Lactate Dehydrogenase

spinqualitylabelsall models Lactate dehydrogenase dimer complex with cofactor NAD and pyruvate (PDB code 4nd4) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Function L-lactate dehydrogenase (L-LDH) catalyzes the interconversion of pyruvate and NADH+ to L-lactate and NAD+. H-lactate dehydrogenase (H-LDH) catalyzes the interconversion of D-lactate and ferricytochrome c to pyruvate and ferrocytochrome c. Lactate Dehydrogenase (LDH) is an important enzyme in humans. It occurs in different regions of the body, each region having a unique conformation of different subunits. LDH is a key enzyme in anaerobic respiration. Anaerobic Respiration is the conversion of pyruvate into lactate acid in the absence oxygen. This pathway is important to glycolysis in two main ways. The first is that if pyruvate were to build up glycoysis and thus the generation of ATP would slow. The second is anaerobic respiration allows for the regeneration of NAD+ from NADH. NAD+ is required when glyceraldehyde-3-phosphate dehydrogenase oxidizes glyceraldehyde-3-phosphate in glycolysis, which generates NADH. Lactate dehydrogenase is responsible for the anaerobic conversion of NADH to NAD+. Click here to see the residues which form interactions with pyruvate in the Lactate Dehydrogenase from Cryptosporidium parvum (4nd4). See also: Cori cycle, Gluconeogenesis. Human Lactate Dehydrogenase Structure Human LDH is a quaternary protein formed of the combination of two subunits, M and H (Muscle and Heart) into a structure of four of the subunits. The various combinations found in the human body are: (4H) Heart (3H1M) Reticuloendothelial (2H2M) Lungs (1H3M) Kidneys (4M) Muscle and Liver The secondary structure of LDH as shown here is comprised of 40% alpha helices and 23% beta sheets. The SCOP data classifies this form of lactate dehydrogenase as mixed beta-alpha-beta, with mainly parallel beta sheets. See also Human Lactate Dehydrogenase Jasper Lactate Final Rossmann fold. Catalysis Studies have shown that the reaction mechanism of LDH follows an ordered sequence. In order for lactate to be oxidized NADH must bind to the enzyme first followed by lactate. Several residues are involved in the binding of NADH. Once the NADH is bound to the enzyme, it is then possible for lactate to bind (substrate oxamate is shown; the ‑CH3 group is replaced by ‑NH2 to form oxamate). Lactate binds to the enzyme between the nicotinamide ring and several LDH residues. Transfer of a hydride ion then happens quickly in either direction giving a mixture of the two tertiary complexes, enzyme-NAD+-lactate and enzyme-NADH-pyruvate .Finally pyruvate dissociates from the enzyme followed by NAD+. Kinetics Kinetic studies of lactate dehydrogenase with oxalate and oxamate (structural analogues of lactate and pyruvate)have proven the mechanism stated above. The rate limiting step in this reaction is the rate of dissociation of NAD+ and NADH. The conversion of pyruvate to lactate with the subsequent regeneration of NAD+ is very favorable. Regulation As the mechanism is one of equilibrium, There appears to be no regulation specifically designed for lactate dehydrogenase, instead it is dependent on the activation of anaerobic reparation and the presence of pyruvate and NADH, or lactate and NAD+. 3D structures of lactate dehydrogenase Lactate dehydrogenase 3D structures

Additional Information

For additional information, see 4nd4

Reference

• 1- https://www.jbc.org/content/243/17/4526.full.pdf+html

Proteopedia Page Contributors and Editors (what is this?)

Jasper Small, Michal Harel, Alexander Berchansky, David Canner, Ann Taylor, Joel L. Sussman