THE METABOLISM OF EGGS, II 79 



priate substrates, although at a later stage in development they 

 were. This does not seem to be true in the case of the eggs of 

 Oryzias lattpes, in which the Japanese workers have found a pro- 

 nounced synthesis of cytochrome oxidase and phosphothiamine 

 during development. 



Fluoroacetate has only a small inhibiting effect, about 20% at 

 io~^M, on sea-urchin egg homogenates. As it is a powerful inhibitor 

 of acetate metabolism in some animal tissues, acetate metabolism 

 may only play a small part in the overall oxidative metabolism of 

 such systems ; but the student should remember that fluoro- 

 acetate inhibits the Krebs cycle at the citric acid stage, owing to 

 its conversion to fluorocitric acid. Fluoroacetate will, therefore, 

 inhibit any oxidation which is mediated through the Krebs cycle. 

 The acetate inhibition hypothesis is confirmed by Hultin's ex- 

 periments (19536) on the metabolic utilization of i-^^C-acetate in 

 sea-urchin embryos. Utilization is low in the early phases of 

 development, though the position is not the same later, when 

 visible diflFerentiation starts. This suggests that except perhaps 

 during the first few minutes after fertilization, fatty acid meta- 

 bolism may be of secondary importance in the early phases of 

 development. 



