HYDROLYSIS OF BIG ENDOTHELIN-1 BY A SERINE-PROTEASE IN THE MEMBRANE-FRACTION OF HUMAN LUNG

The hydrolysis of human big endothelin(1-38) (bigET-1) was investigate d in the membrane fractions from three human lung specimens. The hydro lysis products were identified by HPLC or by amino acid analysis, pept ide sequencing and mass spectrometry, and the contractile effects of s ynthetic bigET-1, synthetic ET-1 and the major metabolite were tested on isolated rabbit pulmonary arteries. The dominating hydrolysis produ ct was identified as bigET(1-31), formed by a chymostatin-sensitive en zyme. Soybean trypsin inhibitor also suppressed bigET(1-31) formation, while two other serine protease inhibitors, 3,4-dichloroisocoumarin a nd aprotinin, had no (or a limited) inhibitory effect. Through a partl y phosphoramidon-sensitive enzymatic activity, endothelin-1 (ET-1) was formed independently of bigET(1-31). On isolated pulmonary arteries, bigET(1-31) had a contractile effect similar to that of synthetic bigE T-1, with pEC(50%) values of 7.3+/-0.1 (n = 6) and 7.1+/-0.1 (n = 8), respectively. The pEC(50%) value of ET-1 was 9.2+/-0.3 (n = 6). These results indicate that human pulmonary membranes, besides hydrolysing b igET-1 to ET-1, also express serine protease activity that is responsi ble for the formation of the biologically active product, bigET(1-31). (C) 1997 Elsevier Science B.V.