Occurrence of -SH containing molecules on the goat sperm external surface that are essential for flagellar motility

p-Chloromercuriphenylsulphonic acid (PCMPS), a thiol reagent which is believed not to enter the cells, strongly inhibits motility of freshly extracted goat cauda-epididymal sperm preparations containing epididymal plasma (EP). The inhibitory action of PCMPS is not due to its interaction with the -SH groups of the surrounding EP-proteins. Washed cells when pretreated with low concentration of PCMPS (25 microM) for a short period (6 min) lost motility completely when assayed in presence of EP. PCMPS-mediated inhibition of motility cannot be reversed with the addition of large excess of various-SH compounds. The data suggest that PCMPS binds with high affinity to the specific -SH group(s) of sperm ecto-sulfhydryl molecules to cause their inactivation irreversibly by altering their conformation and thereby destroys sperm motility.