Emodin O-methyltransferase from Aspergillus terreus.
Emodin O-methyltransferase, an enzyme catalyzing methylation of the 8-hydroxy group of emodin, was identified in the mould Aspergillus terreus IMI 16043, a (+)-geodin producing strain. The enzyme catalyzed the formation of questin from emodin and S-adenosyl-L-methionine. By chromatography on DEAE-cellulose, Phenyl Sepharose, Q-Sepharose, Hydroxyapatite, and CM-cellulose, emodin O-methyltransferase was purified to apparent homogeneity. The purified protein had a molecular weight of 322 kDa as estimated by gel filtration and 53.6 kDa as estimated by gel electrophoresis under denaturing conditions, suggesting that the active enzyme was a homohexamer. The enzyme showed pI 4.4 and optimum pH 7-8. Magnesium ion or manganese ion was not an absolute requirement, nor increased the enzyme activity. The enzyme had strict substrate specificity and very low Km values for both emodin (3.4 x 10(-7) M) and S-adenosyl-L-methionine (4.1 x 10(-6) M).
Chen
Z G
ZG
Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
Fujii
I
I
Ebizuka
Y
Y
Sankawa
U
U
D001230:Aspergillus / Q000201:enzymology*; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004642:Emodin / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007700:Kinetics; D008745:Methylation; D008780:Methyltransferases / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D008970:Molecular Weight; D013379:Substrate Specificity
D008780:Methyltransferases; C077861:emodin O-methyltransferase; D004642:Emodin