Cumme G A, Bublitz R, Horn A
Eur J Biochem. 1981 Mar 16;115(1):59-65.
It is known from theoretical work that very simple enzyme systems may exhibit non-linear dynamic properties like those found in vivo. To realize such a system experimentally, an ATP-producing reaction (pyruvate kinase) was coupled with an ATP-consuming reaction (phosphofructokinase). The substrate-stat technique has been adapted to characterize each single enzyme as well as to follow up one enzyme in the coupled system. If the plots of both pyruvate kinase activity versus [ADP] and phosphofructokinase activity versus [ATP] are hyperbolic, the coupled system approaches a unique steady state as predicted from the single characteristics. Under assay conditions where phosphofructokinase is inhibited by ATP, its characteristics as found in a single assay and in the coupled system are different. For a system with ATP-inhibited phosphofructokinase, a paradoxical behaviour is predicted and is demonstrated experimentally. If the total pyruvate kinase activity is increased over a certain limit, the system is switched from a low [ATP], high-activity steady state into a high [ATP] low-activity steady state.
从理论研究可知，非常简单的酶系统可能表现出类似于体内发现的非线性动力学特性。为了通过实验实现这样一个系统，将一个产生ATP的反应（丙酮酸激酶）与一个消耗ATP的反应（磷酸果糖激酶）偶联起来。底物恒态技术已被用于表征每种单一酶以及追踪偶联系统中的一种酶。如果丙酮酸激酶活性对[ADP]的曲线以及磷酸果糖激酶活性对[ATP]的曲线都是双曲线，那么偶联系统会如从单一特性所预测的那样趋近于一个独特的稳态。在磷酸果糖激酶被ATP抑制的测定条件下，其在单一测定和偶联系统中所呈现的特性是不同的。对于一个磷酸果糖激酶被ATP抑制的系统，预测并通过实验证明了一种矛盾行为。如果丙酮酸激酶的总活性增加超过一定限度，系统会从一个低[ATP]、高活性的稳态转变为一个高[ATP]、低活性的稳态。
