ESTIMATION BY RADIATION INACTIVATION OF THE MINIMUM FUNCTIONAL SIZE OF ACROSOME-REACTION-INDUCING SUBSTANCE (ARIS) IN THE STARFISH, ASTERIAS-AMURENSIS

In the starfish Asterias amurensis, the jelly coat of the eggs contain s a glycoprotein essential for the induction of the acrosome reaction in homologous spermatozoa that is termed the acrosome-reaction-inducin g substance (ARTS). ARIS is a highly sulphated and fucose rich glycopr otein of extremely high molecular mass (> 10(4) kDa). ARTS was irradia ted with high-energy electrons in order to estimate the minimum size r equired for its biological activity. The minimum functional unit or ta rget size of ARTS was estimated to be c. 14 kDa by target size analysi s. ARIS was significantly disintegrated by the irradiation, yet the to tal sugar content was not apparently reduced. The binding of I-125-lab elled ARTS to spermatozoa competed with that of irradiated ARTS, altho ugh the affinity of ARIS was much reduced after irradiation.