SOME PROPERTIES OF SPERM EXTRACTS AND THEIR RELATIONSHIP TO THE FERTILIZATION REACTION IN ARBACIA PUNCTULATA

Abstract

1. Sperm extracts of Arbacia, prepared by heating and filtering sperm suspensions in sea water, irreversibly agglutinate eggs of the same species. The reaction is characterized grossly by a dense coagulation of the ova and microscopically by the appearance of an "agglutination membrane" at the periphery of the egg jelly. Sperm extracts agglutinate both jelly and cortex of unfertilized, fertilized, living or dead ova. 2. The "egg-agglutinating substance" is fixed by the jelly and removed from solution. It is found only in extracts of sperm and cannot be extracted from any other cells or tissues of the sea-urchin, is not secreted by sperm into sea water, and is not present in extracts of old sperm. The egg-agglutinating substance is colorless, non-dialysable, colloidal, highly thermostable, disintegrates on standing, is preserved best at low temperatures, and does not give the usual protein tests. On extracting sperm with hot or cold alcohol-ether, the egg-agglutinating substance is found in the protein residue but not in the lipid extract. Mg and Ca ions are the only ions of sea water which are essential to the extraction of the egg-agglutinating substance, no specific anions taking part in the process. Sperm extracts made in distilled or tap water are inert. 3. Sperm extracts inactivate the sperm-agglutinating power of Arbacia fertilizin, the capacity for inactivation varying directly with the concentration of extract. The "fertilizin inactivator" has many properties in common with the egg-agglutinating substance. Loss of fertilizing power from aging sperm suspensions parallels the loss of the egg-agglutinating substance and fertilizin inactivator from extracts of these suspensions. 4. Sperm extracts block fertilization in Arbacia by a direct effect on each gamete: (a) Sperm suspensions in sperm extracts rapidly lose their fertilizing power as measured by their ability to fertilize fresh eggs in sea water. The extracts thus block fertilization by a direct action on the spermatozoön. (b) The fertilizability of jellyless eggs is greatly decreased after exposure to sperm extracts, which exert an inhibitory effect on the cortex. (5) Arbacia embryos are instantly paralysed and agglutinated by sperm extracts. Eggs which are fertilized in extracts cease developing before the motile blastula stage but this effect is partially removed by transferring the eggs to sea water. 6. All attempts to activate Arbacia eggs by immersion in sperm extracts have been unsuccessful. 7. It is suggested that the agglutination of eggs and the inactivation of fertilizin by sperm extracts represent two effects of a single active substance extracted from sperm. Theoretical and experimental evidence is presented that this substance probably plays a definite role in the fertilization reaction.