Mechanism and Activity
The active site of malate dehydrogenase is a hydrophobic cavity within the protein complex that has specific binding sites for the substrate and its coenzyme, NAD+. In its active state, MDH undergoes a conformational change that encloses the substrate to minimize solvent exposure and to position key residues in closer proximity to the substrate. The three residues in particular that comprise a catalytic triad are histidine (His-195), aspartate (Asp-168), both of which work together as a proton transfer system, and arginines (Arg-102, Arg-109, Arg-171), which secure the substrate. Kinetic studies show that MDH enzymatic activity is ordered. NAD+/NADH is bound before the substrate.
Note: the structure of malate in the figure above is not correct. Malate should have four carbons, not six as the figure implies.
Read more about this topic: Malate Dehydrogenase
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