Malate dehydrogenase

Definition

Malate dehydrogenase is an enzyme that catalyzes the reversible conversion of malate to oxaloacetate while reducing NAD+ to NADH. This enzyme plays a crucial role in various metabolic pathways, particularly in the citric acid cycle and gluconeogenesis, linking carbohydrate metabolism with cellular respiration and energy production.

5 Must Know Facts For Your Next Test

1. Malate dehydrogenase exists in two forms: mitochondrial and cytosolic, allowing it to function in different cellular environments.
2. The reaction catalyzed by malate dehydrogenase is crucial for maintaining the balance of metabolites in the citric acid cycle.
3. This enzyme is regulated by the concentration of its substrates (malate and oxaloacetate) and products (NADH and NAD+), demonstrating a classic example of feedback regulation.
4. Malate dehydrogenase plays a significant role in the malate-aspartate shuttle, which helps transport reducing equivalents across the mitochondrial membrane.
5. Deficiencies or malfunctions in malate dehydrogenase can lead to metabolic disorders, emphasizing its importance in cellular metabolism.

Review Questions

• How does malate dehydrogenase contribute to the overall functioning of the citric acid cycle?
  • Malate dehydrogenase contributes to the citric acid cycle by catalyzing the conversion of malate to oxaloacetate. This reaction is vital as it not only completes one turn of the cycle but also generates NADH, which is essential for ATP production via oxidative phosphorylation. The enzyme’s activity ensures a continuous flow of substrates and products through the cycle, facilitating efficient energy extraction from carbohydrates.
• Discuss how malate dehydrogenase is involved in gluconeogenesis and its significance during fasting.
  • Malate dehydrogenase plays a key role in gluconeogenesis by catalyzing the conversion of malate back into oxaloacetate. During fasting or periods of low carbohydrate intake, this process is critical for maintaining blood glucose levels. The regeneration of oxaloacetate enables further conversion into phosphoenolpyruvate, which ultimately leads to glucose synthesis, providing energy for cells when dietary glucose is not available.
• Evaluate the impact of malate dehydrogenase dysfunction on metabolic pathways and overall energy balance in cells.
  • Dysfunction in malate dehydrogenase can disrupt metabolic pathways such as the citric acid cycle and gluconeogenesis, leading to imbalances in metabolite levels. For instance, if the enzyme's activity is compromised, there may be an accumulation of malate and a shortage of oxaloacetate, hindering ATP production. This can result in decreased energy availability for cellular processes and may contribute to metabolic disorders, highlighting the enzyme's importance for maintaining energy homeostasis.

Related terms

Citric Acid Cycle: A series of enzymatic reactions that generates energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

NADH:

A reduced form of nicotinamide adenine dinucleotide, which acts as an electron carrier in cellular respiration, transporting electrons to the electron transport chain.

Gluconeogenesis: The metabolic pathway that results in the generation of glucose from non-carbohydrate precursors, important during fasting or low-carbohydrate intake.