198 



Embryogenesis: Preparatory Phases 



way of carbohydrate breakdown in the sea 

 urchin egg, it has been suggested (Lindberg 

 and Ernster, '48) that this is through the 

 mechanism known as the hexose monophos- 

 phate shunt (Dickens, '38), but more re- 

 ent evidence (Yeas, '50; Cleland and Roths- 

 child, '52) shows the presence and opera- 

 tion of the conventional glycolytic mecha- 

 nisms. 



Sea urchin eggs are known to contain 

 diphosphopyridine nucleotide (Runnstrom, 

 '33; Jandorf and Krahl, '42) but no change 



is inhibited by cyanide. This might operate 

 by interference with the resynthesis of ATP. 

 While there is evidently no over-all change 

 in content of ATP (or other acid-soluble 

 phosphorus compounds) upon fertilization 

 in sea urchins (Runnstrom, '33; Orstrom and 

 Lindberg, '40; Lindberg, '43; Whiteley, '49), 

 this does not, of course exclude it as an im- 

 portant agent in the activation of the egg. 

 There is evidence (Harvey, '30; Runnstrom, 

 '30b; Barron, '32; Kitching and Moser, '40) 

 that sea urchin eggs can be fertilized or 



20 



180 



60 120 



MINUTES AFTER FERTILIZATION 



Fig. 65. Change in content of a glycogen-like polysaccharide (estimated as glucose) after fertilization in eggs 



of the sea urchin Paracentrotus lividus (from data of Orstrom and Lindberg, '40) . 



in the content of this coenzyme is found 

 upon fertilization. Sea urchin eggs also con- 

 tain an adenosinetriphosphatase (Runnstrom, 

 '33) and its activity has been found (Connors 

 and Scheer, '47) to be over twice as high in 

 homogenates prepared from fertilized eggs 

 as in those from unfertilized eggs. Since the 

 ATPase activity is increased by calcium this 

 difference might be correlated with the re- 

 lease of bound calcium (Heilbrunn, '43) 

 upon fertilization. The tracer experiments to 

 which reference was made above have also 

 shown that, as the labelled phosphate is 

 taken up by the fertilized egg, increasing 

 radioactivity is found in the adenosinetri- 

 phosphate (ATP) that is prepared from the 

 eggs. Studies of the distribution of the 

 labelled phosphate (Abelson, '48; Chambers 

 et al., '48; Whiteley, '49) have shown that 

 96 to 97 per cent is in the trichloroacetic acid- 

 soluble fraction (about a third of which is 

 probably ATP and ADP). It is of further 

 interest that the uptake of labelled phosphate 



artificially activated under anaerobic condi- 

 tions. It would be of interest to learn whether 

 or not ATP and other possible energy-yield- 

 ing agents decrease under such conditions. 



Fertilization in sea urchins also results in 

 the temporary (15 to 20 minutes) production 

 of an as yet unknown acid (Runnstrom, '30b, 

 '33; Orstrom, '35; Borei, '33; Laser and 

 Rothschild, '39) and in a temporary (10 

 minutes) increased production of ammonia 

 (Orstrom, '41). The exact significance of this 

 for fertilization is unknown. Orstrom has 

 also reported that fertilized eggs can produce 

 glutamine when ammonia and glumatic acid 

 are added, whereas unfertilized eggs lack 

 this ability. This is interpreted as reflecting 

 a general lack of synthetic ability on the 

 part of the unfertilized, in contrast to the 

 fertilized, egg. 



From the work of Orstrom and Lindberg 

 ('40) there appears to be a considerable 

 breakdown of a polysaccharide (that they 

 designate as, but which may not be, glyco- 



