力复霉素前体甲基丙二酰CoA合成途径的研究

力复霉素合成的碳前体之一(2R)—甲基丙二酰CoA至少可以有三条酶学合成途径。三条途径中的关键酶分别为甲基丙二酰CoA转羧基酶、丙二酰CoA羧化酶、甲基丙二酰CoA变位酶和甲基丙二酰CoA消旋酶。通过比较各个酶活性的时间进程和力复霉素合成时间的相关性,以及各个酶的底物亲合力,对它们在地中海拟无枝酸菌(Amycolatopsis mediterranei)甲基丙二酰CoA合成中的贡献作了排序,发现甲基丙二酰CoA变位酶途径是主要负责酶系。但是各个途径的贡献排序并不是固定不变的,能受到环境因素的调控,丙酸盐的加入将抑制甲基丙二酰CoA变位酶活力,而使得甲基丙二酰CoA转羧基酶成为主要酶系。甲基丙二酰CoA合成途径的多样性有助于细胞对环境变化的灵活反应。此外,对各个酶的调控特性也进行了研究。

THE REGULATION OF METHYLMALONYL-CoA FORMATION PATHW AYS IN REFAMYCIN SV-PRODUCING AMYCOLATOPSIS MEDITERRANEl U32

( 2R)-Methylmalonyl-CoA, carbon precursor for rifamycin SV could be synthesized through at least three enzymatic systems from intermediates of TCA cycle and other pathways, they are methylmalonyl-CoA transcarboxylase, propionyl-CoA carboxylase, MCM and MCR. By comparing the time course of enzymatic activity with that of rifamycin synthesis and the Km values of the enzymes showed that MCM was the mainenzyme responsible for the methylmalonyl-CoA formation in A.mediterranei U32.The contribution of various systems was subject to regulation of environmental factors. The addition of propionate into medium makes the methylmalony-CoA transcarboxylase become the main enzyme responsible for the methylmalonyl-CoA formation.In addition, the regulatory characteristics of the key enzymes in various pathways were studied.