The preferred substrate is T because the enzyme half-saturates at 7.00 mM for T, but requires 28.0 mM for U, and 112 mM for S. b Question Content Area The rate constant k 2 with substrate S is 9.60×107 sec-1, with substrate T, k 2 = 6.00×104 sec-1, and with substrate U, k 2 = 2.40×106 sec-1. Calculate the catalytic efficiency with S, T, and U. Catalytic efficiency with S =  Catalytic efficiency with T =   Catalytic efficiency with U =   Does enzyme A use substrate S, substrate T, or substrate U with greater catalytic efficiency?

Using the ActiveModel for aldose reductase, describe the structure of the TIM barrel motif and the structure and location of the active site.

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.

Figure 27.3 illustrates the response of R (ATP-regenerating) and U (ATP-utilizing) enzymes to energy charge. a. Would hexokinase be an R enzyme or a U enzyme? Would glutamine: PRPP amidotransferase, the second enzyme in purine biosynthesis, be an R enzyme or a U enzyme? b. If energy charge = 0.5: Is the activity of hexokinase high or low? Is ribose-5-P pyrophosphokinase activity high or low? c. If energy charge = 0.95: Is the activity of hexokinase high or low? Is ribose-5-P pyrophosphokinase activity high or low?

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.

Based on your knowledge of the structure of NAD+ and an assumption that coenzyme dissociation is the rate limiting step of the alcohol dehydrogenase mechanism, hypothesize why a N249W mutation at the coenzyme binding site would increase the rate of catalysis.

The Catabolism of Uric Acid Write a balanced equation for the oxidation of uric acid to glyoxylic acid, CO2, and NH3, showing each step in the process and naming all of the enzymes involved.

Characterizing Glycolysis List the reactions of glycolysis that a. are energy consuming (under standard-stale conditions), b. are energy yielding (under standard-state conditions), c. consume ATP. d. yield ATP e. are strongly influenced by changes in concentration of substrate and product because of their molecularity. f. are at or near equilibrium in the erythrocyte (see Table 18.2).

Using the ActiveModel for phosphofructokinase (Trypanosoma), describe the difference between the APO1, AP02, and holoenzyme conformations.

Extending the Mechanism of Methylmalonyl-CoA Mutase to Similar Reactions Based on the mechanism for the methylmalonyl-CoA mutase (see problem 14), write reasonable mechanisms for the following reactions shown.