Malate dehydrogenase

Definition

Malate dehydrogenase is an enzyme that catalyzes the reversible conversion of malate to oxaloacetate in the presence of NAD+ as a cofactor. This reaction plays a crucial role in cellular respiration, particularly in the context of converting pyruvate into usable energy within the mitochondria, connecting the oxidation of pyruvate and the citric acid cycle.

5 Must Know Facts For Your Next Test

1. Malate dehydrogenase is found in two forms: mitochondrial and cytosolic, allowing it to play roles in both mitochondrial and cytosolic metabolic pathways.
2. The enzyme facilitates the reduction of NAD+ to NADH during the conversion of malate to oxaloacetate, which is critical for energy production.
3. Malate dehydrogenase operates within the citric acid cycle by regenerating oxaloacetate, thus enabling the cycle to continue its function in energy metabolism.
4. The activity of malate dehydrogenase is regulated by substrate availability and product concentration, ensuring proper metabolic control.
5. Malate dehydrogenase is involved in the malate-aspartate shuttle, a mechanism that transports reducing equivalents across the mitochondrial membrane.

Review Questions

• How does malate dehydrogenase contribute to the overall process of cellular respiration?
  • Malate dehydrogenase plays a vital role in cellular respiration by catalyzing the conversion of malate to oxaloacetate. This reaction not only regenerates oxaloacetate, which is essential for the continuation of the citric acid cycle but also facilitates the reduction of NAD+ to NADH. The production of NADH is crucial as it carries electrons to the electron transport chain, ultimately contributing to ATP production and energy generation within cells.
• Discuss the significance of malate dehydrogenase's regulation in metabolic pathways.
  • The regulation of malate dehydrogenase is important for maintaining metabolic balance within cells. It responds to changes in substrate levels and product concentrations, which helps to prevent metabolic bottlenecks. When malate levels are high, it promotes conversion to oxaloacetate, while increased oxaloacetate can inhibit its activity. This fine-tuning ensures efficient energy production and prevents excessive accumulation of intermediates that could disrupt cellular metabolism.
• Evaluate how malate dehydrogenase's function impacts both mitochondrial metabolism and energy production.
  • Malate dehydrogenase significantly impacts mitochondrial metabolism and energy production through its role in the citric acid cycle and the malate-aspartate shuttle. By converting malate to oxaloacetate, it not only allows for continuous progression through the citric acid cycle but also aids in transporting reducing equivalents into mitochondria. This ensures that NADH is produced efficiently for ATP synthesis via oxidative phosphorylation, linking carbohydrate metabolism directly to energy output and highlighting its essential function in bioenergetics.

Related terms

Oxaloacetate: A four-carbon dicarboxylic acid that acts as a key intermediate in the citric acid cycle, formed from the decarboxylation of malate by malate dehydrogenase.

NAD+: Nicotinamide adenine dinucleotide, a coenzyme that serves as an electron carrier in redox reactions, playing a vital role in energy metabolism.

Citric Acid Cycle: Also known as the Krebs cycle, it is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.