THE METABOLISM OF EGGS, II 73 



the presence of o-iM-NaF, which would make it most unUkely that 

 any glycolysis would have been observed. In any case, rather low 

 concentrations of iodoacetate were used and little time was allowed 

 for the development of the inhibition. The hexose monophosphate 

 shunt. Table 14A, will, of course, be just as sensitive to iodo- 

 acetate as the glycolytic pathway. If, on the other hand, the hexose 

 monophosphate shunt is not involved in the terminal part of the 

 glycolytic pathway, iodoacetate should not have any inhibitory 

 action, (c) The addition of hexose monophosphate caused a greater 

 stimulation of O2 uptake than hexose diphosphate. This observa- 

 tion also is the subject of dispute ; (d) significant amounts of the 

 phosphorylated intermediates of glycolysis, e.g. alkali-labile 

 phosphate (triose phosphate), could not be identified by Ba 

 fractionation of acid egg extracts; (e) triose phosphate dehydro- 

 genase was said to be absent by Jandorf & Krahl (1942). Table 

 12 shows that this is probably incorrect. 



To sum up, there are evidently two pathways by which carbo- 

 hydrate is broken down in the sea-urchin and oyster egg, the nor- 

 mal anaerobic and also an oxidative pathway ; except in the case of 

 Arbacia eggs, where the 'strength' of the latter mechanism appears 

 to be greater than that of glycolysis, at any rate in homogenates, we 

 do not know which mechanism predominates, though both prob- 

 ably function to a greater or lesser extent. 



Quite apart from being involved in the degradation of poly- 

 saccharides to provide phosphate bond energy, the hexose mono- 

 phosphate reaction may be concerned with entirely different 

 cellular activities. The reaction 



Nicotinamide riboside + phosphate ^ Nicotinamide + ribose-i -phosphate, 



discovered by Rowen & Romberg (195 1), suggests that the hexose 

 monophosphate reaction may be involved in nucleic acid meta- 

 bolism, on the synthetic and not the catabolic side. Some interest- 

 ing speculations about the role of this reaction in determination, 

 and, in particular, animalization, will be found in Hultin's review. 

 Studies on the Structural and Metabolic Background of Fertilization 

 and Development {ig ^2^). 



Transient changes in carbohydrate metabolism at fertilization. 

 ZieHnski (1939) and later Orstrom & Lindberg (1940) showed that 

 the 'glycogen' content of sea-urchin eggs decreases at fertilization ; 

 in terms of glucose, the breakdown is equivalent to 26 /x-moles/ioo 



