Kinetic evaluation of beta-neoendorphin hydrolysis by the somatic and testicular isozymes of human angiotensin-converting enzyme.
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 beta-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 beta-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 beta-neoendorphin1-9 to beta-neoendorphin1-7. The k(cat) values of the somatic isozyme for beta-neoendorphin1-7 were 2-fold higher than those for beta-neoendorphin1-9, indicating that beta-neoendorphin1-7 is more rapidly hydrolyzed than beta-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 beta-neoendorphin1-7 between the two isozymes. These results suggest that the amino-terminal domain of the somatic isozyme mainly contributes to the conversion of beta-neoendorphin1-7 to Leu-enkephalin at a low NaCl concentration. Optimal chloride concentrations for the individual steps of beta-neoendorphin1-9 hydrolysis differed between the two isozymes.
Hayakari
M
M
Second Department of Biochemistry, Hirosaki University School of Medicine, Japan.
Satoh
K
K
Ookawa
K
K
Kano
H
H
Murakami
S
S
Ikeda
N
N
Tsuchida
S
S
D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008297:Male; D010446:Peptide Fragments / Q000302:isolation & purification; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*; D012965:Sodium Chloride; D013737:Testis / Q000201:enzymology*; D001615:beta-Endorphin / Q000031:analogs & derivatives* / Q000378:metabolism
D007527:Isoenzymes; D010446:Peptide Fragments; D012965:Sodium Chloride; D001615:beta-Endorphin; C030719:beta-neo-endorphin; D007703:Peptidyl-Dipeptidase A