Vajda T, Szabó T
Acta Biochim Biophys Acad Sci Hung. 1976;11(4):287-94.
Steady state kinetics of the hydrolysis by trypsin and chymotrypsin of the ethyl esters of the N-acetyl derivatives of glycine, L-alanine, DL-2-aminobutyric acid, L-norvaline, L-valine, L-norleucine and L-leucine were studied at pH 6.6 and 25 degrees C. It is apparent from the second-order rate constants, kcat/Km, app, that there is a significant difference between the specificities of the two enzymes toward substrates with a long side chain, such as the derivatives of norvaline, norleucine and leucine. The carboxylate ion Asp-189 in the specificity pocket of trypsin seems to interfere with the productive binding of substrates containing apolar side chains longer than those of the derivatives of DL-2-aminobutyric acid or L-valine. The basic group of the specific substrates of trypsin, such as that of lysine and arginine derivatives, promotes the binding of the apolar side chain by neutralizing the negative carboxylate ion of Asp-189.
在pH 6.6和25℃条件下，研究了胰蛋白酶和糜蛋白酶对甘氨酸、L-丙氨酸、DL-2-氨基丁酸、L-正缬氨酸、L-缬氨酸、L-正亮氨酸和L-亮氨酸的N-乙酰衍生物乙酯的水解稳态动力学。从二级速率常数kcat/Km, app可以明显看出，这两种酶对具有长侧链的底物（如正缬氨酸、正亮氨酸和亮氨酸的衍生物）的特异性存在显著差异。胰蛋白酶特异性口袋中的羧酸根离子Asp-189似乎会干扰含有比DL-2-氨基丁酸或L-缬氨酸衍生物更长的非极性侧链的底物的有效结合。胰蛋白酶特异性底物的碱性基团（如赖氨酸和精氨酸衍生物的碱性基团）通过中和Asp-189的负羧酸根离子来促进非极性侧链的结合。
