Question

As part of the malate‑aspartate shuttle, the malate–α‑ketoglutarate transporter transfers malate formed in the cytosol to the mitochondrion. The malate–α‑ketoglutarate transporter is inhibited by n‑butylmalonate. When n‑butylmalonate is added to an aerobic suspension of kidney cells using glucose as the primary source of energy, ATP synthesis drastically decreases

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1 - Inhibiting the malate-aspartate shuttle will result in the accumulation of NADH in the cytosol. High levels cytosolic NADH will initiate gluconeogenesis.

2 - Blocking the malate–α‑ketoglutarate transporter will dissipate the electrical gradient across the mitochondrial membrane, thus uncoupling ATP synthesis from the respiratory chain.

3 - If the malate-aspartate shuttle is inhibited, NADH will accumulate in the cytosol, thus limiting the amount of NADH available for the electron-transfer chain. Decreasing the amount of NADH in the mitochondrion will eventually inhibit oxidative phosphorylation.

4 - Inhibiting the malate–α‑ketoglutarate transporter will prevent the regeneration of NAD+NAD+ by the malate-aspartate shuttle in the cytosol, thus forcing the kidney cells to switch to anaerobic glycolysis via lactate fermentation.

5 - Inhibiting the malate–α‑ketoglutarate transporter will limit the amount of malate available for the citric acid cycle, thus slowing down oxidative phosphorylation.

Answer 1

Answers to check:

3 - If the malate-aspartate shuttle is inhibited, NADH will accumulate in the cytosol, thus limiting the amount of NADH available for the electron-transfer chain. Decreasing the amount of NADH in the mitochondrion will eventually inhibit oxidative phosphorylation.

4 - Inhibiting the malate–α‑ketoglutarate transporter will prevent the regeneration of NAD+NAD+ by the malate-aspartate shuttle in the cytosol, thus forcing the kidney cells to switch to anaerobic glycolysis via lactate fermentation.

NADH can only be transferred to mitochondria by the malate- aspartate shuttle exclusively when the NADH to NAD⁺ ratio is greater in the cytosol compare to matrix as shown in below image. If NADH will accumulate in the cytosol, this forces glycolysis to operate anaerobically with reoxidation of NADH in the lactate dehydrogenase reaction. ATP is not formed aerobically and decreases drastically, to 2 ATP per glucose molecule.

NADH + H+ NAD Aspartate Oxaloacetate Malate a-ketoglutarate Glutamate Cytosol Matrix c-ketoglutarate Glutamate Aspartate Oxaloacetate Malate NADH+H+ NAD

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