Malate dehydrogenase

Definition

Malate dehydrogenase is an enzyme that catalyzes the reversible conversion of malate to oxaloacetate, while reducing NAD+ to NADH in the process. This enzyme plays a crucial role in the citric acid cycle, facilitating energy production by linking the cycle's reactions and contributing to cellular respiration. By participating in the interconversion of key metabolic intermediates, malate dehydrogenase is essential for maintaining the flow of carbon and energy through the cycle.

5 Must Know Facts For Your Next Test

1. Malate dehydrogenase exists in two forms: mitochondrial and cytosolic, each located in different cellular compartments with distinct functions.
2. The reaction catalyzed by malate dehydrogenase is an essential step in regenerating oxaloacetate, which is crucial for continuing the citric acid cycle.
3. NADH produced by malate dehydrogenase can be used in the electron transport chain to generate ATP, making it vital for energy production.
4. The activity of malate dehydrogenase can be influenced by factors such as pH, temperature, and substrate concentration, which can affect overall metabolic rates.
5. In addition to its role in the citric acid cycle, malate dehydrogenase is involved in gluconeogenesis, contributing to the formation of glucose from non-carbohydrate sources.

Review Questions

• How does malate dehydrogenase facilitate the continuation of the citric acid cycle?
  • Malate dehydrogenase facilitates the continuation of the citric acid cycle by catalyzing the conversion of malate to oxaloacetate while simultaneously reducing NAD+ to NADH. This reaction is critical because it regenerates oxaloacetate, which is necessary for combining with acetyl-CoA to form citrate and re-entering the cycle. Without this enzyme's function, the cycle would halt due to the depletion of oxaloacetate.
• Discuss the significance of NADH produced by malate dehydrogenase in cellular respiration.
  • NADH produced by malate dehydrogenase is significant because it serves as an important electron carrier that enters the electron transport chain during cellular respiration. The electrons carried by NADH are used to drive ATP synthesis through oxidative phosphorylation. Thus, malate dehydrogenase not only aids in the citric acid cycle but also plays a pivotal role in overall energy production within the cell.
• Evaluate how alterations in malate dehydrogenase activity could impact metabolic processes within a cell.
  • Alterations in malate dehydrogenase activity can significantly impact metabolic processes within a cell by disrupting both the citric acid cycle and gluconeogenesis. If activity is decreased, there may be insufficient regeneration of oxaloacetate, leading to reduced energy production and metabolic dysregulation. Conversely, increased activity could enhance energy output but might lead to imbalances in substrate availability for other metabolic pathways. Therefore, maintaining proper malate dehydrogenase function is crucial for overall cellular metabolism.

Related terms

NAD+: Nicotinamide adenine dinucleotide, a coenzyme that acts as an electron carrier in redox reactions, essential for energy metabolism.

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

Oxaloacetate: A four-carbon compound that serves as a substrate and product in several metabolic pathways, including the citric acid cycle.