Role of oxygenases in pisatin biosynthesis and in the fungal degradation of maackiain
Some isolates of the plant pathogen Nectria haematococca detoxify the isoflavonoid phytoalexin (-)maackiain by hydroxylation at carbon 6a. Precursor feeding studies strongly suggest that the penultimate step in (+)pisatin biosynthesis by Pisum sativum is 6a-hydroxylation of (+)maackiain. They have used /sup 18/O labeling to test the involvement of oxygenases in these two reactions. When fungal metabolism of maackiain took place under /sup 18/O/sub 2/, the product was labeled with 99% efficiency; no label was incorporated by metabolism in H/sub 2//sup 18/O. Pisatin synthesized by pea pods in the presence of /sup 18/O/sub 2/ or H/sub 2//sup 18/O was a mixture of molecules containing up to three labeled oxygen atoms. Primary mass spectra of such mixtures were complex but were greatly simplified by tandem MS. This analysis indicated that the 6a oxygen of pisatin was derived from H/sub 2/O and not from O/sub 2/. Labeling patterns for the other five oxygen atoms were consistent with the proposed pathway for biosynthesis of pisatin and related isoflavonoids. They conclude that the fungal hydroxylation of maackiain is catalyzed by an oxygenase, but the biosynthetic route to the 6a hydroxyl of pisatin is unknown.
- Research Organization:
- Cornell Univ., Ithaca, NY (United States)
- DOE Contract Number:
- AC02-83ER13073
- OSTI ID:
- 6526008
- Journal Information:
- Plant Physiol.; (United States), Vol. 83:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
OXYGENASES
BIOCHEMICAL REACTION KINETICS
PIGMENTS
DETOXIFICATION
BIOLOGICAL PATHWAYS
BIOSYNTHESIS
FUNGI
OXYGEN 18
PATHOGENS
PISUM
TRACER TECHNIQUES
BACTERIA
ENZYMES
EVEN-EVEN NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LEGUMINOSAE
LIGHT NUCLEI
MICROORGANISMS
NUCLEI
OXIDOREDUCTASES
OXYGEN ISOTOPES
PLANTS
REACTION KINETICS
RHIZOBIUM
STABLE ISOTOPES
SYNTHESIS
550201* - Biochemistry- Tracer Techniques