Ascenzi P, Amiconi G, Bolognesi M, Menegatti E, Guarneri M
Biochim Biophys Acta. 1985 Dec 20;832(3):378-82. doi: 10.1016/0167-4838(85)90274-2.
The effect of Ile-Val concentration (up to 2.0 M) on the thermodynamic parameters for the binding of the porcine pancreatic secretory trypsin inhibitor (Kazal inhibitor) to trypsinogen has been investigated at pH 5.5 between 7 degrees C and 42 degrees C. Thermodynamic parameters for Kazal inhibitor binding to the Ile-Val:zymogen adduct are more favorable than those observed for inhibitor association to the free proenzyme, but less so than those reported for beta-trypsin:Kazal inhibitor adduct formation (even under saturating dipeptide concentrations), suggesting that the effector dipeptide does not induce a complete rigidification of the proenzyme's activation domain. Considering the dependence of the association equilibrium constant for Kazal inhibitor binding to trypsinogen from Ile-Val concentration, thermodynamic parameters for the effector dipeptide binding to the free proenzyme and to its binary complex with Kazal inhibitor have been obtained. Differences in affinity for Ile-Val binding to the free zymogen and its binary complexes with inhibitors and substrates are indicative of the presence of different activation levels of the proenzyme, none of them exactly coincident with that of beta-trypsin. Such different discrete states should correspond to those involved in the zymogen-to-active-enzyme transition which should not be considered as an all-or-nothing process, but as a multistep event.
在7℃至42℃、pH 5.5的条件下，研究了异亮氨酸 - 缬氨酸浓度（高达2.0 M）对猪胰分泌型胰蛋白酶抑制剂（卡扎尔抑制剂）与胰蛋白酶原结合的热力学参数的影响。卡扎尔抑制剂与异亮氨酸 - 缬氨酸：酶原加合物结合的热力学参数比抑制剂与游离酶原结合时更有利，但比β-胰蛋白酶：卡扎尔抑制剂加合物形成时报道的参数要低（即使在饱和二肽浓度下），这表明效应二肽不会诱导酶原激活域完全刚性化。考虑到卡扎尔抑制剂与胰蛋白酶原结合的缔合平衡常数对异亮氨酸 - 缬氨酸浓度的依赖性，已获得效应二肽与游离酶原及其与卡扎尔抑制剂二元复合物结合的热力学参数。异亮氨酸 - 缬氨酸与游离酶原及其与抑制剂和底物的二元复合物结合亲和力的差异表明酶原存在不同的激活水平，其中没有一个与β-胰蛋白酶的激活水平完全一致。这种不同的离散状态应对应于酶原向活性酶转变过程中涉及的状态，不应将其视为一个全或无的过程，而应视为一个多步骤事件。
