Angiotensin-converting enzyme (ACE) has both somatic and testicular isozymes, the former possessing two catalytically active domains, amino-terminal and carboxyl-terminal, while the latter has only the carboxyl-terminal one. We compared hydrolysis processes of the nonapeptide β-neoendorphin by the two isozymes of human ACE. Both isozymes hydrolyzed the peptide to Tyr1-Gly2-Gly3 by the sequential removal of carboxyl-terminal dipeptides in three consecutive steps. The rate constant values for the second step, conversion of β-neoendorphin1-7 to Leu-enkephalin, by the somatic isozyme in the presence of 10 or 200 mM NaCl were 4-fold higher than those for the first step, conversion of β-neoendorphin1-9 to β-neoendorphin1-7. The k(cat) values of the somatic isozyme for β-neoendorphin1-7 were 2-fold higher than those for β-neoendorphin1-9, indicating that β-neoendorphin1-7 is more rapidly hydrolyzed than β-neoendorphin1-9. The rate constant value for the second step at 10 mM NaCl was 5-fold higher than that for the testicular isozyme. Similar extent of difference was also observed in k(cat) values for β-neoendorphin1-7 between the two isozymes. These results suggest that the amino-terminal domain of the somatic isozyme mainly contributes to the conversion of β-neoendorphin1-7 to Leu-enkephalin at a low NaCl concentration. Optimal chloride concentrations for the individual steps of β-neoendorphin1-9 hydrolysis differed between the two isozymes.
|Number of pages||8|
|Journal||Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology|
|Publication status||Published - Apr 25 1997|
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology