title: Purification and characterization of 40-kDa sterigmatocystin O-methyltransferase involved in aflatoxin biosynthesis.
abstract: Sterigmatocystin-O-methyltransferase (ST-OMTase), an enzyme catalyzing O-methylation of sterigmatocystin with S-adenosylmethionine (SAM), was purified to electrophoretic homogeneity by immunoaffinity chromatography. A novel spectrofluorometric method was established to quantitatively determine the enzymatic activity of ST-OMTase. The purified protein, with a molecular weight of 40 kDa by SDS-PAGE, was sensitive to thiol reagents and low concentrations of heavy metal ions. Using a nutritional shift assay, the expression patterns for ST-OMTase and the transcripts of its corresponding gene, omtA, correlated well with that for aflatoxin B(1) formation. Neither methyltransferase activity nor omtA, mRNA was detected in the fungal cultures of nonaflatoxigenic isolates, including A. flavus, A. sojae, A. nidulans and A. versicolor under optimal growing conditions for aflatoxin B(1) production.
authors.affiliation: Department of Food Microbiology and Toxicology and Food Research Institute, and Environmental Toxicology Center, University of Wisconsin-Madison, WI 53706 USA.
authors.forename: B H
authors.initials: BH
authors.lastname: Liu
authors.forename: D
authors.initials: D
authors.lastname: Bhatnagar
authors.forename: F S
authors.initials: FS
authors.lastname: Chu
mesh_terms: D000348:Aflatoxins / Q000096:biosynthesis*; D005656:Fungal Proteins; D007700:Kinetics; D008780:Methyltransferases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D008970:Molecular Weight; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D000348:Aflatoxins; D005656:Fungal Proteins; D012333:RNA, Messenger; D008780:Methyltransferases; C096006:omtA protein, Aspergillus