Mode of cleavage of pig big endothelin-1 by chymotrypsin. Production and degradation of mature endothelin-1

Pig endothelin-1 [ET-1-(1-21)] seems to be produced via proteolytic processing between Trp-21 and Val-22 of an intermediate form consisting of 39 amino acid residues, termed big ET-1-(1-39), by a chymotrypsin-like proteinase. We examined the chymotryptic-cleavage sites of big ET-1-(1-39) by reverse-phase h.p.l.c. and sequence analysis, and found that chymotrypsin cleaved initially the Tyr-31-Gly-32 bond of big ET-1-(1-39), followed by cleavage between Trp-21 and Val-22. Furthermore, chymotrypsin hydrolysed the generated ET-1-(1-21), producing a single major product that had the same amino acid sequence as ET-1-(1-21) with a cleavage between Tyr-13 and Phe-14. The disulphide bridge between Cys-1 and Cys-15 remained intact. These results indicate that the conversion of big ET-1-(1-39) into ET-1-(1-21) catalysed by chymotrypsin requires hydrolysis of the Tyr-31-Gly-32 bond before that of the Trp-21-Val-22 bond, an event followed by cleavage between Tyr-13 and Phe-14 within the loop of ET-1-(1-21). Thus a chymotrypsin-like proteinase might be involved not only in the production but also in the degradation of ET-1-(1-21) in vivo.