title: Characterization of malate dehydrogenase from the hyperthermophilic archaeon Pyrobaculum islandicum.
abstract: Native and recombinant malate dehydrogenase (MDH) was characterized from the hyperthermophilic, facultatively autotrophic archaeon Pyrobaculum islandicum. The enzyme is a homotetramer with a subunit mass of 33 kDa. The activity kinetics of the native and recombinant proteins are the same. The apparent K ( m ) values of the recombinant protein for oxaloacetate (OAA) and NADH (at 80 degrees C and pH 8.0) were 15 and 86 microM, respectively, with specific activity as high as 470 U mg(-1). Activity decreased more than 90% when NADPH was used. The catalytic efficiency of OAA reduction by P. islandicum MDH using NADH was significantly higher than that reported for any other archaeal MDH. Unlike other archaeal MDHs, specific activity of the P. islandicum MDH back-reaction also decreased more than 90% when malate and NAD(+) were used as substrates and was not detected with NADP(+). A phylogenetic tree of 31 archaeal MDHs shows that they fall into 5 distinct groups separated largely along taxonomic lines suggesting minimal lateral mdh transfer between Archaea.
authors.affiliation: Department of Microbiology, University of Massachusetts, N203 Morrill Science Center IV North, Amherst, MA 01003, USA.
authors.forename: Lynda J
authors.initials: LJ
authors.lastname: Yennaco
authors.forename: Yajing
authors.initials: Y
authors.lastname: Hu
authors.forename: James F
authors.initials: JF
authors.lastname: Holden
mesh_terms: D002952:Citric Acid Cycle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008291:Malate Dehydrogenase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D008970:Molecular Weight; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D062907:Oxaloacetic Acid / Q000378:metabolism; D010802:Phylogeny; D011487:Protein Conformation; D021122:Protein Subunits; D041543:Pyrobaculum / Q000201:enzymology* / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D020539:Sequence Analysis, Protein; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D008293:Malates; D021122:Protein Subunits; D011994:Recombinant Proteins; D009243:NAD; D062907:Oxaloacetic Acid; D009249:NADP; C030298:malic acid; D008291:Malate Dehydrogenase