Chu T G, Orlowski M
Endocrinology. 1985 Apr;116(4):1418-25. doi: 10.1210/endo-116-4-1418.
A soluble metalloendopeptidase identified in rat brain, preferentially cleaves bonds in peptides having hydrophobic amino acid residues in the P1, P2, and P3' positions. (The nomenclature of T. Schechter and A. Berger is used to describe the interaction between enzyme and substrate. The amino acid residues in the substrate are designated as P1, P2, P3 etc. in the N-terminal direction and P1', P2', P3' etc. in the C-terminal direction from the bond undergoing cleavage. The corresponding subsites in the enzyme are identified by the letter S.) The degradation of a series of biologically active peptides and their affinity toward the enzyme was studied. Dynorphin-(1-8), alpha-neo-endorphin, and beta-neo-endorphin are rapidly hydrolyzed to form leu-enkephalin, whereas bovine adrenal medulla dodecapeptide is hydrolyzed to form met-enkephalin. The enzyme, however, does not cleave a larger precursor molecule of metenkephalin, such as bovine adrenal medulla docosapeptide. Several other bioactive peptides are also cleaved at sites consistent with our previously reported specificity studies. Met- and leu-enkephalin are resistant to hydrolysis. The binding affinity [as expressed by inhibitory constant (Ki) or Michaelis-Menten constant (Km) values] of several bioactive peptides such as dynorphin-(1-8), beta-neo-endorphin, neurotensin, angiotensin I, and bradykinin was found to be in the micromolar range. These peptides were also rapidly hydrolyzed by the enzyme, showing, as a result, high specificity constants (kcat/Km values). The highest enzyme activity was found in brain, testis, and in the anterior and posterior lobes of the pituitary, while the activity in such tissues as spleen, liver, kidney, lung, adrenals, and thyroid amounted to only 10-20% of that found in brain. This distribution of enzyme activity, together with its preference for oligopeptides as substrates, its ability to generate leu- and met-enkephalin from several larger peptide precursors, and its affinity toward several other bioactive peptides, suggests that the enzyme functions in the metabolism of neuropeptides.
在大鼠脑中鉴定出的一种可溶性金属内肽酶，优先切割在P1、P2和P3'位置具有疏水氨基酸残基的肽中的键。（采用T. Schechter和A. Berger的命名法来描述酶与底物之间的相互作用。底物中的氨基酸残基在N端方向从切割的键开始依次指定为P1、P2、P3等，在C端方向依次指定为P1'、P2'、P3'等。酶中相应的亚位点用字母S表示。）研究了一系列生物活性肽的降解及其对该酶的亲和力。强啡肽-(1-8)、α-新内啡肽和β-新内啡肽迅速水解形成亮氨酸脑啡肽，而牛肾上腺髓质十二肽水解形成甲硫氨酸脑啡肽。然而，该酶不切割甲硫氨酸脑啡肽的较大前体分子，如牛肾上腺髓质二十二肽。其他几种生物活性肽也在与我们先前报道的特异性研究一致的位点被切割。甲硫氨酸脑啡肽和亮氨酸脑啡肽对水解具有抗性。发现几种生物活性肽如强啡肽-(1-8)、β-新内啡肽、神经降压素、血管紧张素I和缓激肽的结合亲和力[以抑制常数(Ki)或米氏常数(Km)值表示]在微摩尔范围内。这些肽也被该酶迅速水解，因此显示出高特异性常数(kcat/Km值)。在脑、睾丸以及垂体的前叶和后叶中发现最高的酶活性，而在脾脏、肝脏、肾脏、肺、肾上腺和甲状腺等组织中的活性仅为脑中活性的10%-20%。这种酶活性的分布，连同其对寡肽作为底物的偏好、从几种较大肽前体生成亮氨酸和甲硫氨酸脑啡肽的能力以及对其他几种生物活性肽的亲和力，表明该酶在神经肽代谢中起作用。
