Masurekar P S, Demain A L
Appl Microbiol. 1974 Aug;28(2):265-70. doi: 10.1128/am.28.2.265-270.1974.
We previously reported that lysine inhibits in vivo homocitrate synthesis in the lysine bradytroph, Penicillium chrysogenum L(1), and that such feedback inhibition could explain the known lysine inhibition of penicillin formation. In the present study, it was found that dialyzed cell-free extracts of mutant L(1) converted [1-(14)C]acetate to homocitrate. This homocitrate synthase activity was extremely labile but could be stabilized by high salt concentrations. The pH optimum of the reaction was 6.9, and the K(m) was 5.5 mM with respect to alpha-ketoglutarate. The reaction was also dependent upon the presence of Mg(2+), adenosine 5'-triphosphate, and coenzyme A. Surprisingly, the activity in these crude extracts was not inhibited by lysine. Benzylpenicillin at a high concentration (20 mM) partially inhibited the enzyme, an effect that was enhanced by lysine. Casein hydrolysate also partially inhibited the enzyme.
我们之前报道过，赖氨酸可抑制迟缓型赖氨酸营养缺陷型产黄青霉L(1)体内高柠檬酸的合成，且这种反馈抑制可以解释已知的赖氨酸对青霉素合成的抑制作用。在本研究中，发现突变体L(1)的透析无细胞提取物可将[1-(14)C]乙酸盐转化为高柠檬酸。这种高柠檬酸合酶活性极不稳定，但可通过高盐浓度使其稳定。该反应的最适pH为6.9，相对于α-酮戊二酸的K(m)为5.5 mM。该反应还依赖于Mg(2+)、腺苷5'-三磷酸和辅酶A的存在。令人惊讶的是，这些粗提取物中的活性不受赖氨酸的抑制。高浓度（20 mM）的苄青霉素可部分抑制该酶，赖氨酸可增强这种抑制作用。酪蛋白水解物也可部分抑制该酶。
