McPhie P
Biochemistry. 1975 Dec 2;14(24):5253-6. doi: 10.1021/bi00695a003.
Above pH 8.5, pepsinogen is converted into a form which cannot be activated to pepsin on exposure to low pH. Intermediate exposure to neutral pH, however, returns the protein to a form which can be activated. Evidence is presented for a reversible, small conformational change in the molecule, distinct from the unfolding of the protein. At the same time, the molecule is converted to a form of limited solubility, which is precipitated at low pH, where activation is normally seen. The results are interpreted in terms of the peculiar structure of the pepsinogen molecule. Titration of the basic NH2-terminal region produced an open form, which can return to the native form at neutral pH, but which is maintained at low pH by neutralization of carboxylate groups in the pepsin portion.
在pH 8.5以上，胃蛋白酶原会转变为一种形式，该形式在暴露于低pH值时无法被激活为胃蛋白酶。然而，中间暴露于中性pH值会使该蛋白质恢复为可被激活的形式。有证据表明，分子中存在一种可逆的、微小的构象变化，这与蛋白质的展开不同。同时，分子转变为溶解度有限的形式，在通常可见激活作用的低pH值下会沉淀。这些结果根据胃蛋白酶原分子的特殊结构进行了解释。对碱性NH2末端区域的滴定产生了一种开放形式，该形式在中性pH值下可恢复为天然形式，但在低pH值下通过胃蛋白酶部分中羧酸盐基团的中和作用得以维持。
