SPERM PLASMA-MEMBRANE REMODELING DURING SPERMIOGENETIC MATURATION IN MEN - RELATIONSHIP AMONG PLASMA-MEMBRANE BETA-1,4-GALACTOSYLTRANSFERASE, CYTOPLASMIC CREATINE-PHOSPHOKINASE, AND CREATINE-PHOSPHOKINASE ISOFORM RATIOS

Sperm creatine phosphokinase (CK) concentrations and the synthesis of the CK-M isoform reflect normal spermiogenesis and predict maturity an d fertilizing potential of ejaculated human spermatozoa. Immature sper matozoa, characterized by cytoplasmic retention and low CK-M to CK-B i soform ratios, are deficient in zona binding and fail to cause pregnan cies; Because these sperm lack zona-binding ability, we examined in th is study whether beta 1,4-galactosyltransferase (GalTase), a key eleme nt of sperm-zona interactions in mice, is diminished in immature human sperm. Unexpectedly, GalTase was overexpressed in immature sperm rela tive to mature sperm: the levels of cytoplasmic CK and plasma membrane GalTase were positively correlated (r = 0.78, p < 0.001, n = 88). Spe rm populations with various levels of cellular maturity, prepared by P ercoll gradients, had different CK and GalTase concentrations, but wit hin each subpopulation the relationship between CK and GalTase was mai ntained (p < 0.01-0.001). GalTase activities in intact and vortex-disr upted sperm fractions were similar, showing that GalTase is present on the surface membrane of human sperm - similar to the situation in all other species assayed. The changes previously reported by our laborat ory in zona-binding ability and lipid peroxidation rates (which occur simultaneously with cytoplasmic extrusion), decline in CK activity, an d increased expression of the CK-M isoform are suggestive of a remodel ing of the sperm surface concomitant with cytoplasmic maturation. The changes reported here in GalTase expression on the surface of maturing spermatozoa prove this hypothesis.