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Chapter 19: Problem 1

Describe the labeling pattern that would result from the introduction into the TCA cycle of glutamate labeled at \(\mathrm{C}_{\gamma}\) with \(^{14} \mathrm{C}\)Describe the labeling pattern that would result from the introduction into the TCA cycle of glutamate labeled at \(\mathrm{C}_{\gamma}\) with \(^{14} \mathrm{C}\)

Short Answer

Expert verified
The labeled gamma carbon of glutamate ends up being released as CO2 during the conversion of \(\alpha\)-ketoglutarate into succinyl-CoA in the first round of the TCA cycle.

Step by step solution

01

Transamination of Glutamate

Glutamate undergoes transamination, forming \(\alpha\)-ketoglutarate and releasing an amino group. This process involves the gamma carbon (labeled) becoming a carboxylate (\(-COO^-\)) group.
02

Understanding \(\alpha\)-Ketoglutarate Contribution to the TCA Cycle

\(\alpha\)-Ketoglutarate, now containing the labeled carbon atom enters the TCA cycle and goes through decarboxylation during the transformation into succinyl-CoA by alpha-ketoglutarate dehydrogenase complex. This results in the release of a molecule of CO2.
03

Tracking the Labeled C

The labeled gamma carbon of the original glutamate, now represented as a carboxylate in the \(\alpha\)-ketoglutarate, is the one that gets released as CO2 during the conversion of \(\alpha\)-ketoglutarate into succinyl-CoA in the first round of the TCA cycle.

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Most popular questions from this chapter

(Integrates with Chapter 3 .) Aconitase catalyzes the citric acid cycle reaction: Citrate \(\rightleftharpoons\) isocitrate The standard free energy change, \(\Delta G^{\circ \prime}\), for this reaction is +6.7 \(\mathrm{kJ} / \mathrm{mol}\). However, the observed free energy change \((\Delta G)\) for this reaction in pig heart mitochondria is \(+0.8 \mathrm{kJ} / \mathrm{mol}\). What is the ratio of [isocitrate]/[citrate] in these mitochondria? If [isocitrate] = \(0.03 \mathrm{m} M,\) what is [citrate]?

In a tissue where the TCA cycle has been inhibited by fluoroacetate, what difference in the concentration of each TCA cycle metabolite would you expect, compared with a normal, uninhibited tissue?

Describe the effect on the TCA cycle of (a) increasing the concentration of \(\mathrm{NAD}^{+},\) (b) reducing the concentration of \(\mathrm{ATP}\), and (c) increasing the concentration of isocitrate.

Glycolysis, the pyruvate dehydrogenase reaction, and the TCA cycle result in complete oxidation of a molecule of glucose to \(\mathrm{CO}_{2}\). Review the calculation of oxidation numbers for individual atoms in any molecule, and then calculate the oxidation numbers of the carbons of glucose, pyruvate, the acetyl carbons of acetyl-CoA, and the metabolites of the TCA cycle to convince yourself that complete oxidation of glucose involves removal of 24 electrons and that each acetyl-CoA through the TCA cycle gives up 8 electrons.

Aconitase is rapidly inactivated by \(2 R, 3 R\) -fluorocitrate, which is produced from fluoroacetate in the citrate synthase reaction. Interestingly, inactivation by fluorocitrate is accompanied by stoichiometric release of fluoride ion (i.e., one F-ion is lost per aconitase active site \() .\) This observation is consistent with "mechanism-based inactivation" of aconitase by fluorocitrate. Suggest a mechanism for this inactivation, based on formation of 4 -hydroxy-trans-aconitate, which remains tightly bound at the active site. To assess your answer, consult this reference: Lauble, H., Kennedy, M., et al., 1996. The reaction of fluorocitrate with aconitase and the crystal structure of the enzyme-inhibitor complex. Proceedings of the National Academy of Sciences \(93: 13699-13703\)
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