88 



FERTILIZATION 



Lundblad has published an interesting series of papers showing 

 that proteolytic enzymes are activated transiently at fertilization (Fig. 

 15). Two of these enzymes, EI and EIII, can be activated in un- 

 fertilized egg homogenates by ribonuclease. Lundblad & Hultin 

 (1954) beHeve that EI and EIII are activated at fertilization by ribo- 

 nuclease, derived from the fertilizing spermatozoon or from the egg, 

 following the activation of egg ribonuclease by the fertilizing spermato- 

 zoon. EI and EIII are also activated by SH groups, which have an 

 inhibitory effect on EI I, as does heparin. These observations are not 



ER 



^ 



O 



FIG. 



15. — Activity of proteolytic enzymes in sea-urchin eggs. A, before fertiliza- 

 tion; B, at fertilization; C, at membrane elevation; D, immediately after 

 membrane elevation; E, ten minutes after membrane elevation. Three 

 enzymes, EI, EII and EIII, are involved in each period. After Lundblad 

 (1954^). 



incompatible with the ribonuclease hypothesis, as SH reagents 

 increase the activity of ribonuclease in liver (Roth, 1953), while 

 heparin inactivates sea-urchin egg ribonuclease (Lindvall & Carsjo, 

 1954). The most dominating feature of Lundblad's experiments is 

 the sharp activation of proteolytic enzymes during the elevation of the 

 fertilization membrane. It would, therefore, be of interest to investi- 

 gate the course of events in eggs treated with trypsin before fertiliza- 

 tion, so that membrane formation is suppressed. 



(16) Solubility of proteins in M-KCl decreases by 12%, 4-10 

 min. after f. A. piinctulata, S. purpiiratus (Mirsky, 1936). 



(16.1) New electrophoretic component appears in water ex- 

 tracts shortly after f. and disappears after 30 min. Ammonium 



