Identification of a decapacitation factor in goat seminal plasma

Abstract

The seminal plasma is complex mixture of the secretions of the testis, epididymis and the accessory glands. The secretory proteins of the epididymal fluid as well as those of the accessory glands appear along with spermatozoa as semen at the time of ejaculation. Some of these proteins coat the sperm surface and prevent the premature activation of the spermatozoa in the female reproductive tract. The activation of spermatozoa, which requires the removal of sperm- coating proteins, is necessitated for the entry of the spermatozoa into the oocyte at the site of fertilization. The adsorption of radiolabelled seminal plasma proteins on the sperm surface showed an absence of high molecular weight proteins, thus suggesting the reorganization of the sperm surface proteins during the process of capacitation. The effect of lyophilized goat seminal plasma proteins revealed an inhibitory effect on the capacitation after an initial preincubation of 3.5 h. The absorption of radiolabelled seminal plasma proteins on the sperm surface showed an absence of high molecular weight proteins, thus suggesting the reorganization of the sperm surface proteins during the process of capacitation. The amount of protein for a 50% decrease in the acrosome reaction as compared to the control in a dose- dependent response, ID₅₀ is 2.45 mg. The factor is removed by the help of ultracentrifugation for 6 h and the pellet obtained showed an inhibitory effect at an initial preincubation of 3.5 h and the value of ID₅₀ determined is 1.25 mg. An apparent mechanism of capacitation involves the rearrangement of sperm surface proteins and removal of the factor by ultracentrifugation shows that it is a high molecular weight protein.