CHARACTERIZATION OF NEUTRAL ENDOPEPTIDASE-24.11 IN DOG GLOMERULI

Neutral endopeptidase (NEP; also known as neprilysin and enkephalinase ; EC 3.4.24.11) is a cell-surface metallopeptidase that is present in many mammalian tissues. It is particularly abundant on the brush-borde r membranes of the kidney proximal tubule. In this paper, the presence of NEP in purified glomeruli from dog kidney was assessed by measurin g phosphoramidon- and thiorphan-sensitive [D-Ala2Leu5]enkephalin-degra ding activity. Using this assay, the K(m) and k(cat) of the glomerular enzyme were found to be identical to those of the tubular enzyme. By Western blotting the apparent M(r) of the glomerular enzyme was found to be 104000, compared with 94000 for the tubular enzyme. This might b e due to a different glycosylation pattern, since endoglycosidase F tr eatment of NEP obtained from both tissues yielded deglycosylated enzym es with similar electrophoretic mobilities. The glomerular enzyme also appears to be membrane-bound, since it was retained in the detergent- rich phase after phase separation with Triton X-114. Auto-radiography experiments performed with RB104, a new highly selective and potent NE P inhibitor, showed that NEP was expressed in both glomeruli and proxi mal tubules. The presence in glomeruli of NEP and some other brush-bor der peptidases (dipeptidyl-dipeptidase IV, aminopeptidase N and angiot ensin I-converting enzyme) suggests that cell-surface peptidases might play an important role as regulators of plasma-derived peptides in th is part of the nephron.