Investigations on the functional role of angiotensin converting enzyme (ACE) in human seminal plasma.

The investigations were carried out with partially purified angiotensin converting enzyme (E.C.3.4.15.1) from human seminal plasma and from human blood plasma. The Km-constants for angiotensin converting enzyme (ACE) from both sources, estimated by the use of synthetic substrates, were in the same order. The catalytic properties of the enzymes were characterized by a series of known peptidase inhibitors. The male antifertility drug gossypol (1,1',6,6',7,7'-hexahydroxy-3,3'-dimethyl-5,5'-bis-isopropyl-(2,2' -naphthalene)--8,8'-dicarboxaldehyde) was identified as a potent ACE-inhibitor. The inhibitory constants of several kinins and other biologically active peptides were determined. Any regulatory influence of the peptides investigated on the ACE-activity in vivo is not probably. The inhibitor of Zn-containing metalloproteases 2-(N-hydroxycarboxamido)-4-methylpentanoyl-L-alanylglycin e amide) (Zinkov) selectively inhibited ACE from blood plasma, whereas ACE from seminal plasma was not influenced. In seminal plasma the majority of the enzyme is associated with macromolecular structures, identified as membrane vesicles. These vesicles contain also other enzymatic activities usually detectable in seminal plasma. In the male genital tract ACE is synthesized in the prostate, epididymis and testis. As our data indicate ACE seems not to be involved in the regulation of sperm motility.