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Conversion of 11-hydroxy-O-methylsterigmatocystin to aflatoxin G1 in Aspergillus parasiticus.

Applied microbiology and biotechnology (2010-12-15)
Hongmei Zeng, Hidemi Hatabayashi, Hiroyuki Nakagawa, Jingjing Cai, Ryoya Suzuki, Emi Sakuno, Toshitsugu Tanaka, Yasuhiro Ito, Kenneth C Ehrlich, Hiromitsu Nakajima, Kimiko Yabe
RÉSUMÉ

In aflatoxin biosynthesis, aflatoxins G(1) (AFG(1)) and B(1) (AFB(1)) are independently produced from a common precursor, O-methylsterigmatocystin (OMST). Recently, 11-hydroxy-O-methylsterigmatocystin (HOMST) was suggested to be a later precursor involved in the conversion of OMST to AFB(1), and conversion of HOMST to AFB(1) was catalyzed by OrdA enzyme. However, the involvement of HOMST in AFG(1) formation has not been determined. In this work, HOMST was prepared by incubating OrdA-expressing yeast with OMST. Feeding Aspergillus parasiticus with HOMST allowed production of AFG(1) as well as AFB(1). In cell-free systems, HOMST was converted to AFG(1) when the microsomal fraction, the cytosolic fraction from A. parasiticus, and yeast expressing A. parasiticus OrdA were added. These results demonstrated (1) HOMST is produced from OMST by OrdA, (2) HOMST is a precursor of AFG(1) as well as AFB(1), and (3) three enzymes, OrdA, CypA, and NadA, and possibly other unknown enzymes are involved in conversion of HOMST to AFG(1).

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Sigma-Aldrich
Aflatoxin G1, from Aspergillus flavus
Supelco
Aflatoxine G1 solution, 2 μg/mL in acetonitrile, analytical standard
Aflatoxine G1 solution, 3.78 μg/g in acetonitrile, ERM®, certified reference material
Supelco
Aflatoxin G1