title: Propionate-3-nitronate oxidase from Penicillium atrovenetum is a flavoprotein which initiates the autoxidation of its substrate by O2.
abstract: On the fifth day following inoculation into an unstirred liquid surface culture, Penicillium atrovenetum abruptly, and reproducibly, secretes large quantities (2 g/liter) of the toxic antibiotic 3-nitropropionate into the medium. Concomitantly and with the same time course, crude extracts of the fungus acquire the ability to catalyze the oxidation of 3-nitropropionate by O2. We purified this activity some 300-fold to homogeneity and find it to be a soluble, dimeric (Mr = 73,000) flavoprotein oxidase having FMN as prosthetic group with lambda max = 363 and 433 nm. The preferred substrates are propionate-3-nitronate (3-NP-2) and O2 while the reaction products are malonate semialdehyde, NO2-, NO3-, O2-., and H2O2. Of 13 nitronates tested only butyrate-4-nitronate is more than 2% as reactive as 3-NP-2. 3-NP-2 (0.1 mM) rapidly reduces E-FMN anaerobically to E-FMNH., the flavin semiquinone (t1/2 less than 5 s), but reduces E-FMNH. to the fully reduced enzyme (E-FMNH2) very slowly (t1/2 approximately 900 s). The steady state turnover number with 0.1 mM 3-NP-2 and infinite O2 is 350 s-1. Therefore, the enzyme must oscillate almost exclusively between E-FMN and E-FMNH. during aerobic turnover. (Formula: see text). The complicated and non-integral reaction stoichiometry provides further support for this free radical mechanism. Each mole of 3-NP-. generated enzymatically initiates the nonenzymatic autoxidation of at least 2.2 mol of 3-NP-2 through a free radical chain reaction. An appropriate name for the newly characterized enzyme is propionate-3-nitronate oxidase.
authors: Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadephia 19104.
authors: D J
authors: DJ
authors: Porter
authors: H J
authors: HJ
authors: Bright
mesh_terms: D005486:Flavin Mononucleotide / Q000032:analysis; D005420:Flavoproteins / Q000302:isolation & purification; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D009574:Nitro Compounds; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000032:analysis / Q000302:isolation & purification*; D010100:Oxygen / Q000378:metabolism*; D010407:Penicillium / Q000201:enzymology; D011422:Propionates / Q000378:metabolism*
chemical_list: D005420:Flavoproteins; D005609:Free Radicals; D009574:Nitro Compounds; D011422:Propionates; D005486:Flavin Mononucleotide; D006861:Hydrogen Peroxide; D010088:Oxidoreductases; C053917:propionate-3-nitronate oxidase; C015392:3-nitropropionic acid; D010100:Oxygen