Kane J F, Homes W M, Smiley K L, Jensen R A
J Bacteriol. 1973 Jan;113(1):224-32. doi: 10.1128/jb.113.1.224-232.1973.
The anthranilate synthase aggregate from Bacillus subtilis is composed of two nonidentical subunits, denoted E and X, which are readily associated or dissociated. A complex of subunit E and X can utilize glutamine or ammonia as substrates in the formation of anthranilate. Partially purified subunit E is capable of using only ammonia as the amide donor in the anthranilate synthase reaction. The stability of the EX complex is strongly influenced by glutamine and by the concentrations of the subunits. Glutamine stabilizes the aggregate as a molecular species in which the velocity of the glutamine-reactive anthranilate synthase is a linear function of protein concentration. In the absence of glutamine the aggregate is readily dissociated following dilution of the extract; that is, velocity concaves upward as a function of increasing protein concentration. Reassociation of the EX complex is characterized by a velocity lag (or hysteretic response) before steady-state velocity for the glutamine-reactive anthranilate synthase is reached. We propose that association and dissociation of the anthranilate synthase aggregate may be physiologically significant and provide a control mechanism whereby repression or derepression causes disproportionate losses or gains in activity by virtue of protein-protein interactions between subunits E and X.
来自枯草芽孢杆菌的邻氨基苯甲酸合酶聚集体由两个不同的亚基组成，分别称为E和X，它们很容易结合或解离。亚基E和X的复合物在邻氨基苯甲酸的形成过程中可以利用谷氨酰胺或氨作为底物。部分纯化的亚基E在邻氨基苯甲酸合酶反应中仅能使用氨作为酰胺供体。EX复合物的稳定性受到谷氨酰胺和亚基浓度的强烈影响。谷氨酰胺将聚集体稳定为一种分子形式，其中谷氨酰胺反应性邻氨基苯甲酸合酶的速度是蛋白质浓度的线性函数。在没有谷氨酰胺的情况下，提取物稀释后聚集体很容易解离；也就是说，速度随着蛋白质浓度的增加而向上凹。EX复合物的重新结合的特征是在达到谷氨酰胺反应性邻氨基苯甲酸合酶的稳态速度之前存在速度滞后（或滞后响应）。我们提出，邻氨基苯甲酸合酶聚集体的结合和解离可能具有生理意义，并提供一种控制机制，通过这种机制，抑制或去抑制由于亚基E和X之间的蛋白质-蛋白质相互作用而导致活性不成比例地损失或增加。
