How is oxaloacetate conversion to phosphoenolpyruvate?

How is oxaloacetate conversion to phosphoenolpyruvate?

Phosphoenolpyruvate carboxykinase (PEPCK) is an enzyme in the lyase family used in the metabolic pathway of gluconeogenesis. It converts oxaloacetate into phosphoenolpyruvate and carbon dioxide. PDB rendering based on 1khb. It is found in two forms, cytosolic and mitochondrial.

How is oxaloacetate used in gluconeogenesis?

Malate is oxidized to oxaloacetate using NAD+ in the cytosol, where the remaining steps of gluconeogenesis take place. Oxaloacetate is decarboxylated and then phosphorylated to form phosphoenolpyruvate using the enzyme PEPCK. A molecule of GTP is hydrolyzed to GDP during this reaction.

What are the steps of phosphoenolpyruvate synthesis in gluconeogenesis?

11 steps:

  1. Steps 1 and 2: pyruvate. Glycolysis to phosphoenolpyruvate.
  2. Steps 3–8: phosphoenolpyruvate to fructose-1,6-bisphosphate.
  3. Step 9: dephosphorylation of fructose-1,6-bisphosphate to fructose-6-phosphate.
  4. Step 10: fructose-6-phosphate to glucose.
  5. Step 11: glucose.

Why must oxaloacetate be converted to malate in gluconeogenesis?

Because oxaloacetate cannot pass through the mitochondria membranes it must be first converted into malate by malate dehydrogenase. Malate can then cross the mitochondria membrane into the cytoplasm where it is then converted back into oxaloacetate with another malate dehydrogenase.

What phosphoryl donor is used in the reaction of converting oxaloacetate to phosphoenolpyruvate?

The phosphoryl donor in the formation of phosphoenolpyruvate is: pyruvate.

Can oxaloacetate be converted to pyruvate?

Under gluconeogenic conditions, the TCA cycle intermediates oxaloacetate or malate are converted to pyruvate and PEP by decarboxylation (C4-decarboxylation) [1, 4] and thus, the PEP–pyruvate–oxaloacetate node provides the direct precursors for gluconeogenesis.

Why is oxaloacetate important in the citric acid cycle?

Oxaloacetate is an intermediate of the citric acid cycle, where it reacts with acetyl-CoA to form citrate, catalyzed by citrate synthase. It is also involved in gluconeogenesis, the urea cycle, the glyoxylate cycle, amino acid synthesis, and fatty acid synthesis.

How is pyruvate converted to phosphoenolpyruvate in gluconeogenesis?

The conversion of pyruvate to phosphoenolpyruvate requires two enzymes in gluconeogenesis even though the reverse reaction in glycolysis required only one. The enzyme involved is pyruvate carboxylase, which requires ATP and converts pyruvate to oxaloacetate. Oxaloacetate is then converted to phosphoenolpyruvate.

How does oxaloacetate reduce malate?

In the cytosol, oxaloacetate is reduced to malate by electrons from NADH. Malate is then transported into the mitochondrial matrix via an oxaloacetate/malate antiporter. Inside the mitochondrion, malate is oxidized by NAD+ back to oxaloacetate forming NADH.

How is malate converted into oxaloacetate?

In order to get the oxaloacetate out of the mitochondria, malate dehydrogenase reduces it to malate, and it then traverses the inner mitochondrial membrane. Once in the cytosol, the malate is oxidized back to oxaloacetate by cytosolic malate dehydrogenase.

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