MECHANISM OF ACTION OF CYSTEINE PROTEINASES - OXYANION BINDING-SITE IS NOT ESSENTIAL IN THE HYDROLYSIS OF SPECIFIC SUBSTRATES
MECHANISM OF ACTION OF CYSTEINE PROTEINASES - OXYANION BINDING-SITE IS NOT ESSENTIAL IN THE HYDROLYSIS OF SPECIFIC SUBSTRATES
复制标题
DOI：
10.1021/bi00324a010
复制
发表时间：
1985-01-01
期刊：
影响因子：
2.9
通讯作者：
POLGAR, L
中科院分区：
文献类型：
--
作者：
ASBOTH, B;STOKUM, E;POLGAR, L
为了研究半胱氨酸蛋白酶、木瓜蛋白酶、木瓜凝乳蛋白酶、木瓜肽酶A和无花果蛋白酶催化过程中形成的四面体中间体的氧负离子的可能稳定性，合成了N-（苄氧羰基）苯丙氨酰硫代甘氨酸O-乙酯，并将其水解与上述酶的高度特异性底物相应的氧酯的水解进行了比较。硫取代羰基氧对酰化反应的二级速率常数几乎没有影响，脱酰反应的催化活性降低了约1个数量级。这些结果对比与丝氨酸蛋白酶，其中不能检测到的水解的硫代酯。从结果中可以得出以下结论。在氧阴离子结合位点的四面体中间体的稳定化对于半胱氨酸蛋白酶不是必需的。由于缺乏一般的碱催化，半胱氨酸蛋白酶具有比丝氨酸蛋白酶更少限制的过渡态结构。
To study the possible stabilization of the oxyanion of the tetrahedral intermediate formed in the course of the catalyses by cysteine proteinases, papain, chymopapain, papaya peptidase A and ficin, N-(benzyloxycarbonyl)phenylalanylthioglycine O-ethyl ester was synthesized and its hydrolysis compared with that of the corresponding oxygen ester, a highly specific substrate of the above enzymes. The substitution of sulfur for the carbonyl oxygen hardly affected the 2nd-order rate constant of acylation and diminished catalytic activity by about 1 order of magnitude in deacylation. These results contrast with those obtained with serine proteinases, where the hydrolysis of thiono esters could not be detected. From the results the following conclusions can be drawn. Stabilization of the tetrahedral intermediate at an oxyanion binding site is not essential with cysteine proteinases. Because of the lack of general base catalysis, cysteine proteinases have a less constrained transition-state structure than serine proteinases.