Occurrence and potential importance of selected peptidases in bull ejaculates

The zinc containing peptidases angiotensin-converting enzyme (ACE), neutral metalloendopeptidase (NEP), and leucine aminopeptidase (LAP) occur in bull ejaculates in high activities. These enzyme activities are in close correlation with some routineously determined semen parameters. These ejaculat parameters are used for quality classification and selection of ejaculates and are according to long term experience in good correlation to the male fertility. Semen quality related correlations could not be found for the dipeptidyl aminopeptidase (DPIV) and the aminopeptidase A (APA). Origin and possible function of the zinc containing peptidases in the semen are examined and discussed.