Malátdehidrogénáz

Malátdehidrogénáz, often abbreviated as MDH, is an enzyme that catalyzes the reversible oxidation of L-malate to oxaloacetate. This reaction is a crucial step in several metabolic pathways, most notably the citric acid cycle (also known as the Krebs cycle or TCA cycle) and the malate-aspartate shuttle. In the citric acid cycle, MDH plays a role in regenerating oxaloacetate, which is essential for the cycle to continue. The malate-aspartate shuttle is important for transporting reducing equivalents (in the form of NADH) from the cytoplasm into the mitochondria, where they can be used in the electron transport chain for ATP production.

MDH is a widespread enzyme found in virtually all living organisms, from bacteria to eukaryotes. Different isoforms of malátdehidrogénáz exist, with distinct cellular localizations and kinetic properties, reflecting their specific roles in metabolism. For example, mitochondrial MDH is primarily involved in the citric acid cycle, while cytoplasmic MDH participates in the malate-aspartate shuttle and gluconeogenesis. The enzyme requires a cofactor, typically NAD+ or NADP+, to accept the electrons during the oxidation reaction. The reduction of oxaloacetate back to malate, also catalyzed by MDH, is important for replenishing malate levels and plays a role in processes like photosynthesis in plants, where it is involved in the Calvin cycle and photorespiration. The enzyme's activity can be influenced by substrate concentrations, pH, and the presence of inhibitors.