Chen Z G, Fujii I, Ebizuka Y, Sankawa U
Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
Arch Microbiol. 1992;158(1):29-34. doi: 10.1007/BF00249062.
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).
大黄素O-甲基转移酶是一种催化大黄素8-羟基甲基化的酶，在土曲霉IMI 16043（一种产生（+）-土菌素的菌株）中被鉴定出来。该酶催化大黄素和S-腺苷-L-甲硫氨酸生成 questin。通过在DEAE-纤维素、苯基琼脂糖、Q-琼脂糖、羟基磷灰石和CM-纤维素上进行色谱分离，大黄素O-甲基转移酶被纯化至表观均一性。通过凝胶过滤估计，纯化后的蛋白质分子量为322 kDa，在变性条件下通过凝胶电泳估计为53.6 kDa，这表明活性酶是一种同型六聚体。该酶的pI为4.4，最适pH为7 - 8。镁离子或锰离子不是绝对必需的，也不会增加酶活性。该酶对大黄素（3.4×10⁻⁷ M）和S-腺苷-L-甲硫氨酸（4.1×10⁻⁶ M）都具有严格的底物特异性和非常低的Km值。
