yS FERTILIZATION 



Bolognari (1952) on the glutathione content of sea-urchin eggs both 

 before and immediately after fertihzation. There are two morals to 

 be drawn from these new 'difficulties' in interpreting metabolic 

 changes at fertilization. First, the spectre of unreproducible or 

 contradictory results, which often haunts the biologist, may not 

 be so frightening as it sometimes seems ; secondly, in investigating 

 the various changes which occur at fertilization, we must not only 

 bear in mind species differences, but also the past history of the 

 material, for it is evident that the pre-fertilization history of eggs 

 influences metabolism during early development. 



Tricarboxylic acid cycle. The tricarboxylic acid cycle un- 

 doubtedly functions in sea-urchin, oyster (Cleland, 19506), and cer- 

 tain fish eggs. Oxaloacetate, succinate, a-ketoglutarate, glutamate 

 and citrate are rapidly oxidized (Crane & Keltch, 1949), while 

 Keltch et al. (1950) showed that a particulate cell-free system ob- 

 tained from unfertilized Arbacia eggs esterified orthophosphate 

 during the oxidation of Krebs cycle intermediates. These results 

 have been confirmed and extended by Yeas (1954), who also 

 demonstrated the inhibition of Oo uptake by malonate, and by 

 Cleland & Rothschild (19526), who showed that egg homogenates 

 oxidize pyruvate, the effect on O2 uptake being more pronounced 

 when the formation of pyruvate from endogenous substrate was 

 blocked by fluoride. The complete oxidation of pyruvate is cogent 

 evidence in favour of the tricarboxylic acid cycle, as the latter is 

 believed to be the only mechanism which will combust pyruvate 

 to CO2 and water in animal tissues. The oxidation of pyruvate 

 by sea-urchin eggs was also noted by Goldinger & Barron (1946) 

 and Krahl et al. (1942). 



Hishida & Nakano (1954) found that addition of the usual 

 Krebs cycle intermediates stimulated the Oo uptake of egg homo- 

 genates of Oryzias latipes; succinate had the greatest efi^ect, in- 

 creasing the endogenous Oo uptake by 500%. The Oo uptake of 

 these homogenates, with or without the addition of substrates, in- 

 creases twenty-four hours after fertilization. The authors interpret 

 this as showing that there is a synthesis of Krebs cycle enzymes at 

 this time, though they point out that this view conflicts with that 

 of Spiegclman & Steinbach (1945), who found that the O2 uptake 

 of frog's egg homogenates decreased as development went on. 

 The latter concluded that, at the beginning of development, the 

 respiratory enzymes in the egg were not saturated by their appro- 



