McPhie P
Biophys Chem. 1979 May;9(4):281-7.
At alkaline pH, swine pepsinogen is reversibly inactivated in a transition which involves the cooperative release of two protons from the molecule and is governed by a pK = 9. Stopped flow kinetic studies on the absorbance changes accompanying this reaction show that it can be resolved into two steps, with increasing pH; a slow conformational change, whose amplitude follows the ionisation curve of one group of pK = 9.9, followed by a rapid pH dependent conformational change, linked to a group of pK = 8.2. The pH dependence of the rate of the slow step is interpreted to show the presence of a protonated group which cannot ionise in the neutral form of the zymogen, but is in slow equilibrium with a form where it titrates with a pK 6.8. At the same time, a histidine in the amino terminal region of the protein becomes reactive to diethyl pyrocarbonate, suggesting this to be the group which triggers the reaction.
在碱性pH条件下，猪胃蛋白酶原会发生可逆失活，此转变过程涉及从分子中协同释放两个质子，且受pK = 9的控制。对该反应伴随的吸光度变化进行的停流动力学研究表明，随着pH升高，它可分为两个步骤：一个缓慢的构象变化，其幅度遵循一组pK = 9.9基团的电离曲线，随后是一个与一组pK = 8.2基团相关的快速pH依赖性构象变化。慢步骤速率的pH依赖性被解释为表明存在一个质子化基团，该基团在酶原的中性形式中不能电离，但与一种以pK 6.8进行滴定的形式处于缓慢平衡状态。与此同时，蛋白质氨基末端区域的一个组氨酸对焦碳酸二乙酯变得有反应性，表明这是触发反应的基团。
