Vallari D S, Jackowski S, Rock C O
J Biol Chem. 1987 Feb 25;262(6):2468-71.
Pantothenate kinase catalyzes the rate-controlling step in the coenzyme A (CoA) biosynthetic pathway, and its activity is modulated by the size of the CoA pool. The effect of nonesterified CoA (CoASH) and CoA thioesters on the activity of pantothenate kinase was examined to determine which component of the CoA pool is the most effective regulator of the enzyme from Escherichia coli. CoASH was five times more potent than acetyl-CoA or other CoA thioesters as an inhibitor of pantothenate kinase activity in vitro. Inhibition by CoA thioesters was not due to their hydrolysis to CoASH. CoASH inhibition was competitive with respect to ATP, thus providing a mechanism to coordinate CoA production with the energy state of the cell. There were considerable differences in the size and composition of the CoA pool in cells grown on different carbon sources, and a carbon source shift experiment was used to test the inhibitory effect of the different CoA species in vivo. A shift from glucose to acetate as the carbon source resulted in an increase in the CoASH:acetyl-CoA ratio from 0.7 to 4.3. The alteration in the CoA pool composition was associated with the selective inhibition of pantothenate phosphorylation, consistent with CoASH being a more potent regulator of pantothenate kinase activity in vivo. These results demonstrate that CoA biosynthesis is regulated through feedback inhibition of pantothenate kinase primarily by the concentration of CoASH and secondarily by the size of the CoA thioester pool.
泛酸激酶催化辅酶A（CoA）生物合成途径中的限速步骤，其活性受CoA库大小的调节。研究了游离CoA（CoASH）和CoA硫酯对泛酸激酶活性的影响，以确定CoA库的哪个组分是大肠杆菌中该酶最有效的调节剂。在体外，CoASH作为泛酸激酶活性的抑制剂，其效力是乙酰CoA或其他CoA硫酯的五倍。CoA硫酯的抑制作用并非因其水解为CoASH所致。CoASH的抑制作用对ATP具有竞争性，从而提供了一种将CoA产生与细胞能量状态相协调的机制。在以不同碳源生长的细胞中，CoA库的大小和组成存在显著差异，利用碳源转换实验来测试不同CoA种类在体内的抑制作用。将碳源从葡萄糖转换为乙酸盐会导致CoASH:乙酰CoA的比例从0.7增加到4.3。CoA库组成的改变与泛酸磷酸化的选择性抑制相关，这与CoASH在体内是泛酸激酶活性更有效的调节剂一致。这些结果表明，CoA生物合成主要通过CoASH的浓度以及其次通过CoA硫酯库的大小对泛酸激酶的反馈抑制来进行调节。
