-site phosphorylation might have on the catalytic activity of isocitrate dehydrogcn.ise? (Sec Barford, D., 1991. Molecular mechanisms for the control of enzymic activity by protein phosphorytation. Biochimica et Biophysica Acta 1133:55—62.)

Why Do Anabolic and Catabolic Pathways Differ? Why is the pathway for the biosynthesis of a biomolecule at least partially different from the pathway for its catabolism? Why is the pathway for the biosynthesis of a biomolecule inherently more complex than the pathway for its degradation?

Which of the following statements about the allosteric site is true? a. The allosteric site is a second active site on a substrate in a metabolic pathway. b. The allosteric site on an enzyme can allow the product of a metabolic pathway to inhibit that enzyme and stop the pathway. c. When the allosteric site of an enzyme is occupied, the reaction is irreversible and the enzyme cannot react again. d. An allosteric activator prevents binding at the active site. e. An enzyme that possesses allosteric sites does not possess an active site.

Understanding the Mechanism of the -Ketoglutarate Dehydrogenase Reaction tshe first step of the -Ketoglutarate dehydrogenase reaction involves decarboxylation of the substrate and leaves a covalent TPP intermediate. Write a reasonable mechanism for this reaction.