title: Inactivation of porcine heart cytoplasmic malate dehydrogenase by pyridoxal 5'-phosphate.
abstract: Pyridoxal 5'-phosphate (pyridoxal-5'-P) has been found to act as a bifunctional reagent during the inactivation of porcine heart cytoplasmic malate dehydrogenase (L-malate: NAD+ oxidoreductase, EC 1.1.1.37). The biphasic kinetics and X-azolidine-like structure formed were similar to those observed for mitochondrial malate dehydrogenase (Wimmer, M.J., Mo, T., Sawyers, D.L., and Harrison, J.H. (1975) J. Biol. Chem. 250, 710-715). In the cytoplasmic enzyme, however, irreversible inactivation representing X-azolidine formation was found to be the dominant characteristic of the interaction with pyridoxal-5'-P. Spectral evidence indicated that at total inactivation 2 mol of pyridoxal-5'-P were incorporated per mol of enzyme or one pyridoxal-5'-P per enzymatic active site. The presence of NADH protected the enzyme from inactivation suggesting interaction of pyridoxal-5'-P at or near the enzymatic active centers of this enzyme. Fluorometric titrations indicated that pyridoxal-5'-P-inactivated enzyme failed to bind NADH or at least failed to bind NADH in the same fashion as native enzyme.
mesh_terms: D003593:Cytoplasm / Q000201:enzymology; D007700:Kinetics; D008291:Malate Dehydrogenase / Q000037:antagonists & inhibitors*; D009206:Myocardium / Q000201:enzymology*; D009243:NAD / Q000494:pharmacology; D010071:Oxaloacetates / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence
chemical_list: D010071:Oxaloacetates; D009243:NAD; D011732:Pyridoxal Phosphate; D008291:Malate Dehydrogenase