Disease relevance of MDH2

• The molecular chaperones GroEL and GroES were produced at very high levels in Escherichia coli, purified, and shown to protect pig mitochondrial malate dehydrogenase (MDH) against thermal inactivation in vitro [1].
• Structures from pig heart cytosolic and Thermus flavus malate dehydrogenases (cMDH, Tf MDH), two proteins showing a 55% sequence homology, were compared with the aim of increasing cMDH stability using features from the Thermus flavus enzyme [2].

High impact information on MDH2

• It contains a putative AHL topogenic signal for microbody import and has no sequence similarity to the 27-residue-long presequence of the watermelon mitochondrial malate dehydrogenase precursor [3].
• Formation of a bienzyme complex of pig heart mitochondrial malate dehydrogenase and citrate synthase in a buffered system is demonstrated by means of a covalently attached fluorescent probe to citrate synthase [4].
• We have since determined the polypeptide chain conformation and coenzyme binding site of crystalline porcine heart mitochondrial malate dehydrogenase by x-ray diffraction methods [5].
• In a previous study, we reported the apparent similarity between a low resolution electron density map of mitochondrial malate dehydrogenase and a model of cytoplasmic malate dehydrogenase (Roderick, S. L., and Banaszak, L. J. (1983) J. Biol. Chem. 258, 11636-11642) [5].
• The overall polypeptide chain conformation of the enzyme, the location of the coenzyme binding site, and the preliminary location of several catalytically important residues have confirmed the structural similarity of mitochondrial malate dehydrogenase to cytoplasmic malate dehydrogenase and lactate dehydrogenase [5].

Chemical compound and disease context of MDH2

• 0.4 M myo-Inositol was observed to raise the melting temperature (Tm) of GS from E. coli by 3.9 degrees C and MDH from pig heart by 3.4 degrees C, respectively [6].
• Cpn60-(His)(6) mediated refolding of guanidine hydrochloride unfolded pig heart malic dehydrogenase (MDH) and Thermus flavus MDH at 25 and 70 degrees C, respectively, in an ATP-dependent manner [7].
• Guanidinium chloride (GdmCl) unfolding experiments showed that there is only about a 4.2-kjoule/mol difference in delta G 0 between the pig and Thermus MDH [8].

Biological context of MDH2

• A cDNA clone, named ppmMDH-1 and covering a part of the porcine mitochondrial malate dehydrogenase (mMDH; L-malate:NAD+ oxidoreductase, EC 1.1.1.37) mRNA, was isolated from a porcine liver cDNA library with a mixture of 24 oligodeoxyribonucleotides as a probe [9].
• Subunit interactions in mitochondrial malate dehydrogenase. Kinetics and mechanism of reassociation [10].
• The complete amino acid sequence of mitochondrial malate dehydrogenase from rat heart has been determined by chemical methods [11].
• Mitochondrial malate dehydrogenase and citrate synthase are sequential enzymes in the Krebs tricarboxylic acid cycle [12].
• Comparison of the molecular structures of cytoplasmic and mitochondrial malate dehydrogenase [13].

Anatomical context of MDH2

• Similar interactions to those described may occur in situ when mitochondrial malate dehydrogenase is transported to the mitochondrial matrix from its site of synthesis on cytosolic ribosomes [14].
• Hydrophobic interaction between the monomer of mitochondrial malate dehydrogenase and phospholipid membranes [14].
• Tissue origin of MDH isozymes in blood serum of rats exposed to alkylmercurials [15].
• For example, brain and spinal cord MDH immunoreactivity increased with intense staining in the cell bodies and fibers of neurons from the 6th to the 13th postnatal day; immunoreactivity gradually diminished into adulthood [16].
• Activities of the mitochondrial (m-MDH) and cytosol (c-MDH) isozymes of malate dehydrogenase (MDH: E.C. 1.1.1.37) were studied in the serum, liver and kidneys of rats at 2-week intervals using agar gel electrophoresis [15].

Associations of MDH2 with chemical compounds

• Inactivation of porcine heart mitochondrial malate dehydrogenase (L-malate: NAD+ oxidoreductase, EC 1.1.1.37) by selective modification of an active center histidine residue with the reagent iodoacetamide has been further investigated to examine the existence of and the enzymatic activity of a hybrid (half)-modified dimer [17].
• Biphasic inactivation of procine heart mitochondrial malate dehydrogenase by pyridoxal 5'-phosphate [18].
• Using [14C]citrate, the stoichiometry of citrate binding to mitochondrial malate dehydrogenase has been determined to be two equivalent sites per dimer, with a dissociation constant of 12.5 microM [19].
• Mitochondrial malate dehydrogenase assayed in the direction malate to oxalacetate is much less sensitive to palmitoyl-CoA, with Ki values of 50 muM at pH 10 and greater than 50 muM at pH 7 [20].
• 0. This reassociation at pH 7.5 is accompanied by a significant regain of enzymatic activity, indicating that NADH binding is able to partially overcome the negative effect of the cysteine modification on the pH-dependent subunit reassociation of mitochondrial malate dehydrogenase [21].

Other interactions of MDH2

• A model of the fusion protein with the cytosolic malate dehydrogenase shows no clear positive electrostatic potential surface between the two active sites, thus distinguishing it from the fusion protein with the mitochondrial malate dehydrogenase [12].
• Mitochondrial malate dehydrogenase and the cytoplasmic aspartate aminotransferase may conveniently be recovered from side fractions [22].

Analytical, diagnostic and therapeutic context of MDH2

• Cloning and sequence analysis of cDNAs encoding mammalian mitochondrial malate dehydrogenase [9].
• The immobilization of mitochondrial malate dehydrogenase on Sepharose beads and the demonstration of catalytically active subunits [23].
• The pH-dependent dissociation of porcine heart mitochondrial malate dehydrogenase (L-malate:NAD+ oxidoreductase, EC 1.1.1.37) has been further characterized using the technique of sedimentation velocity ultracentrifugation [24].
• The amino acid residues for substrate and cofactor binding identified by X-ray crystallography for pig heart cytoplasmic MDH are conserved in the 320 amino acid long mature higher-plant mMDH [25].
• Three potential salt bridges from Tf MDH were selected on the basis of their location in the protein (surface R176-D200, inter-subunit E57-K168 and intrasubunit R149-E275) and implemented on cMDH using site-directed mutagenesis [2].

References