title: Purification and properties of NADP-dependent formate dehydrogenase from Clostridium thermoaceticum, a tungsten-selenium-iron protein.
abstract: NADP-dependent formate dehydrogenase (NADP+) (EC 1.2.1.43) from Clostridium thermoaceticum has been purified to a specific activity of about 1100 mumol min-1 mg-1 when assayed at 55 degrees C and pH 7.5. The enzyme is extremely oxygen-sensitive and 7.6 microM of O2 causes 50% inhibition of initial velocity under assay conditions. Purification was done in an atmosphere at 95% N2 and 5% H2 and by including azide, dithionite, and glycerol as stabilizing agents in all buffer solutions. The enzyme contains, in molar ratios, 2 tungsten, 2 selenium, 36 iron, and about 50 inorganic sulfur. It has a molecular weight of about 340,000 and consist of two each of two different subunits giving the composition alpha 2 beta 2. The molecular weight of the alpha-subunit is 96,000 and that of the beta-subunit is 76,000. The selenium resides in the two alpha-subunits. Tungsten is released from the protein on denaturation and may exist as a tungsten cofactor. The enzyme catalyzes a reduction of CO2 with NADPH at pH 7.5 and 55 degrees C and Keq at these conditions is (2.35 +/- 0.49) x 10(-2) if CO2 is considered the active species and (1.48 +/- 0.31) x 10(-3) if HCO3- is the active species.
mesh_terms: D000332:Aerobiosis; D000445:Aldehyde Oxidoreductases / Q000302:isolation & purification* / Q000378:metabolism; D003013:Clostridium / Q000201:enzymology*; D005560:Formate Dehydrogenases; D007501:Iron / Q000032:analysis; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D012643:Selenium / Q000032:analysis; D014414:Tungsten / Q000032:analysis
chemical_list: D046911:Macromolecular Substances; D007501:Iron; C037212:formate dehydrogenase (NADP+); D005560:Formate Dehydrogenases; D000445:Aldehyde Oxidoreductases; D012643:Selenium; D014414:Tungsten