title: Molybdenum cofactor biosynthesis in Neurospora crassa: biochemical characterization of pleiotropic molybdoenzyme mutants nit-7, nit-8, nit-9A, B and C.
abstract: Available mutants of molybdenum cofactor (MoCo) biosynthesis of Neurospora crassa were studied for converting factor activity and for in vitro molybdate repair of nitrate reductase (NR) activity. Mutant nit-7 was found to contain an activity that fits the functional definition of converting factor activity in Escherichia coli. Its high molecular weight fraction converts a low molecular weight compound from nit-1 and nit-8 into biologically active molybdopterin (MPT). Like nit-1, mutant nit-8 is devoid of this activity. Mutants nit-9 A, B and C contain a protein-bound precursor form of MoCo, which is presumed to be MPT bound to apo-NR. It is converted into active MoCo as part of NR in the presence of reduced glutathione and high exogenous molybdate concentrations. The NR apoenzyme of nit-1 is needed to detect the total amount of MoCo after molybdate repair, because mutants nit-9 A, B and C build no detectable content of functional NR apoenzyme. Evidence is presented for the transfer of MPT from demolybdo-NR to free NR apoenzyme.
authors.affiliation: Institut für Chemische Pflanzenphysiologie, Universität Tübingen, Germany.
authors.forename: I S
authors.initials: IS
authors.lastname: Heck
authors.forename: H
authors.initials: H
authors.lastname: Ninnemann
mesh_terms: D003067:Coenzymes / Q000096:biosynthesis*; D004792:Enzyme Precursors / Q000378:metabolism; D008667:Metalloproteins / Q000378:metabolism*; D008982:Molybdenum / Q000378:metabolism*; D000090006:Molybdenum Cofactors; D009154:Mutation; D009492:Neurospora crassa / Q000235:genetics / Q000378:metabolism*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D011621:Pteridines / Q000378:metabolism*
chemical_list: D003067:Coenzymes; D004792:Enzyme Precursors; D008667:Metalloproteins; D008982:Molybdenum; D000090006:Molybdenum Cofactors; D050901:Nitrate Reductase; D009565:Nitrate Reductases; D011621:Pteridines; C044659:molybdate; C022261:molybdopterin