Kramer J D, Bogitsh B J
Exp Parasitol. 1985 Oct;60(2):163-70. doi: 10.1016/0014-4894(85)90019-0.
The biochemical characterization of dipeptidyl aminopeptidase II activity was investigated in the supernatant of centrifuged homogenates of adult Schistosoma japonicum using a lysine-alanine oligopeptide derivative of 4-methoxy-2-naphthylamide as a substrate. It was observed that the pH optimum of the enzyme is in the acid range, with an optimum at pH 6.3. Time and enzyme concentration studies, along with temperature studies, support the premise that the reaction is enzymatic. The Km was 3.3 X 10(-3) M, at pH 5.5 and 37 C. Tris and diisopropyl phosphofluoridate, when incorporated into the assay system at final concentrations of 500 and 2 mM, respectively, significantly inhibited the reaction by 70.9 and 75%, respectively. Leupeptin (5 X 10(-4) mM) had no effect. The results indicate that the enzyme under study in the present investigation strongly resembles mammalian dipeptidyl aminopeptidase II due to its affinity for substrate, sensitivity to Tris and diisopropyl phosphofluoridate inhibition, and pH optimum. Its inhibition by diisopropyl phosphofluoridate indicates that it may belong to the serine class of proteases. Cytochemical studies revealed reaction product in the lipid-like globules in the gastrodermis, adding further credence that these globules are lysosomal.
以4-甲氧基-2-萘酰胺的赖氨酸-丙氨酸寡肽衍生物为底物，对日本血吸虫成虫匀浆离心后的上清液中的二肽基氨基肽酶II活性进行了生化特性研究。结果发现，该酶的最适pH值在酸性范围内，pH 6.3时为最佳。时间、酶浓度研究以及温度研究均支持该反应为酶促反应这一前提。在pH 5.5和37℃条件下，Km为3.3×10(-3)M。将Tris和二异丙基氟磷酸分别以500 mM和2 mM的终浓度加入测定体系时，分别显著抑制反应70.9%和75%。亮肽素（5×10(-4) mM）无作用。结果表明，本研究中所研究的酶由于其对底物的亲和力、对Tris和二异丙基氟磷酸抑制的敏感性以及最适pH值，与哺乳动物二肽基氨基肽酶II极为相似。其被二异丙基氟磷酸抑制表明它可能属于丝氨酸蛋白酶类。细胞化学研究显示，胃皮中的类脂小球中有反应产物，进一步证明这些小球是溶酶体。
