Sanny C G, Hartsuck J A, Tang J
J Biol Chem. 1975 Apr 10;250(7):2635-9.
Exposure of pepsinogen to acid for less than 2 min yields a product with proteolytic activity. This activity is due to intramolecular and intermolecular formation of pepsin from pepsinogen. We find no evidence for intermolecular proteolytic activity in the zymogen. These conclusions are based upon two sets of experiments. First, chemical cleavage of pepsinogen during short activation is demonstrated by quantitative analysis of the NH2-terminal 2 residues of the pepsin and pepsinogen in an activation mixture. In addition, quantitative NH2-terminal analyses after activation under different conditions confirm our previous inference that the product of unimolecular pepsinogen activation is homogeneous whereas bimolecular activation produces a pepsin product with a variety of NH2 termini. Second, spectral changes which occur upon acidification of a pepsinogen solution and are reversed by neutralization are shown to be consistent with the chemical cleavage of pepsinogen during acidification. The first order rate constant for pepsinogen activation, calculated from these spectral experiments, agrees well with the value we had determined previously.
胃蛋白酶原在酸性环境中暴露不到2分钟就会产生具有蛋白水解活性的产物。这种活性是由于胃蛋白酶原分子内和分子间形成了胃蛋白酶。我们在该酶原中未发现分子间蛋白水解活性的证据。这些结论基于两组实验。首先，通过对激活混合物中胃蛋白酶和胃蛋白酶原的NH2末端2个残基进行定量分析，证明了短时间激活过程中胃蛋白酶原的化学裂解。此外，在不同条件下激活后的定量NH2末端分析证实了我们之前的推断，即单分子胃蛋白酶原激活的产物是均匀的，而双分子激活产生的胃蛋白酶产物具有多种NH2末端。其次，胃蛋白酶原溶液酸化时发生的光谱变化并通过中和逆转，表明与酸化过程中胃蛋白酶原的化学裂解一致。从这些光谱实验计算出的胃蛋白酶原激活的一级速率常数与我们之前确定的值非常吻合。
