Effects of epididymal maturation, zinc (II) and copper (II) on the reactive sulfhydryl content of structural elements in rat spermatozoa

Abstract

The sulfhydryl content of rat spermatozoa at different stages of their maturation in the epididymis was determined by alkylation with 14C-iodoacetamide. Inhibition of this reaction by reagents having an affinity for thiols verified its specificity. The results support previous conclusions that epididymal maturation in eutherian mammals involves oxidation of -SH groups to -S-S- crosslinks in sperm heads and tails, imparting unusual stability to these structures. The heads and tails of immature rat spermatozoa displayed more than 20 and 5 times as many reactive -SH groups respectively as did those of mature spermatozoa. Fractionation of sonicated spermatozoa revealed that most of the reactive thiols are in the tails. Zn 2+, Cu 2+ and Cd 2+ inhibited the alkylation of -SH groups by iodoacetamide. Although the Zn 2+ inhibition could be reversed by EDTA, the effect of Cu 2+, believed to involve oxidation, was not reversible and could be largely prevented by a sufficient excess of Zn 2+. Thus, Zn 2+ may retard the oxidation of sperm -SH groups in vivo.