Muth W L, Nash C H
Antimicrob Agents Chemother. 1975 Sep;8(3):321-7. doi: 10.1128/AAC.8.3.321.
The final step in the biosynthesis of mycophenolic acid involves the transfer of a methyl group from S-adenosylmethionine to demethylmycophenolic acid. The enzyme, S-adenosylmethionine:demethylmycophenolic acid O-methyltransferase, was isolated from Penicillium stoloniferum and purified 2,700-fold by ammonium sulfate fractionation and diethylaminoethyl-cellulose and Sephadex G-200 chromatography. Maximum enzyme activity was achieved at pH 7.5 and a temperature of 27 to 28 C. The apparent K(m) for demethylmycophenolic acid was 3.1 x 10(-6) M. The enzyme preparation was 50% inactivated when exposed to 33 C for 15 min. Mycophenolic acid, homocystine, S-adenosyl-homocysteine, ethanol, and Mg(2+) inhibited the methyltransferase. This enzyme appears to be subject to end product inhibition which may regulate the synthesis of mycophenolic acid. The methyltransferase activity was highest during the early phases of the fermentation.
霉酚酸生物合成的最后一步涉及将甲基从S-腺苷甲硫氨酸转移至去甲基霉酚酸。S-腺苷甲硫氨酸：去甲基霉酚酸O-甲基转移酶从匐枝青霉中分离出来，并通过硫酸铵分级分离、二乙氨基乙基纤维素和葡聚糖G-200柱层析进行了2700倍的纯化。酶的最大活性在pH 7.5以及27至28℃的温度下实现。去甲基霉酚酸的表观米氏常数（K(m)）为3.1×10⁻⁶ M。当在33℃下暴露15分钟时，酶制剂有50%失活。霉酚酸、高胱氨酸、S-腺苷高半胱氨酸、乙醇和Mg²⁺抑制甲基转移酶。这种酶似乎受到终产物抑制，这可能调节霉酚酸的合成。甲基转移酶活性在发酵早期阶段最高。
