Phosphoramidon endopeptidases

Because renal vasodilatation and hyperfiltration are often associated with a natriuretic response, a number of activators or inhibitors of endogenous vasoactive systems can cause increased NaCl excretion, and some of these may be developed into compounds of clinical interest in special situations. Such agents include natriuretic pqDtides most notably B-type natriuretic peptide (nesiritide), neutral endopeptidase (NEP) inhibitors (thiorphan, phosphoramidon), mixed NEP and ACE inhibitors (omapatrilat), guanylin and uroguanylin, kinins, prostaglandins of the E series, adrenomedullin, relaxin, prolactin, and others. 

C. Oefner, A. D Arcy, M. Hennig, F. K. Winkler, G. E. Dale, Structure of Human Neutral Endopeptidase Complexed with Phosphoramidon , Protein Data Bank ID ldmt, 1999 (H. M. Berman, J. Westbrook, Z. Feng, G. Gilliland, T. N. Bhat, H. Weissig, I. N. Shindyalov, P. E. Bourne, The Protein Data Bank , Nucleic Acids Res. 2000, 28, 235-242). 

Neutral endopeptidase 1,10-Phenanthroline, phosphoramidon, thiorphan [(2-mercaptomethyl-3-phenyl-propionylamino)-acetic acid]... 

Neuropeptide degradation in vertebrates involves both soluble and membrane associated enzymes (1121 Similar mechanisms probably exist in insects. In fact, both soluble and membrane-bound proteolytic activities directed at bioactive peptides have been demonstrated in insect systems (107-1101 A vertebrate-like endopeptidase activity, the Zn-metalloendoprotease (endopeptidase-24 l 1), is present in the locust and is sensitive to the specific inhibitor, phosphoramidon (107-108.1111... 

The generally accepted view is that ECE is a metalloprotease. Enzymes of this type have been isolated from a variety of tissue sources including cultured endothelial cells [65], vascular smooth muscle [66], human umbilical vein [67] and human brain [68], and have been characterized as neutral endopeptidases sensitive to phosphoramidon. Several groups have demonstrated an endothelial cell derived ECE which is active at neutral pH and inhibited by phosphoramidon and other metal chelators, but not by... 

The most conserved segment of the L chain of CNTs is a central region that contains a His-Glu-Xaa-Xaa-His zinc-binding motif characteristic of zinc-endopeptidases, thus suggesting that TeTx and the BoNTs may inhibit neuroexocytosis through a zinc-endopeptidase activity. This hypothesis was confirmed with two experimental approaches in Aply-sia neurons. First, the lack of toxicity of the apo-TeTx L chain demonstrated the essential role of the metal atom in toxin activity (Schiavo et ai, 1992 a, b). Second, phosphoramidon, a very specific inhibitor of zinc-endopeptidases, was shown to inhibit TeTx-induced blockade of ACh release (Schiavo ef ai, 1992 b). These results were the first clear evidence that the L chain of TeTx was acting via a metallo-protease activity. 

Inhibitors include thiorphan, phosphoramidon and SCH 32615, See neutral endopeptidase inhibitors. 

Endothelin converting enzyme (ECE) has yet to be fully characterized. It is a membrane-located enzyme found in the vascular endothelium. It is essential in the production of endothelin in the body since it converts the inactive precursor big ET-1 to endothelin-1. It is an unusual enzyme because it cleaves at a Tyr-Val link. Like endopeptidase-24.11, it is inhibited by phosphoramidon (so is a metalloproteinase), and these two enzymes are often colocated. Furthermore, monoclonal antibody co-precipitation studies indicate they share a common epitope, and a homology to the extent of about 39%, ECE is also similar to the bacterial metalloprotease thermolysin, but is more specific. If a specific inhibitor is discovered that can act in vivo, then clearly such a drug could modulate endothelin production throughout the body, which would have important consequences (e.g. in antihypertensive therapy). 

Takahama K, Fuchikami J, Kai H, Isohama Y, Miyata T (1995) Inhalation of phosphoramidon, a neutral endopeptidase inhibitor, induces cough in awake guinea-pigs. Arch Int Pharmacodyn Ther 330 241-250... 

---