Choate G L, Lan L, Mansour T E
J Biol Chem. 1985 Apr 25;260(8):4815-22.
6-Phosphofructo-1-kinase (phosphofructokinase) (ATP:D-fructose-6-P 1-phosphotransferase, EC 2.7.1.11) can be identified in sheep heart homogenates in two forms, a soluble form and a form bound to the particulate fraction. Homogenates from immediately-dissected hearts have the enzyme in the soluble form, while those collected after a delay have the enzyme bound to the particulate fraction. Aldolase appears to show the same change in its location. Homogenization in a solution with concentrated macromolecular species (20% albumin) results in a greater association of phosphofructokinase and of aldolase to the particulate fraction in homogenates from immediately dissected hearts. Phosphofructokinase activity can be solubilized by two specific means: by high ionic strength, which is dependent upon specific salts; or by low ionic strength, which is dependent upon the presence of phosphofructokinase substrates or modifier ligands. These two means of solubilization are affected differently upon decreasing the pH below 6.9: the solubilization at low ionic strength is prevented, whereas phosphofructokinase is still solubilized by high ionic strength. Under the latter condition, the enzyme is in the inactive dimeric state, which can be activated at an alkaline pH. Myofibrils present in the particulate fraction can account for the binding of phosphofructokinase in heart homogenates. Purified myofibrils, when added to heart supernatant fluids, can bind phosphofructokinase at a slightly acidic pH. Conditions for phosphofructokinase binding to myofibrils, as well as its dissociation, follow what was observed with the binding of phosphofructokinase to the particulate fraction. At an acidic pH, and in the presence of a high concentration of ATP, phosphofructokinase exhibits low activity. However, if phosphofructokinase is assayed under these conditions while bound to myofibrils, the enzyme is activated.
6-磷酸果糖-1-激酶（磷酸果糖激酶）（ATP：D-果糖-6-磷酸1-磷酸转移酶，EC 2.7.1.11）在绵羊心脏匀浆中可被鉴定为两种形式，一种是可溶形式，另一种是与颗粒部分结合的形式。刚解剖的心脏匀浆中的酶为可溶形式，而延迟采集的心脏匀浆中的酶则与颗粒部分结合。醛缩酶似乎在其位置上也有相同的变化。在含有高浓度大分子物质（20%白蛋白）的溶液中匀浆，会导致刚解剖的心脏匀浆中磷酸果糖激酶和醛缩酶与颗粒部分的结合增加。磷酸果糖激酶的活性可以通过两种特定方法溶解：通过高离子强度，这取决于特定的盐；或通过低离子强度，这取决于磷酸果糖激酶底物或修饰配体的存在。当pH值降至6.9以下时，这两种溶解方法受到的影响不同：低离子强度下的溶解被阻止，而磷酸果糖激酶仍可通过高离子强度溶解。在后一种情况下，酶处于无活性的二聚体状态，可在碱性pH值下被激活。颗粒部分中存在的肌原纤维可以解释心脏匀浆中磷酸果糖激酶的结合。纯化的肌原纤维添加到心脏上清液中时，在略酸性pH值下可结合磷酸果糖激酶。磷酸果糖激酶与肌原纤维结合及其解离的条件，与磷酸果糖激酶与颗粒部分结合时观察到的情况一致。在酸性pH值和高浓度ATP存在的情况下，磷酸果糖激酶活性较低。然而，如果在这些条件下结合肌原纤维时测定磷酸果糖激酶，该酶会被激活。
