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• W1569607748 abstract "In the present work Psi-factor- producing oxygenases from Aspergillus nidulans, so called Ppo-enzymes have been studied and characterized. These enzymes are known to possess regulatory functions with respect to the fungal development and mycotoxin production. Bioinformatic analysis predicted two different heme domains for Ppo-enzymes: a fatty acid heme dioxygenase/peroxidase domain in the N-terminal region and a cytochrome-P450 domain in the C-terminal region. In order to study the biochemical properties of PpoA and PpoC, a heterologous E. coli expression system and a protein purification protocol have been established. While PpoA was purified to homogeneity in high amounts, PpoC appeared to be instable and lost its catalytic activity within a few minutes. PpoA was identified as a homotetrameric ferric heme protein that catalyzes the oxidation of mono- and polyunsaturated fatty acids. The presence of the thiolate ligated heme of the cytochrome-P450 domain was confirmed on the basis of sequence alignments, a characteristic heme-CO-spectrum and EPR-spectroscopy. Studies on the reaction mechanism showed that PpoA uses two different heme domains to catalyze two separate reactions. In a first reaction step linoleic acid is oxidized within the N-terminal fatty acid heme dioxygenase/peroxidase domain to (8R)-hydroperoxyoctadecadienoic acid. A tyrosyl-radical is formed during this reaction that abstracts an H-atom from C-8 of the fatty acid yielding a carbon-centered radical which in turn reacts with molecular dioxygen and the intermediate product (8R)-hydroperoxyoctadecadienoic acid is formed. In the second reaction step, 8-hydroperoxyoctadecadienoic acid is isomerized within the P450 heme thiolate domain to 5,8-dihydroxyoctadecadienoic acid. In contrast to PpoA PpoC harbors only the N-terminal fatty-acid-heme-dioxygenase/peroxidase domain and catalyzes mainly the dioxygenation of linoleic acid at the C-10 yielding 10-hydroperoxyoctadecadienoic acid and the corresponding hydroxyl-derivative. No isomerase activity was detected. Additionally, 10-HPODE was converted at low rates into 10-KODE (10-keto-octadecadienoic acid) and 10-HODE (10-hydroxyoctadecadienoic acid). In parallel, decomposition of 10-HPODE into 10-ODA (10-octadecynoic acid) and volatile C-8 alcohols that are, among other things, responsible for the characteristic mushroom flavor was observed. By using site-directed mutagenesis it was demonstrated that both enzymes share a similar mechanism for the oxidation of linoleic acid ; they both use a conserved tyrosine residue for catalysis and the directed oxygenation at the C-8 and C-10 is most likely controlled by a conserved amino acid residue in the dioxygenase domain that shields either the C-8 or C-10 of the fatty acid from molecular oxygen." @default.
• W1569607748 created "2016-06-24" @default.
• W1569607748 creator A5057507197 @default.
• W1569607748 date "2010-02-17" @default.
• W1569607748 modified "2023-09-27" @default.
• W1569607748 title "Biochemische Charakterisierung von PpoA aus Aspergillus nidulans" @default.
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