Laboratories of The Rockefeller Institute for Medical Research, Princeton, N. J.
J Gen Physiol. 1937 Jan 20;20(3):335-52. doi: 10.1085/jgp.20.3.335.
In the presence of iodine at pH 5.0-6.0 a solution of pepsin absorbs iodine and the specific proteolytic activity of the solution decreases. The activity is less than 1 per cent of the original activity when the number of iodine atoms per mol of pepsin is 35-40. If the pH is 4.5 or less, iodine reacts very slowly and there is a correspondingly slower loss in activity. Glycyl tyrosine reacts with iodine in a manner similar to pepsin. Experiments were performed to determine the extent to which oxidation of pepsin by iodine occurs during iodination, and if such oxidation were responsible for the loss in enzymatic activity. Although the results were not absolutely decisive, there seems to be no appreciable oxidation taking place during iodination and no relationship between the slight oxidation and loss in peptic activity. From a dialyzed preparation of completely iodinated pepsin which was inactive and contained 13.4 per cent bound iodine, 82 per cent of the iodine was obtained in a solution which analyzed as a solution of diiodo-tyrosine. Because of the presence of a material which contained no iodine and prevented quantitative crystallization, only 53 per cent of the iodine containing substance could be crystallized. This 53 per cent was, however, identified as diiodo-tyrosine. The part of the titration curve which in pepsin and most proteins represents the phenolic group of tyrosine was, in the curve for iodinated pepsin, shifted toward the acid region as expected. From these results, it appears that the loss in proteolytic activity of pepsin, when treated with iodine under the specified conditions, is due to the reaction of the iodine with the tyrosine in pepsin.
在 pH 值为 5.0-6.0 的条件下，胃蛋白酶溶液会吸收碘，溶液的特定蛋白水解活性会降低。当每摩尔胃蛋白酶的碘原子数为 35-40 时，其活性低于原始活性的 1%。如果 pH 值低于 4.5，碘的反应非常缓慢，活性相应地降低得更慢。甘氨酰酪氨酸与碘的反应方式与胃蛋白酶相似。进行了实验以确定碘代过程中碘对胃蛋白酶的氧化程度，如果这种氧化是导致酶活性丧失的原因。尽管结果并非绝对决定性的，但似乎在碘代过程中没有发生明显的氧化，并且氧化与胃蛋白酶活性丧失之间没有关系。从完全碘化的胃蛋白酶的透析制剂中，该制剂无活性且含有 13.4%结合碘，从分析为二碘酪氨酸溶液中获得了 82%的碘。由于存在一种不含有碘且阻止定量结晶的物质，只能结晶出含碘物质的 53%。然而，该 53%被鉴定为二碘酪氨酸。在胃蛋白酶和大多数蛋白质中代表酪氨酸酚基团的滴定曲线部分，在碘化胃蛋白酶的曲线中，如预期的那样向酸性区域移动。根据这些结果，当在指定条件下用碘处理胃蛋白酶时，胃蛋白酶的蛋白水解活性丧失似乎是由于碘与胃蛋白酶中的酪氨酸反应所致。
