The oxidation of malate by NAD+ to form oxaloacetate is a highly endergonic reaction under standard conditions.AG +29 kJ mol¹ (+7 kcal mol-¹)Malate + NAD+ oxaloacetate + NADH + H+The reaction proceeds readily under physiological conditions.=Why does the reaction proceed readily as written under physiological conditions?The NADH produced during glycolysis drives the reaction in the direction of malate oxidation.The steady-state concentrations of the products are low compared with those of the substrates.The reaction is pushed forward by the energetically favorable oxidation of fumarate to malate.Endergonic reactions such as this occur spontaneously without the input of free energy.Assuming an [NAD+ ]/[NADH] ratio of 8, a temperature of 25°C, and a pH of 7, what is the lowest [malate]/[oxaloacetate] ratioat which oxaloacetate can be formed from malate?[malate][oxaloacetate]

Because oxaloacetate is kept at low concentrations, the reaction progresses and the actual ΔG is…

Answered: The oxidation of malate by NAD+ to form…

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter25: Nitrogen Acquisition And Amino Acid Metabolism

Section: Chapter Questions

Problem 22P

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The Reactions and Meehanisms of the Leloir Pathway Write the reactions that permit galactose to be utilized in glycolysis. Write a suitable mechanism, tor one of these reactions.
Using the ActiveModel for enoyl-CoA dehydratase, give an example of a case in which conserved residues in slightly different positions can change the catalytic rate of reaction.
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.
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.
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.
Examine the ActiveModel for alcohol dehydrogenase and describe the structure and function of the catalytic zinc center.
Energetics of the Hexokinase Reaction The standard-state free energy change. Gfor the hexokinase reaction, is â€” 1 6.7 kJ/mol. Use the values in Table I to calculate the value of Gfor this reaction in the erythrocyte at 37Â°C.
The Effect of lodoacetic Acid on the Glyceraldehyde-3-P Dehydrogenase Reaction (Integrates with Chapters 4 and 14.) How might iodoacetic acid affect the glyceraldehydes-3-phosphate dehydrogenase reaction in glycolysis? Justify your answer.
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?
Based on your residing of this chapter, what would you expect to be the most immediate effect oil glycolysis, if the steady-state concentration of gJucose-6-P were 8.3 mM instead of 0.083 mM?
Comparing Glycolysis Entry Points for Sucrose Sucrose can enter glycolysis by either of two routes: Sucrose phosphorylase: Sucrose + Pi fructose + glucose-1-phosphate Invertase: Sucrose + H20 fructose + glucose Would either of these reactions offer Jin advantage over the other In the preparation of hexoses fur entry into glycolysis?
Ethanol as a Source of Metabolic Energy (Integrates with Chapters 19 and 20.) Acetate produced in ethanol metabolism can be transformed into acetyl-COA by the acetyl thiokinase reaction: Acetate+ATP+CoASHacetyleCoA+AMP+PPiAcetyle-CoA then can enter the citric acid cycle and undergo oxidation to 2 CO2by this route, assuming oxidative phosphorylation is part of the process? (Assume all reactions prior to acetyl-CoA entering the citric acid cycle occur outside the mitochondrion). Per carbon atom, which is a better metabolic fuel, ethanol or glucose? That is, how many ATP equivalents per carbon atom are generated by combustion of glucose versus ethanol to CO2?

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