A. Schweizer et al., HUMAN ENDOTHELIN-CONVERTING ENZYME (ECE-1) - 3 ISOFORMS WITH DISTINCTSUBCELLULAR LOCALIZATIONS, Biochemical journal, 328, 1997, pp. 871-877
Endothelin-converting enzyme 1 (ECE-1) is a membrane-bound metalloprot
ease that catalyses the conversion of inactive big endothelins into ac
tive endothelins. Two different isoforms (ECE-1a and ECE-1b) have prev
iously been identified for human ECE-1. In the present study we have c
loned a novel human ECE-1 isoform, termed ECE-1c, and have thus shown
for the first time the existence of three distinct ECE-1 isoforms. The
three isoforms differ only in their N-terminal regions and are derive
d from a single gene through the use of alternative promoters. Ribonuc
lease protection experiments revealed that, although the relative leve
ls of the three isoform mRNA species vary between human tissues, ECE-1
c mRNA is generally the predominant isoform messenger. Immunofluoresce
nce microscopy analysis showed distinct subcellular localizations for
the three isoforms: whereas ECE-1a and ECE-1c are localized at the cel
l surface, ECE-1b was found to be intracellular and showed significant
colocalization with a marker protein for the trans-Golgi network. We
determined that the three isoforms have similar kinetic rate constants
(K-m, k(cat) and V-max) for the processing of big endothelin 1 and th
at the big endothelin isoforms 1, 2 and 3 are cleaved with similar rel
ative velocities of 1.0:0.1:0.1 by the three isoenzymes.