50 EGG AND SPERM SUBSTANCES 



on Arhacia eggs. In sucrose solution, however, these and other 

 cross tests revealed no specificity (Hagstrom and Hagstrom, 

 1955). Egg antifertilizin specificity has not been tested in forms 

 other than echinoids. 



The agent is evidently a protein since it is insoluble in protein 

 precipitants and is inactivated by proteolytic enzymes (Tyler, 

 1940b, 1948a). According to Tyler (1948a) and Runnstrom, 

 Wicklund, and Low ( 1954 ) egg antifertilizin is quite heat 

 labile. The latter workers find that Arhacia lixula egg antiferti- 

 lizin is inactivated at 57° C in 45 mmutes (Hagstrom and Hag- 

 strom, 1955, report that the same antifertilizin is not inactive after 

 30 minutes at 100° C). 



The antifertilizin activity is associated with pigment containing 

 gi'anules (Monroy and Runnstrom, 1952; Wicklund, 1954a) of 

 the egg cytoplasm. These granules failed to sediment at 25,000g 

 in 45 minutes, but did form a precipitate in 45 minutes at 155,- 

 OOOg. Ultracentrifugal and electrophoretic analysis revealed two 

 components. In the ultracentrifuge only one of these was pig- 

 mented. The component with antifertilizin activity has not been 

 identified. Since treatment with ribonuclease appears to enhance 

 the antifertilizin activity of the granular fraction (Runnstrom, 

 Hagstrom, and Low, 1955), it is likely that the active agent is 

 bound to RNA granules. 



Egg antifertilizin may have a role in fertilization but as yet this 

 remains to be demonstrated. The agent can be extracted from 

 both fertilized and unfertilized eggs (Monroy and Runnstrom, 

 1952). It seems unlikely, then, that much, if any, of the antiferti- 

 lizin is bound during or participates in the activation changes of 

 the egg. 



Antifertilizin-treated eggs do not fertilize readily (Tyler, 1940b, 

 1948a), as might be expected, since the agent precipitates the 

 jelly of the egg in the form of a membrane. As Tyler ( 1940b ) has 

 shown, the membrane acts as a mechanical barrier to the sperm; 

 likewise fertilizability of jellyless eggs is inhibited. This effect 

 has been cited in the case of sperm antifertilizin in support of 

 an essential role of fertilizin in fertilization (Tyler and Metz, 

 1955). The argument applies equally well for egg antifertilizin. 



