Kamemoto E S, Mansour T E
J Biol Chem. 1986 Mar 25;261(9):4346-51.
Phosphofructokinase from the liver fluke Fasciola hepatica was purified from extracts of the whole organisms. The molecular weight of the protomer as determined by sodium dodecyl sulfate-gel electrophoresis is 83,000. Phosphorylation of the liver fluke phosphofructokinase by the catalytic subunit of cAMP-dependent protein kinase occurred at a rate that was at least an order of magnitude greater than that observed with mammalian heart phosphofructokinase. The maximum level of phosphate incorporated was 0.22 mol P/mol of protomer. The kinetic properties of the enzyme were greatly altered as a result of phosphorylation. Compared to native enzyme, phosphorylated enzyme had a greater affinity for its substrate Fru-6-P and a decreased sensitivity to inhibition by ATP. These kinetic changes were similar to those of native enzyme in the presence of positive modifiers such as AMP. AMP also activated the phosphorylated enzyme. Activation of the phosphorylated enzyme by AMP was characterized by a further increase in affinity for Fru-6-P and a further decrease in sensitivity to ATP inhibition. Thus, the liver fluke phosphofructokinase can be modulated by covalent phosphorylation as well as noncovalent binding of different modifier ligands.
从肝片吸虫（Fasciola hepatica）的全生物体提取物中纯化得到了磷酸果糖激酶。通过十二烷基硫酸钠 - 凝胶电泳测定，该单体的分子量为83,000。环磷酸腺苷（cAMP）依赖性蛋白激酶的催化亚基对肝片吸虫磷酸果糖激酶的磷酸化速率至少比在哺乳动物心脏磷酸果糖激酶中观察到的速率高一个数量级。掺入的磷酸盐的最大水平为0.22摩尔磷/摩尔单体。由于磷酸化，该酶的动力学性质发生了很大变化。与天然酶相比，磷酸化酶对其底物果糖 - 6 - 磷酸（Fru - 6 - P）具有更高的亲和力，并且对ATP抑制的敏感性降低。这些动力学变化与在存在正性调节剂如AMP时天然酶的变化相似。AMP也激活了磷酸化酶。AMP对磷酸化酶的激活表现为对Fru - 6 - P的亲和力进一步增加，对ATP抑制的敏感性进一步降低。因此，肝片吸虫磷酸果糖激酶可以通过共价磷酸化以及不同调节剂配体的非共价结合来调节。
