A. MONROY 173 



perimeiits with urea suggest that in these molecules H-bonds 

 may be more exposed after fertilization. The new configuration 

 appears to render them less susceptible to the attack of trypsin 

 and less easily denatured by heat. 



A question of considerable importance is whether as a part of 

 this process, end groups, viz., peptides or amino acids, are split 

 off. Some years ago Orstrom (1941) gave evidence of a slight but 

 statistically significant increase of the nonprotein N during the 

 first ten minutes following fertilization. A reinvestigation of this 

 problem is now in progress in om* laboratory. A positive answer 

 to it would make one consider the interesting analogy between 

 activation of the egg at the level of the protein molecules and the 

 activation of some enzymes (e.g., pepsin) in which it is known 

 that the transition from the pro- to the active enzyme is accom- 

 panied by the splitting off of a terminal peptide. One could then 

 speak of an activation of the egg proteins upon fertilization. It is 

 interesting to recall here that Hultin ( 1950 ) found a considerable 

 acceleration of the turnover of the egg proteins after fertilization. 



On the basis of some model experiments, a working hypothesis 

 has been presented concerning the nature of the cortical reaction 

 in the activation of the sea urchin egg (Maggio and Monroy, 

 1955; Monroy, 1956). It has been suggested that the key reac- 

 tion of the activation of the egg is the release, followed by the 

 inactivation, of a lysophosphatide-like substance in the cortex of 

 the egg as a result of the reaction with the fertilizing sperm or 

 of any activating treatment. It has also been shown (Tyler, Mon- 

 roy, Kao, and Grundfest, 1956) that coincident with fertilization 

 a change of the membrane potential of the egg occurs. However, 

 how this gioup of early phenomena can possibly be linked to the 

 changes in the proteins of the egg is at present obscure. 



REFERENCES 



Ceas, M. P., M. A. Impellizzeri, and A. Monroy. 1955. The action of 

 urea on some proteins of the unfertilized and fertilized sea urchin 

 egg. Exptl. Cell Research, 9, 366-69. 



Christensen, L. K. 1952. Denaturation and enzymatic hydrolysis of 



