Department of Chemistry and Biochemistry, California State University, Los Angeles, California 90032.
Plant Physiol. 1989 Nov;91(3):954-60. doi: 10.1104/pp.91.3.954.
The hysteretic behavior of phosphoenolpyruvate (PEP) carboxylase from Crassula argentea has been investigated. Incubation of the purified enzyme with the inhibitor malate prior to starting the reaction by the addition of PEP resulted in a kinetic lag of several minutes duration. The length of the lag was inversely proportional to the enzyme concentration, suggesting subunit association-dissociation as the hysteretic mechanism, rather than a mechanism based on a slow conformational change in the enzyme. Dynamic laser light scattering measurements also support this conclusion, showing that the diffusion coefficient of malate-incubated enzyme slowly decreased after the reaction was started by the addition of PEP. Lags were observed only at pH values of 7.5 or lower. Maximum lags were observed after 10 min of preincubation with malate. Fumarate and succinate, which like malate caused mixed inhibition, also caused lags. In contrast, no lag was induced by malate in the presence of PEP or by the competitive inhibitor phosphoglycolate. The activators glucose 6-phosphate and malonate decreased the malate-induced lag.
已研究了来自马齿苋属植物的磷酸烯醇丙酮酸（PEP）羧化酶的滞后行为。在通过添加 PEP 开始反应之前，将纯化的酶与抑制剂苹果酸一起孵育会导致数分钟的动力学滞后。滞后的长度与酶浓度成反比，表明亚基缔合-解离是滞后机制，而不是基于酶中缓慢构象变化的机制。动态激光散射测量也支持这一结论，表明在通过添加 PEP 开始反应后，苹果酸孵育的酶的扩散系数缓慢降低。仅在 pH 值为 7.5 或更低时观察到滞后。在用苹果酸预孵育 10 分钟后观察到最大滞后。富马酸和琥珀酸，如苹果酸一样引起混合抑制，也引起滞后。相比之下，在 PEP 存在下或在竞争性抑制剂磷酸甘油酸存在下，苹果酸不会引起滞后。激活剂葡萄糖 6-磷酸和丙二酸降低了苹果酸诱导的滞后。
