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CHARACTERISTICS OF THE EPIDIDYMAL SOLUBLE FORM OF GERMINAL ANGIOTENSIN I-CONVERTING ENZYME (ACE). ENZYMATIC PROPERTIES AND RELATIONSHIP WITH SPERM FERTILITY IN VITRO AND IN VIVO.
Métayer, Sonia1, Dacheux, Françoise 1, Guérin, Yvon1, Dacheux, Jean-Louis1, Gatti, Jean-Luc1, 1
ABSTRACT- Germinal angiotensin-I converting enzyme (gACE) has been shown to play an important role in male fertility and the presence of a soluble form of this gACE derived from the sperm membrane has been demonstrated in the epididymal fluid of different mammals1. The ram epididymal fluid form of gACE was purified by chromatography and some of its enzymatic properties studied. This enzyme exhibited a Km of 0.18 mM and a Vmax of 34 moles/(min.mg) for furanacryloyl-L-phenylalanylglycylglycine (FAPGG) and a Km of 2.65 mM and a Vmax of 163 moles/(min.mg) for hippuryl-L-histidyl-L-leucine under defined standard conditions (300 mM NaCl; 50 mM Tris; pH 7.5 and pH 8.3 respectively). FAPGG hydrolysis was decreased by 82.5 % and 67.5 % by 5 mM EDTA and 5 mM DTE, respectively, and was totally inhibited by 50 nM of captopril or P-Glu-Trp-Pro-Arg-Pro-Glu-Ile-Pro-Pro and 500 nM of lisinopril. The optimum activity for FAPGG was at pH 6, chloride 50 mM and zinc 250 M. In the different conditions tested, bradykinin, angiotensin I (Ang-I), II (Ang-II) and LHRH were competitors for FAPGG. Bradykinin and Ang-I were the best competitors and these substrates were more effective at pH 6 and 300 mM chloride. The enzyme cleaved Ang-I in Ang-II and the optimal conditions were with 300 mM chloride and pH 7.5. The relationship between carboxypeptidase activity in seminal plasma and the prediction of fertility of young rams was also researched: the results shown a correlation between sperm concentration and gACE activity in semen but showed no significant correlation between this activity and the fertility of the animal. Finally, we tested the role of ACE in fertilization: no difference in in vitro fertilization rate was observed in the presence of 100 M captopril. These results suggest that this sperm enzyme could act either on the female genital tract to improve sperm transport or plays a role during epididymal sperm maturation. 1. Gatti JL et al. Biol Reprod 1999; 60:937.
KEY WORDS: angiotensin-I converting enzyme , epididymal maturation, fertility, sheep
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