Aconitase catalyzes the reaction: citrate ↔ HisocitrateThe standard free energy change, ΔG°′, for this reaction is +6.3 kJ/mol.However, the observed free energy change (ΔG) for this reaction in mammalian mitochondria at 25°C is ∼0 kJ>mol (Table 13.2).(a) Calculate the ratio of [isocitrate]>[citrate] in mitochondria.(b) Is this reaction likely to be a control point for the citric acid cycle? Whyor why not? TABLE 13.2 Reactions of the citric acid cycleAG"AGReactionEnzyme(kJ/mol)(kJ/mol)1.Acetyl-CoA + oxaloacetate + H2Ocitrate + CoA-SH + H+Citrate synthase-32.2--552а.Citrate cis-aconitate + H,OAconitase+6.32b.cis-Aconitate + H20isocitrateAconitase3.Isocitrate + NADa-ketoglutarate + CO2 + NADHIsocitrate dehydrogenase-11.6--20a-Ketoglutaratedehydrogenase complex4.a-Ketoglutarate + NAD+ + CoA-SH =succinyl-CoA + CO2 + NADH-33.5-405.Succinyl-CoA + P + ADP (GDP)succinate + ATP (GTP) + CoA-SHSuccinyl-CoA synthetase-3.8-06.Succinate + FAD (enzyme-bound)fumarate + FADH2 (enzyme-bound)Succinate dehydrogenase7.Fumarate + H202 L-malateFumarase-3.88.L-Malate + NAD+oxaloacetate + NADH + H+Malate dehydrogenase+29.7Net-48.0115Note: AG°' value for reaction 3 was calculated from the E' values for a-ketoglutarate/isocitrate (-0.38 V) and NAD/NADH (-0.32 V).

The free energy, delta G can be determined from standard free energy change, ΔG0 with this reaction:…

Answered: TABLE 13.2 Reactions of the citric acid…

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter19: The Tricarboxylic Acid Cycle

Section: Chapter Questions

Problem 21P: Complete oxidation of a 16-carbon fatty acid can yield 129 molecules of ATP Study Figure 19.2 and...

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Aconitase catalyzes the reaction: citrate ↔ Hisocitrate
The standard free energy change, ΔG°′, for this reaction is +6.3 kJ/mol.
However, the observed free energy change (ΔG) for this reaction in mammalian mitochondria at 25°C is ∼0 kJ>mol (Table 13.2).
(a) Calculate the ratio of [isocitrate]>[citrate] in mitochondria.
(b) Is this reaction likely to be a control point for the citric acid cycle? Why
or why not?

TABLE 13.2 Reactions of the citric acid cycle
AG"
AG
Reaction
Enzyme
(kJ/mol)
(kJ/mol)
1.
Acetyl-CoA + oxaloacetate + H2O
citrate + CoA-SH + H+
Citrate synthase
-32.2
--55
2а.
Citrate cis-aconitate + H,O
Aconitase
+6.3
2b.
cis-Aconitate + H20
isocitrate
Aconitase
3.
Isocitrate + NAD
a-ketoglutarate + CO2 + NADH
Isocitrate dehydrogenase
-11.6
--20
a-Ketoglutarate
dehydrogenase complex
4.
a-Ketoglutarate + NAD+ + CoA-SH =
succinyl-CoA + CO2 + NADH
-33.5
-40
5.
Succinyl-CoA + P + ADP (GDP)
succinate + ATP (GTP) + CoA-SH
Succinyl-CoA synthetase
-3.8
-0
6.
Succinate + FAD (enzyme-bound)
fumarate + FADH2 (enzyme-bound)
Succinate dehydrogenase
7.
Fumarate + H20
2 L-malate
Fumarase
-3.8
8.
L-Malate + NAD+
oxaloacetate + NADH + H+
Malate dehydrogenase
+29.7
Net
-48.0
115
Note: AG°' value for reaction 3 was calculated from the E' values for a-ketoglutarate/isocitrate (-0.38 V) and NAD/NADH (-0.32 V).

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