Gilbert H J, Jack G W
Biochem J. 1981 Dec 1;199(3):715-23. doi: 10.1042/bj1990715.
Phenylalanine ammonia-lyase (EC 4.3.1.5) of the yeast Rhodotorula glutinis was rapidly inactivated by duodenal juice. It was susceptible to chymotrypsin and subtilisin and to a lesser extent trypsin. Initial proteolysis of the enzyme by chymotrypsin and trypsin resulted in cleavage of the monomeric subunit (75 000 Mr) into a large (65 000 Mr) and a small (10 000 Mr) peptide. The small peptide was rapidly degraded. The 65 000-Mr fragment was resistant to prolonged incubation with chymotrypsin, but was degraded by trypsin under the same conditions. Phenylalanine ammonia-lyase was cleaved into several polypeptides by subtilisin, the 65 000-Mr peptide being totally absent. The N-terminal region of the enzyme was contained in the 65 000-Mr fragment, as was the dehydroalanine moiety, the prosthetic group. Active-site-binding ligands protect the enzyme from inactivation by the three proteinases, and peptide-bond cleavage by trypsin and chymotrypsin. Several chemical modifications were performed on phenylalanine ammonia-lyase. Some decreased its antigenicity, and ethyl acetimidate decreased the rate of degradation of the 65 000-Mr peptide by trypsin. The modification did not protect the enzyme from proteolytic inactivation of the enzymic activity. These observations are discussed in terms of the structure of phenylalanine ammonia-lyase and site of action of the proteinases.
粘红酵母的苯丙氨酸解氨酶（EC 4.3.1.5）可被十二指肠液迅速灭活。它对胰凝乳蛋白酶和枯草杆菌蛋白酶敏感，对胰蛋白酶的敏感性稍低。胰凝乳蛋白酶和胰蛋白酶对该酶的初始蛋白水解作用导致单体亚基（75000 Mr）裂解为一个大的（65000 Mr）和一个小的（100 O0 Mr）肽段。小肽段迅速降解。65000-Mr片段在与胰凝乳蛋白酶长时间孵育时具有抗性，但在相同条件下会被胰蛋白酶降解。枯草杆菌蛋白酶将苯丙氨酸解氨酶裂解为几种多肽，65000-Mr肽段完全缺失。该酶的N端区域以及辅基脱氢丙氨酸部分包含在65000-Mr片段中。活性位点结合配体可保护该酶不被三种蛋白酶灭活，以及不被胰蛋白酶和胰凝乳蛋白酶切割肽键。对苯丙氨酸解氨酶进行了几种化学修饰。一些修饰降低了其抗原性，乙酰亚氨酸乙酯降低了65000-Mr肽段被胰蛋白酶降解的速率。这种修饰并未保护该酶免受蛋白水解对酶活性的灭活作用。根据苯丙氨酸解氨酶的结构和蛋白酶的作用位点对这些观察结果进行了讨论。
