A 105- to 94-kilodalton protein in the epididymal fluids of domestic mammals is angiotensin I converting enzyme (ACE); Evidence that sperm are the source of this ACE
Jl. Gatti et al., A 105- to 94-kilodalton protein in the epididymal fluids of domestic mammals is angiotensin I converting enzyme (ACE); Evidence that sperm are the source of this ACE, BIOL REPROD, 60(4), 1999, pp. 937-945
SDS-PAGE analysis of luminal fluid from the ram testis and epididymis revea
led a protein of about 105 kDa in the fluid in the caput epididymal region.
The molecular mass of this fluid protein shifted from 105 kDa to 94 kDa in
the distal caput epididymidis and remained at 94 kDa in the lower regions
of the epididymis. The possible sperm origin of this protein was suggested
by the decrease in intensity of a 105-kDa compound on the sperm plasma memb
rane extract and by its total disappearance from the fluid of animals with
impaired sperm production caused by scrotal heating.
The 94-kDa protein was purified from ram cauda epididymal fluid, and a rabb
it polyclonal antiserum was obtained. This antiserum showed that membranes
of testicular sperm and sperm from the initial caput were positive for the
presence of an immunologically related antigen. The protein was immunolocal
ized mainly on the flagellar intermediate piece, whereas in some corpus and
caudal sperm, only the apical ridge of the acrosomal vesicle was labeled.
The purified protein was microsequenced: its N-terminal was not found in th
e sequence database, but its tryptic fragments matched the sequence of the
angiotensin I-converting enzyme (ACE). Indeed, the purified 94-kDa protein
exhibited a carboxypeptidase activity inhibited by specific blockers of ACE
. All the soluble seminal plasma ACE activity in the ram was attributable t
o the 94-kDa epididymal fluid ACE. The polyclonal antiserum also showed tha
t a soluble form of ACE appeared specifically in the caput epididymal fluid
of the boar, stallion, and bull. This soluble form was responsible for all
the ACE activity observed in the fluid from the distal caput to the cauda
epididymidis in these species.
Our results strongly suggest that the epididymal fluid ACE derives from the
germinal form of ACE that is liberated from the testicular sperm in a spec
ific epididymal area.