C. B. METZ 53 



centrifuging sperm (Southwick, 1939; see also Tyler, 1948a, for 

 further details). The active agent in these preparations is con- 

 sidered by most investigators to be antifertilizin, the sperm sur- 

 face receptor substance that combines with fertilizin at aggluti- 

 nation. According to the analysis of Tyler and of Runnstrom, 

 Tiselius, and Vasseur (see Tyler, 1948a, for review), the active 

 agent gives the usual protein tests, is relatively heat stable, 

 contains about 16% nitrogen, and can be prepared in electro- 

 phoretically homogeneous form. It is inactivated by proteolytic 

 enzymes. Ultracentrifugation, electrophoretic mobility, and iso- 

 electric precipitation studies indicate a molecule with an acid 

 isoelectric point and a molecular weight under 10,000. 



Unfortunately, this agent has been confused, as a result of ex- 

 periments of Hultin ( 1947b, 1949 ) , with the basic proteins ( pro- 

 tamines, histones) from sperm. Solutions of basic proteins are 

 readily prepared by acidifying a sperm suspension to pH 1 or 

 lower, separating the insoluble nucleic acid from the dissolved 

 basic protein by centrifugation and neutralizing the basic protein 

 containing supernate. Basic proteins characteristically combine 

 with a wide variety of substances and cells, precipitating the 

 former and agglutinating the latter. It is not suprising, therefore, 

 that sea urchin sperm basic protein agglutinates both the sperm 

 and the eggs of the homologous species (Metz, 1942b, 1949; 

 Hultin, 1947a ) as well as a variety of unrelated forms ( see Metz, 

 Foley, and Donovan, 1949, concerning specificity). Because of 

 the agglutinating action on sea urchin eggs and certain other 

 considerations, Hultin ( 1947b ) concluded that the egg agglu- 

 tinins prepared by freeze thawing, heating, or mild acid extrac- 

 tion of sperm are also basic protein, not the specific receptor 

 substance (antifertilizin) of the sperm surface. However, the 

 latter preparations agglutinate only eggs, whereas the basic 

 proteins agglutinate both sperm and eggs. Furthermore, the egg 

 agglutinating action of antifertilizin is destroyed by the basic 

 protein extraction procedure (pH 1 or lower), and mixture of 

 the two extracts results in mutual neutralization (Metz, 1949). 

 In view of these observations and the acid isoelectric point of 

 antifertilizin (Tyler, 1949; Runnstrom, Tiselius, and Vasseur, 



