INTERACTIONS BETWEEN ARBACIA SPERM AND S35—LABELLED FERTILIZIN

1. Reactions between Arbacia fertilizin and sperm were studied with preparations of S35-labelled fertilizin. Experiments consisted of mixing fertilizin and sperm, centrifuging the sperm from the suspension, and assaying the supernatant for radioactivity. In this way the absorption of fertilizin to sperm could be measured as a loss of radioactivity from the supernatant.2. Results of 10 experiments show that there was an initial absorption by sperm of all but 28% of the fertilizin. This was rapidly followed by a release of more than one-half the absorbed material.3. Sperm which have reacted with fertilizin do not absorb additional fertilizin upon further treatment with this substance.4. Fertilizin solutions which have reacted with sperm are not appreciably absorbed by fresh sperm.5. Dialysis shows that the S35-labelled material absorbed to and released from sperm is non-diffusible.6. Heterologous sperm from three species absorb Arbacia fertilizin but do not release it.7. The parallel between absorption and ...