Ram spermatozoa freed from seminal plasma by a dextran ‘swim-up’
procedure were incubated with Tween 20 and fractionated into motile (PEG-rich)
and stationary (dextran-rich) fractions by centrifugal countercurrent
distribution (CCCD) in an aqueous dextran–Ficoll– polyethylene
glycol (PEG) two-phase system. Increasing concentrations of Tween 20 resulted
in greater amounts of extracted protein and lower cell viability. Addition of
bull seminal plasma increased the proportion of live cells, whereas ram
seminal plasma increased the proportion of stationary cells. Proteins isolated
from each type of seminal plasma restored the CCCD profile of treated
spermatozoa to the right, this effect being reduced when proteins were
thermally denatured. Bovine serum albumin induced a slight displacement to the
left. No restoration of profile was achieved when ram spermatozoa were exposed
to proteins from bull seminal plasma in the presence of protein-free ram
seminal plasma. Adsorption of seminal plasma proteins by spermatozoa
previously stripped of surface proteins by exposure to detergent reversed the
detergent effect on motility. The findings are consistent with the concept
that ram seminal plasma contains a factor that interferes with protein
adsorption on the cell surface and prevents the protective effect of seminal
plasma proteins on maintenance of cell viability