In the present study, we purified α-amino acid ester hydrolase (AEH) from cell-free extracts of the Stenotrophomonas maltophilia strain HS1. The approximately 70-kDa AEH from S. maltophilia HS1 (SmAEH) was homogeneous in sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analyses, and was present as a tetramer in gel-filtration experiments. The activity of the SmAEH enzyme was then determined by monitoring the synthesis of the antihypertensive agent dipeptide isoleucyl-tryptophan (Ile-Trp) from isoleucyl methyl ester (Ile-OMe) and tryptophan (Trp). In these experiments, SmAEH had wide substrate specificity for acyl donors, such as Gly-OMe, β-Ala-OMe, Pro-OMe and Trp-OMe and Ile-OMe, and maximal activity were observed under conditions of pH 9.0 and 30 °C. SmAEH also showed the greatest stability at pH 9.0, whereas its activity was reduced by 40% after 10-min incubation at approximately 50 °C. In subsequent activity assays in the presence of various metal ions, Ag+ strongly inhibited enzyme activity. Finally, SmAEH activity was completely inhibited by phenylmethanesulfonyl fluoride (PMSF), suggesting that the protein is a serine protease.
在本研究中,我们从Stenotrophomonas maltophilia HS1菌株的无细胞
提取物中纯化了
α-氨基酸酯
水解酶(AEH)。来自S. maltophilia HS1的约70 kDa AEH(SmAEH)在
十二烷基硫酸钠聚
丙烯酰胺凝胶电泳(
SDS-PAGE)分析中表现为均一,并在凝胶过滤实验中以四聚体形式存在。然后通过监测抗高血压药物二肽
异亮氨酸-色
氨酸(Ile-Trp)从
异亮氨酸甲酯(Ile-OMe)和色
氨酸(Trp)的合成来确定SmAEH酶的活性。在这些实验中,SmAEH对酰基供体表现出广泛的底物特异性,如Gly-OMe、β-Ala-OMe、Pro-OMe和Trp-OMe以及Ile-OMe,并且在pH 9.0和30°C条件下观察到最大活性。SmAEH在pH 9.0下也表现出最大的稳定性,而在约50°C下孵育10分钟后,其活性降低了40%。在后续的活性测定中,存在各种
金属离子时,Ag+对酶活性有强烈抑制作用。最后,SmAEH活性被
苯甲基磺酰氟(
PMSF)完全抑制,表明该蛋白是一种
丝氨酸蛋白酶。