Purification and characterization of a neutral endopeptidase-like enzyme from human urine

Objective The aims of this study were to purify and characterize a neutral endopeptidase-like enzyme (NEP-like) in human urine end propose a rapid, se nsitive and specific assay for this enzyme using the fluorogenic substrate Abz-FDQ-EDDnp, where Abz = O-aminobenzoic acid and EDDnp = N-(2,4-dinitroph enyl)ethylenediamine. Methods Soluble urinary NEP was purified from human urine using a DEAE-cell ulose Cellex D column and gel filtration on an AcA-44 column. NEP-like acti vity was assayed by its ability to hydrolyse bradykinin (BK) and the fluoro genic substrates Abz-BKQ-EDDnp and Abz-FDQ-EDDnp. The K-m was determined us ing Abz-FDQ-EDDnp as a substrate. The hydrolysis products of BK and Abz-FDQ -EDDnp were analysed by high-performance liquid chromatography (HPLC). The mel. wt was estimated by polyacrylamide gel electrophoresis and the enzyme analysed by Western blot using the antibody obtained from purified recombin ant NEP expressed in Pichia pastoris yeast. Results The NEP-like was purified from human urine until homogeneity and pr esented a mol. wt of 94 000. The substrate Abz-FDQ-EDDnp was selectively hy drolysed at the F-D bond by NEP-like and by recombinant NEP. For this subst rate, the NEP-like activity was maximal at pH 7.0, although a small peak of activity was observed at pH 8.0, and the determined K-m was 14 mu M. The e nzymatic activity was inhibited by thiorphan and phosphoramidon, In Western blot analysis, NEP-like reacted strongly with a polyclonal antibody for NE P. Conclusion A NEP-like enzyme was purified from human urine. Based on the me l. wt of the isolated NEP-like enzyme, it was concluded that this enzyme wa s produced in the kidney. In the kidney, this enzyme may cleave the kinins filtered through the glomerulus and also the kinins produced in the distal nephron. An internally quenched fluorogenic peptide, Abz-FDQ-EDDnp, was sel ectively hydrolysed by NEP-like and by recombinant NEP. J Hypertens 1998, 1 6:1971-1978 (C) 1998 Lippincott Williams & Wilkins.