Coenzyme binding at different ionization states of cytoplasmic and mitochondrial malate dehydrogenase.
pH-titrations with NADH show two ionizable groups in mitochondrial and cytoplasmic malate dehydrogenase, the first with a pKa in the range 6.8-8.3 for the mitochondrial and 6.4-7.8 for the cytoplasmic enzyme, the second with a lower limit at 10.2 resp. 11. Comparison with bis-(dihydronicotinamide)-dinucleotide and dihydronicotinamide-ribosyl-P2-ribose-pyrophosphate instead of NADH indicates that the second alkaline ionization is caused by a residue placed near the adenine binding site of the active centre of the two isoenzymes. Binding studies with NADH and NAD+ give evidence for the participation of a group in the mitochondrial enzyme with pKa 6.8, deprotonation of which is necessary for detectable association of NAD+. In contrast the fixation of NAD+ to the cytoplasmic enzyme is independent of pH.
D000818:Animals; D003593:Cytoplasm / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D011485:Protein Binding
D009243:NAD; D008291:Malate Dehydrogenase