Fricker L D, Berman Y L, Leiter E H, Devi L A
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Biol Chem. 1996 Nov 29;271(48):30619-24. doi: 10.1074/jbc.271.48.30619.
Carboxypeptidase E (CPE) is involved in the biosynthesis of many peptide hormones and neurotransmitters. Mice with the fat mutation have previously been found to have a point mutation in the cpe gene, and to have greatly reduced levels of CPE-like enzyme activity in the pituitary and pancreatic islets (Naggert, J. K., Fricker, L. D., Varlamov, O., Nishina, P. M., Rouille, Y., Steiner, D. F., Carroll, R. J., Paigen, B. J., and Leiter, E. H. (1995) Nat. Genet. 10, 135-142). In the present report, we examined CPE-like activity and peptide processing in several tissues of C57BLKS/LtJ-Cpefat/Cpefat mutant (Cpefat/Cpefat) mice. Whereas CPE-like activity is detected in homogenates of Cpefat/Cpefat mouse tissues, the majority of this activity is not due to CPE based on the sensitivity to p-chloromercuriphenyl sulfonate. In addition, the Cpefat/Cpefat activity does not bind to a substrate affinity column under conditions that bind CPE. Furthermore, the enzyme activity and immunoreactive properties of the activity purified from Cpefat/Cpefat brain are distinct from those of CPE. Taken together, these data suggest that CPE is completely inactive in the Cpefat/Cpefat mice, and that all of the CPE-like activity is due to other carboxypeptidases such as carboxypeptidase D. Levels of Leu-enkephalin in Cpefat/Cpefat mouse brain are approximately 5-fold lower than those in control brain. Treatment of the Cpefat/Cpefat brain extract with carboxypeptidase B restores the level of Leu-enkephalin to the level in control brain. Interestingly, the large molecular weight enkephalin-containing peptides are elevated 2-3-fold in Cpefat/Cpefat mouse brain. These data indicate that CPE plays an important role in the processing of peptide hormones in various tissues, but that other carboxypeptidases also contribute to peptide processing. Furthermore, the increase in levels of high molecular weight enkephalin peptides in the Cpefat/Cpefat mouse suggests that CPE is required for efficient peptide processing by the endopeptidases.
羧肽酶E（CPE）参与多种肽类激素和神经递质的生物合成。先前已发现携带肥胖突变的小鼠在cpe基因中存在点突变，且其垂体和胰岛中CPE样酶活性水平大幅降低（纳格特，J.K.，弗里克，L.D.，瓦尔拉莫夫，O.，西 Nishina，P.M.，鲁伊尔，Y.，施泰纳，D.F.，卡罗尔，R.J.，派根，B.J.，和莱特，E.H.（1995年）《自然遗传学》10，135 - 142）。在本报告中，我们检测了C57BLKS/LtJ - Cpefat/Cpefat突变（Cpefat/Cpefat）小鼠多个组织中的CPE样活性和肽加工情况。虽然在Cpefat/Cpefat小鼠组织匀浆中检测到了CPE样活性，但基于对对氯汞苯磺酸的敏感性，这种活性的大部分并非由CPE引起。此外，在能结合CPE的条件下，Cpefat/Cpefat活性并不与底物亲和柱结合。而且，从Cpefat/Cpefat脑部分离纯化出的酶活性及其免疫反应特性与CPE不同。综合这些数据表明，Cpefat/Cpefat小鼠中的CPE完全无活性，所有的CPE样活性都归因于其他羧肽酶，如羧肽酶D。Cpefat/Cpefat小鼠脑内亮脑啡肽水平比对照脑内低约5倍。用羧肽酶B处理Cpefat/Cpefat脑提取物可使亮脑啡肽水平恢复到对照脑内的水平。有趣的是，Cpefat/Cpefat小鼠脑中含脑啡肽的大分子肽升高了2 - 3倍。这些数据表明，CPE在各种组织中肽类激素的加工过程中起重要作用，但其他羧肽酶也参与肽加工。此外，Cpefat/Cpefat小鼠脑中高分子量脑啡肽肽水平的升高表明，CPE是内肽酶高效进行肽加工所必需的。
