Deddish P A, Jackman H L, Skidgel R A, Erdös E G
University of Illinois College of Medicine at Chicago, Department of Pharmacology, 60612, U.S.A.
Biochem Pharmacol. 1997 May 15;53(10):1459-63. doi: 10.1016/s0006-2952(97)00087-7.
The hydrolysis of enkephalin (Enk) congeners by the isolated N- (N-ACE) and C-domain of angiotensin I converting enzyme (ACE) and by the two-domain somatic ACE was investigated. Both Leu5- and Met5-Enk were cleaved faster by the C-domain than by N-ACE; rates with somatic ACE were 1600 and 2500 nmol/min/nmol enzyme with both active sites being involved. Substitution of Gly2 by D-Ala2 reduced the rate to 1/3rd to 1/7th of that of the Enks. N-ACE cleaved Met5-Enk-Arg6-Phe7 faster than the C-domain, probably with the highest turnover number of any naturally occurring ACE substrate (7600 min(-1)). This heptapeptide is also hydrolyzed in the absence of Cl-, but the activation by Cl- is unique; Cl- enhances the hydrolysis of the heptapeptide by N-ACE but inhibits it by the C-domain, yielding about a 5-fold difference in the turnover number at physiological pH. This difference may result in the predominant role of the N-domain in converting Met5-Enk-Arg6-Phe7 to Enk in vivo.
研究了血管紧张素I转换酶（ACE）的分离N-（N-ACE）和C结构域以及双结构域体ACE对脑啡肽（Enk）同系物的水解作用。亮氨酸脑啡肽（Leu5-Enk）和甲硫氨酸脑啡肽（Met5-Enk）被C结构域切割的速度比被N-ACE切割的速度更快；体ACE切割这两种脑啡肽的速率分别为1600和2500 nmol/分钟/纳摩尔酶，两个活性位点均参与其中。将甘氨酸2（Gly2）替换为D-丙氨酸2（D-Ala2）可使切割速率降至脑啡肽的1/3至1/7。N-ACE切割甲硫氨酸脑啡肽-精氨酸6-苯丙氨酸7（Met5-Enk-Arg6-Phe7）的速度比C结构域更快，其周转率可能是任何天然ACE底物中最高的（7600分钟-1）。这种七肽在无氯离子（Cl-）的情况下也会被水解，但Cl-的激活作用很独特；Cl-可增强N-ACE对该七肽的水解作用，但会抑制C结构域对其的水解作用，在生理pH值下，周转率相差约5倍。这种差异可能导致N结构域在体内将Met5-Enk-Arg6-Phe7转化为脑啡肽中起主要作用。
