Details

Autor(en) / Beteiligte

• Troncoso, Claudia
• Cárcamo, José
• Hedden, Peter
• Tudzynski, Bettina
• Cecilia Rojas, M.

Titel

Influence of electron transport proteins on the reactions catalyzed by Fusarium fujikuroi gibberellin monooxygenases

Ist Teil von

• Phytochemistry (Oxford), 2008-02, Vol.69 (3), p.672-683

Ort / Verlag

Amsterdam: Elsevier Ltd

Erscheinungsjahr

2008

Quelle

MEDLINE

Beschreibungen/Notizen

• Products formed by GA 14 synthase and gibberellin 20-oxidase in Fusarium fujikuroi mutants that lack cytochrome P450 reductase (CPR) are qualitatively and quantitatively different from those produced in CPR-containing strains. Interaction of these P450s with cyt b5:cyt b5 reductase in the mutants would account for the differences found. The multifunctional cytochrome P450 monooxygenases P450-1 and P450-2 from Fusarium fujikuroi catalyze the formation of GA 14 and GA 4, respectively, in the gibberellin (GA)-biosynthetic pathway. However, the activity of these enzymes is qualitatively and quantitatively different in mutants lacking the NADPH:cytochrome P450 oxidoreductase (CPR) compared to CPR-containing strains. 3β-Hydroxylation, a major P450-1 activity in wild-type strains, was strongly decreased in the mutants relative to oxidation at C-6 and C-7, while synthesis of C 19-GAs as a result of oxidative cleavage of C-20 by P450-2 was almost absent whereas the C-20 alcohol, aldehyde and carboxylic acid derivatives accumulated. Interaction of the monooxygenases with alternative electron transport proteins could account for these different product distributions. In the absence of CPR, P450-1 activities were NADH-dependent, and stimulated by cytochrome b5 or by added FAD. These properties as well as the decreased efficiency of P450-1 and P450-2 in the mutants are consistent with the participation of cytochrome b5:NADH cytochrome b5 reductase as redox partner of the gibberellin monooxygenases in the absence of CPR. We provide evidence, from either incubations of GA 12 (C-20 methyl) with cultures of the mutant suspended in [ 18O]H 2O or maintained under an atmosphere of [ 18O]O 2:N 2 (20:80), that GA 15 (C-20 alcohol) and GA 24 (C-20 aldehyde) are formed directly from dioxygen and not from hydrolysis of covalently enzyme-bound intermediates. Thus these partially oxidized GAs correspond to intermediates of the sequential oxidation of C-20 catalyzed by P450-2.