Le Bras G, Garel J R
J Biol Chem. 1985 Nov 5;260(25):13450-3.
N-terminal sequence analysis shows that the limited proteolysis of Escherichia coli phosphofructokinase results in the removal of the 40-50 C-terminal residues of each chain. When tetrameric, this proteolyzed derivative is still active albeit insensitive to allosteric effectors (Le Bras, G., and Garel, J.-R. (1982) Biochemistry 21, 6656-6660). In the absence of fructose 6-phosphate, the proteolyzed phosphofructokinase spontaneously loses its activity and dissociates into dimeric species. This inactivation/dissociation is slowed down by the binding of fructose 6-phosphate to only part of the sites; it is completely prevented by the saturation of all four fructose 6-phosphate sites. The other substrate ATP does not protect the proteolyzed phosphofructokinase against this inactivation/dissociation. This inactivation/dissociation is not due to denaturation and can be reversed in some conditions by the addition of fructose 6-phosphate. The active tetrameric structure of phosphofructokinase is stable when either the C-terminal segment is not removed or the fructose 6-phosphate sites are occupied.
N端序列分析表明，大肠杆菌磷酸果糖激酶的有限蛋白水解导致每条链的40 - 50个C端残基被去除。当形成四聚体时，这种经蛋白水解的衍生物仍然具有活性，尽管对变构效应物不敏感（勒布拉斯，G.，和加雷尔，J.-R.（1982年）《生物化学》21卷，6656 - 6660页）。在没有6-磷酸果糖的情况下，经蛋白水解的磷酸果糖激酶会自发失去活性并解离成二聚体形式。6-磷酸果糖仅与部分位点结合会减缓这种失活/解离过程；当所有四个6-磷酸果糖位点都被饱和时，该过程则完全被阻止。另一种底物ATP不能保护经蛋白水解的磷酸果糖激酶免于这种失活/解离。这种失活/解离并非由变性引起，并且在某些条件下通过添加6-磷酸果糖可以逆转。当C端片段未被去除或6-磷酸果糖位点被占据时，磷酸果糖激酶的活性四聚体结构是稳定的。
