title: Purification and characterization of malate dehydrogenase from Cryptococcus neoformans.
abstract: The NAD-dependent malate dehydrogenase (EC 1.1.1.37) was purified from Cryptococcus neoformans, a basidiomycetious yeast that is an opportunistic pathogen of AIDS patients. The purified enzyme was a dimer of 35 kDa subunits that exhibited uncompetitive substrate inhibition by oxalacetate, typical for mitochondrial malate dehydrogenases from other sources. Product inhibition studies indicated an ordered sequential kinetic mechanism, with pyridine dinucleotide being the substrate that binds to the free enzyme form. Unique aspects of this malate dehydrogenase were inhibition by zinc ion, competitive versus malate with Ki of 30 microM, and inhibition by heparin. Heparin inhibition was competitive versus either NAD or malate, with Ki of 0.35 microM. Heparin molecules of nominal molecular weight of 30,000 or 3000 were equally effective inhibitors. A model is presented to explain the high affinity of the enzyme for heparin.
authors.affiliation: Department of Biochemistry and Anaerobic Microbiology, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
authors.forename: Y A
authors.initials: YA
authors.lastname: Mahmoud
authors.forename: S M
authors.initials: SM
authors.lastname: el Souod
authors.forename: W G
authors.initials: WG
authors.lastname: Niehaus
mesh_terms: D017088:AIDS-Related Opportunistic Infections / Q000188:drug therapy / Q000382:microbiology; D001665:Binding Sites; D003453:Cryptococcosis / Q000150:complications / Q000188:drug therapy / Q000382:microbiology; D003455:Cryptococcus neoformans / Q000201:enzymology* / Q000472:pathogenicity; D004352:Drug Resistance, Microbial; D006493:Heparin / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008291:Malate Dehydrogenase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000302:isolation & purification*; D008970:Molecular Weight; D009243:NAD / Q000494:pharmacology; D010071:Oxaloacetates / Q000494:pharmacology; D011487:Protein Conformation
chemical_list: D010071:Oxaloacetates; D009243:NAD; D006493:Heparin; D008291:Malate Dehydrogenase