Sialyl glycoprotein distribution on the plasma membrane of ejaculated ram spermatozoa

Localization of sialyl residues on unfixed ejaculated ram sperm membrane using the direct covalent probes of either ferritin hydrazide or latex hydrazide revealed a unique regional distribution on the plasmalemma covering the sperm head only. Three different labelling zones were identified based on the intensity and the nature of the sialyl glycoconjugates: a patchy-like zone which included the plasma membrane overlaying the post-nuclear cap and the convex side of the apical body of the acrosome; highly ordered heavily labelled zones including the plasmalemma adjacent to the concave apical body of the acrosome and to the posterior part of the equatorial acrosomal segment; a paucity-labelling zone which included the plasma membrane underlying the principal acrosomal region and the anterior part of the equatorial acrosomal segment. The possible physiological role of the highly ordered labelled zones is discussed.