Transfer of aminopeptidase activity from prostasomes to sperm

Prostasomes are membranous vesicles (150-200 nm diameter) present in human semen. They are secreted by the prostate and contain large amounts of cholesterol, sphingomyelin and Ca2+. In addition, some of their proteins are enzymes. Prostasomes enhance the motility of ejaculated spermatozoa and are involved in a number of additional biological functions. It has been demonstrated that lipid can be transferred from prostasomes to sperm by a fusion process occurring at slightly acidic pH. In this paper, we show that an aminopeptidase activity is transferred from prostasome to sperm. This may be of particular interest since it indicates the involvement of protein in the process of fusion and because sperm may acquire new membrane-bound proteins by this procedure.