LETHAL EFFECTS OF LYSENIN, A NOVEL PROTEIN ISOLATED FROM THE CELOMIC FLUID OF THE EARTHWORM EISENIA-FOETIDA, ON THE SPERMATOZOA OF THE AFRICAN CLAWED FROG AND THE MOUSE

Lysenin is a novel protein that has been isolated from the coelomic fl uid of the earthworm Eisenia foetida. It binds sphingomyelin (SM) spec ifically among various phospholipids. SM is known to be present on the plasma membranes of mammalian spermatozoa. To explore the function of SM on the plasma membranes, we examined the effects of lysenin on the spermatozoa of the frog (Xenopus laevis) and the mouse (Mus musculus) . Lysenin inhibited the motility of both frog and mouse spermatozoa an d killed them within a few minutes. Lysenin that had been incubated wi th SM-liposomes had slight or no lethal effects on frog and mouse sper matozoa. After mouse spermatozoa had been treated with lysenin, they i mmunoreacted with fluorescently labeled-lysenin-specific antibody alon g their entire length. The strongest immunofluorescence was observed i n the head region. These findings suggest that the lethal effects of l ysenin on spermatozoa are due to disturbance of the functions of the p lasma membrane that occurs upon binding of lysenin with SM on the memb rane. Lysenin should be a useful tool for analysis of the functions of SM not only in sperm physiology but also in cell membrane physiology in general.