Final answer:
The mitochondrial malic enzyme that participates in pyruvate metabolism and produces NAD+ is ME3. This enzyme helps maintain cellular redox balance and contributes to ATP production in the citric acid cycle.
Step-by-step explanation:
The malic enzyme that participates in pyruvate metabolism in mitochondria and produces NAD+ is ME3. This enzyme, also known as mitochondrial NAD(P)-dependent malic enzyme, is primarily involved in the conversion of malate into pyruvate. This process not only produces NAD+ but also contributes CO2 and can supply NADPH in certain organisms. Producing NAD+, however, is critical for the cell's redox balance and is especially important during the citric acid cycle, which is tightly connected to pyruvate metabolism as it produces various coenzymes like NADH and FADH2 that are essential for ATP production during oxidative phosphorylation.
Malic enzymes are found in different isoforms, such as ME1 (cytosolic), ME2 (mitochondrial), and ME3 (also mitochondrial, NAD+-dependent), where the ME2 isoform is NADP+-dependent. The consumption of NAD+ in reactions catalyzed by ME3 and similar enzymes helps to facilitate the flow of electrons through the electron transport chain, leading to ATP synthesis. The malate dehydrogenase (MDH) enzyme also plays a crucial role in the citric acid cycle, converting malate into oxaloacetate and producing NADH, a necessary step for the continuation of the cycle that generates large amounts of ATP. However, MDH should not be confused with ME3, as both catalyze different reactions involving malate.