HPLC separation of the cleavage products of big ET-1. Big ET-1 was incubated for 2 hours with either wild-type s-Kell or the E582G mutant, and the peptides were separated by HPLC as described in Materials and Methods. The top panel is with wild-type s-Kell and the bottom panel is with the E582G mutant. Peak A is big ET-1 and peaks B and C, noted in the top panel, are the cleaved products.