Schulman M D, Valentino D, Nallin M, Kaplan L
Antimicrob Agents Chemother. 1986 Apr;29(4):620-4. doi: 10.1128/AAC.29.4.620.
The level of activity of avermectin B O-methyltransferase, the enzyme which catalyzes the conversion of avermectin B components to avermectin A components, was analyzed in a series of "Streptomyces avermitilis" mutants selected for increased production of the avermectins. In all of the mutants, increased avermectin production was accompanied by increased avermectin B O-methyltransferase activity. Both the average specific activity and the maximum observed specific activity of avermectin B O-methyltransferase increased in direct proportion to avermectin production. The level of avermectin B O-methyltransferase alone did not determine the extent of conversion of avermectin B components to avermectin A components, since a constant ratio of B components to A components was maintained throughout the fermentation even though avermectin B O-methyltransferase specific activity varied three- to fivefold. These results indicate that avermectin B O-methyltransferase is not rate limiting. The correlation between avermectin B O-methyltransferase specific activity and avermectin production is compatible with the hypothesis that genes coding for successive steps in the same secondary metabolite biosynthetic pathway are coordinately regulated.
在一系列为提高阿维菌素产量而筛选出的“阿维链霉菌”突变体中，分析了阿维菌素B O - 甲基转移酶（该酶催化阿维菌素B组分转化为阿维菌素A组分）的活性水平。在所有突变体中，阿维菌素产量的增加伴随着阿维菌素B O - 甲基转移酶活性的增加。阿维菌素B O - 甲基转移酶的平均比活性和观察到的最大比活性均与阿维菌素产量成正比增加。仅阿维菌素B O - 甲基转移酶的水平并不能决定阿维菌素B组分向阿维菌素A组分的转化程度，因为即使阿维菌素B O - 甲基转移酶的比活性变化了三到五倍，在整个发酵过程中B组分与A组分的比例仍保持恒定。这些结果表明阿维菌素B O - 甲基转移酶不是限速因素。阿维菌素B O - 甲基转移酶比活性与阿维菌素产量之间的相关性与以下假设相符：编码同一次生代谢物生物合成途径中连续步骤的基因受到协调调控。
