CLEAVAGE AND B L ASTU L ATI () N 



723 



peptide formation, described by Kavanau, is apparent I'rom tlie isolation of 

 Lactobocilhis casei growth factors, qualitatively different at different stages, by 

 Gustafson, Hjelte and Hasselberg (1952). 



Lundblad (1950) reported strong but ephemeral proteolysis at fertilization in 



1 2 4 6 8 10 12 14 15 16 17 18 19 



20 21 



Stage 



22 



Fig. 3. Average percentage changes of the insoluble and soluble (o. lA/ KCl-o.oi iM HAc) 

 protein-amino acids from their values in the unfertilized eggs of Paracentrotus lividus. Stages 

 are described in Fig. 2. The top curve indicates a total new protein synthesis of 63% of 

 that in the unfertilized egg. The next set of three curves indicates that 66% of the initial 

 store of insoluble proteins is utilized, suggesting that the remaining 34°o of insoluble 

 proteins are structural and other non-yolk protein ; during the same period, new insoluble 

 proteins reach 58.8% of the initial store. The lower set of curves indicate that 95.1% of the 

 initial soluble yolk protein is utilized, while new soluble protein increase amounts to 75.1% 

 of that originally present, indicating that almost all soluble proteins in the unfertilized egg 

 are yolk proteins, while those in the pluteus are new embryonic proteins. Depletion of 

 soluble proteins at stage 1 8 may be responsible for the drop in insoluble yolk protein between 

 stages 19 and 20. Note correlation of periods of protein synthesis with periods of yolk 

 protein decrease. (From Kavanau, 1954b.) 



Literature p. 744 



