Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University, Gakuen-cho, Fukuyama 729-0292, Japan.
Arch Biochem Biophys. 2012 Sep 1;525(1):71-81. doi: 10.1016/j.abb.2012.05.018. Epub 2012 Jun 5.
Dipeptidyl peptidase III (DPP III), the zinc peptidase, has a unique helix portion in the metal-binding motif (HELLGH). The enzyme activity of the cupric derivative of rat DPP III (Cu(II)-rat DPP III) for Lys-Ala-β-NA is about 30% of that of the wild-type enzyme. On the other hand, the enzyme activity of Cu(II)-rat del-DPP III, in which Leu453 is deleted from the metal-binding motif, possesses only 1-2% of the enzyme activity of rat del-DPP III. The EPR spectra of Cu(II)-rat DPP III in the presence of various concentrations of the substrate, Lys-Ala-β-NA, changed dramatically, showing formation of the enzyme-metal-substrate complex. The EPR spectra of Cu(II)-rat del-DPP III did not change in the presence of excess Lys-Ala-β-NA. The deletion of Leu453 from the HELLGH motif of rat DPP III leads to a complete loss of flexibility in the ligand geometry around the cupric ions. Under the formation of the enzyme-metal-substrate complex, Glu451 of Cu(II)-rat DPP III is sufficiently able to approach the water molecule via a very different orientation from that of the resting state; however, Glu451 of Cu(II)-rat del-DPP III is not able to access the water molecule.
二肽酰肽酶 III（DPP III），锌肽酶，在金属结合基序（HELLGH）中有一个独特的螺旋部分。大鼠 DPP III 的铜衍生物（Cu(II)-rat DPP III）对 Lys-Ala-β-NA 的酶活性约为野生型酶的 30%。另一方面，金属结合基序中缺失 Leu453 的 Cu(II)-rat del-DPP III 的酶活性仅为大鼠 del-DPP III 的 1-2%。在存在各种浓度的底物 Lys-Ala-β-NA 的情况下，Cu(II)-rat DPP III 的 EPR 光谱发生了剧烈变化，显示出酶-金属-底物复合物的形成。Cu(II)-rat del-DPP III 的 EPR 光谱在存在过量 Lys-Ala-β-NA 的情况下没有变化。大鼠 DPP III 的 HELLGH 基序中 Leu453 的缺失导致配体几何形状围绕铜离子的灵活性完全丧失。在形成酶-金属-底物复合物的过程中，Cu(II)-rat DPP III 的 Glu451 能够通过与静止状态完全不同的方向充分接近水分子；然而，Cu(II)-rat del-DPP III 的 Glu451 不能接近水分子。
