Dialysis of diluted semen before cryopreservation is beneficial to sperm survival. This is due to removal of low molecular weight components from seminal plasma that are damaging to sperm. The apparent molecular weights (M(r)) of these components range between 1000 and 12,000 as estimated by gel permeation chromatography and electrophoresis. The detrimental effect on sperm motility is greatest with the components of M(r) between 5000 and 12,000 and with those of M(r) < 1500. Their effect on sperm motility was dependent on concentration. The small molecular weight components were derived from the high molecular weight components of seminal plasma through disaggregation under prescribed conditions.

Bovine seminal plasma proteins are in an aggregated form of high molecular weight in their native state. By immobilisation on a cation exchanger with exposure to disaggregating conditions (i.e., acetonitrile and low pH), the high-molecular-weight aggregates could be dissociated to slowly release the low-molecular-weight components. The anionic component released from the cation exchanger during disaggregation was collected by adsorption on a hydrophobic interaction column. The cationic component remaining on the cation exchanger was eluted with NaOH. Both components were found on gel permeation chromatography to be < 5 kDa. SDS-PAGE of the various fractions showed that components of low molecular weight were still in an aggregated form. These components resulting from the disaggregation process have detrimental effects on sperm motility and the effects were more substantial compared with that of whole seminal plasma. All the cationic components were significantly detrimental to sperm motility, especially the fractions of low molecular weight. The anionic fractions reduced sperm motility when in an aggregated state. The isolated anionic peptide was not detrimental in its free form. In all fractions the peptides tended to re-aggregate to a higher molecular weight under neutral conditions, however, the isolated anionic peptide (molecular weight < 1,500) failed to do so.