Decapacitation Factor

Decapacitation factor (DF) obtained from rabbit and bull seminal plasma has a molecular weight below 2000 and is estimated to be about 500 for the DF from the bull.27 df is said to be a naturally occurring antifertility substance since it does not possess toxicity for sperm but definitely prevents sperm from penetrating ova. 

The activity of several lytic enzymes, including sialidase, is necessary for fertilization. While sperm are in the seminal plasma, inhibitors of these enzymes are present in the decapacitation factor (DF). Sialidase was found to be a component of sperm acrosomes by Srivastava et aL (1970). They found sialidase activity and a sialidase-like factor which rendered bound sialic acid reactive in the thiobarbituric acid assay (Warren, 1959) but did not release it from the molecule and, upon purification, appeared to be converted to sialidase. An inhibitor of the sialidase-like factor was found in a partially purified DF preparation. The DF is lost during capacitation, which can be broadly defined to include the changes sperm undergo to enable them to penetrate the vitelline membrane of the egg. Gould et aL (1971) have proposed that the role of sialidase in fertilization is to alter the tertiary and quaternary structure of sialoglycoprotein present in the zona pellucida to cause the zona pellucida to be less penetrable by spermatozoa and serve to reduce or block polyspermy. 

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