malaattidehydrogenaasin

Malaattidehydrogenaasi, often abbreviated as MDH, is an enzyme that plays a crucial role in intermediary metabolism. It catalyzes the reversible interconversion of malate and oxaloacetate. This reaction is a key step in both the citric acid cycle (also known as the Krebs cycle or TCA cycle) and gluconeogenesis. In the citric acid cycle, MDH catalyzes the last step, oxidizing malate to oxaloacetate, which then condenses with acetyl-CoA to start a new cycle. In gluconeogenesis, the reverse reaction, the reduction of oxaloacetate to malate, is facilitated by MDH.

There are several isoforms of malate dehydrogenase found in different cellular compartments. Mitochondrial malate dehydrogenase (mMDH) is primarily involved in the citric acid cycle. Cytosolic malate dehydrogenase (cMDH) participates in pathways such as gluconeogenesis and the malate-aspartate shuttle, which helps transport reducing equivalents from glycolysis in the cytoplasm into the mitochondria. Plant cells also possess additional MDH isoforms that are important for photosynthesis, particularly in the Calvin cycle and photorespiration. The enzyme typically uses NAD+ or NADP+ as a cofactor. The specific cofactor used can depend on the isoform and the direction of the reaction. Malate dehydrogenase is a ubiquitous enzyme found in most aerobic organisms.