Binding of starfish and sea cucumber sperm attractants to whole sperm and sperm fragments

Abstract Binding of starfish and sea cucumber sperm attractants to whole, living spermatozoa and to separated, purified, sperm heads and tails was measured by assaying for loss of sperm attracting activity from solution. Starfish sperm attractant bound mainly to whole sperm or isolated sperm tails and much less, or not at all, to isolated sperm heads. Binding of starfish attractant to sea cucumber sperm or sperm fragments did not occur, nor did sea cucumber sperm attractant bind to starfish sperm or sperm fragments. However, sea cucumber attractant bound equivalently to separated sea cucumber sperm heads and tails. Starfish sperm attractant remained bound to whole sperm or isolated sperm tails if they were frozen‐thawed, but was released if the sperm or sperm fragments were heated. Starfish attractant did not bind to sperm that was previously killed by heat or freezing and thawing but did bind to formalin‐fixed, sea water‐washed sperm. Removal of the sperm membrane using Triton X‐100 eliminated the ability to bind sperm attractant. Although the ratio of the surface areas of tails to heads was approximately 1.5 to 1, up to 10 times more sperm attractant bound to starfish sperm tails than to heads. These results are similar to the binding pattern of the motility‐activating, egg jelly‐derived peptides speract (SAP‐I) and alloresact (SAP‐IIB) to sea urchin sperm heads and tails. They suggest that starfish and sea cucumber sperm attractants bind to sperm membranes in a manner similar to the sperm activating peptides of sea urchins. © 1994 Wiley‐Liss, Inc.