A. MONROY 171 



respect to heat denaturation. To distinguish between denatured 

 and nondenatured proteins the sohibihty in an acid buffer of 

 high molarity was used. This buffer has been shown to induce 

 precipitation of denatured lactoglobuRn and serum albumin, 

 whereas when they are in the native condition these proteins stay 

 in solution ( Christensen, 1952 ) . In the case of the sea urchin egg 

 extracts, a large proportion of the extracted proteins is precipi- 

 tated by the buffer without any previous denaturing treatment, 

 and the amount of precipitate is greater in the case of the un- 

 fertilized eggs. Although this result does not allow one to draw 

 any conclusion as to the condition that makes such proteins sus- 

 ceptible to the salt buffer, it is nevertheless indicative of a differ- 



Fig. 1. Electrophoretic patterns after trypsin digestion of the fraction 

 precipitated at 50% saturation of ammonium sulfate from an extract of un- 

 fertilized (solid line) and fertilized (dotted line) eggs. (Redrawn from 

 an experiment of D'Amelio.) 



ence between the proteins of the unfertilized and of the newly 

 fertilized eggs. A difference between the two is also shown by 

 mere inspection of the precipitate which is flocculent and rapidly 

 settling in the former, whereas in the latter it is finely dispersed, 

 takes some time to appear, and settles only very slowly. The 

 total amount of precipitable proteins upon heating between 50° 

 and 60° C. followed by addition of the buffer is significantly 

 greater in the extracts of unfertilized than in those of fertilized 

 eggs. The same result has been obtained with the fraction pre- 

 cipitated by 50% saturation with ammonium sulfate (Giardina 

 and Monroy, 1955 ) . Two alternative explanations were presented 

 to account for these results, i.e., either a change occurred in the 

 molecular configuration of some proteins or a splitting of a large 

 complex present in the unfertilized egg took place. It was shown 



