Subunits malate dehydrogenase

Malic enzyme (malate dehydrogenase (decarboxylating), EC 1.1.1.39) catalyzes reversible oxidative decarboxylation of malate to pyruvate. The enzyme uses NAD+ as an electron acceptor, but it is also able to utilize NADP+ with lower affinity (Drmota et al. 1996). With a subunit size of approximately 63 kDa, the Trichomonas hydrogenosomal malic enzyme belongs to the family of large, eukaryotic type of malic enzymes. In contrast, the approximately 40-kDa-subunit malic enzyme, located in the cytosol, belongs... 

Fig. 20. Chain trace of pig heart soluble malate dehydrogenase subunit. Stereo drawing from lhe work of... 

Figure 9.8. The malate dehydrogenase dimer, indicating the location of the active sites in each protein plus the dimer interface. Malate dehydrogenase demonstrates substrate inhibition that has been attributed to subunit interactions and allosteric regulation by citrate, although the crystal structure of the protein reveals the absence of a separate allosteric site for citrate. See color insert.

When an enzyme contains multiple subunits and the reaction which it catalyzes involves multiple substrates, detailed steps in the cataljrtic processes may become very complicated. The malate dehydrogenases from mammals contain two subunits, and the substrates include both a form of the dicarboxylic acid and the dinucleotide coenzyme. The third... 

We have already described the purification of a chloroplastic NADP-malate dehydrogenase (Ferte et al., 1982). It is a 56 000 daltons dimeric protein made up of two apparently identical subunits. This enzyme plays an important role in the generation of reducing power used in the reduction cytoplasmic reactions. NADPH from photosynthesis reduces oxaloacetate to malate in the stroma. This reaction is catalyzed by NADP-MDH. A malate translocator exports this acid outside the chloroplast where NAD-MDH generates NADH. 

Malate dehydrogenase Complex alkylation 1-Trp-residue per subunit is modified in 8M urea with inactivation of the enzyme im... 

This dimeric enzyme (subunit 35000) catalyses a reaction similar to the lactate dehydrogenase reaction, and the subunit structures of the enzymes are strikingly similar [83-85] (Fig. 20). Crystallographic [85] and other [86] evidence suggests that the reaction mechanisms are similar. The 4-pro-R hydrogen of NADH is transferred to the Re side of the oxaloacetate to give L-malate [87],... 

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