THE METABOLISM OF EGGS, I 67 



Keilin & Hartree discovered in 1939 and which markedly inten- 

 sifies the various bands of cytochrome, that cytochrome was clearly 

 seen. The sea-urchin egg spectrum is atypical, as although band a 

 is present, the normal bands of b and c are replaced by one which 

 can be called b^. Yeas (1954) confirmed these observations. The 

 band of CO-cytochrome oxidase, or COa^, is too faint to be seen 

 with certainty, though cytochrome oxidase has been identified 

 by Krahl et al. (1941). The apparent absence of cytochrome 

 c — according to Borei (195 1), sea-urchin eggs must contain less 

 than 5 X io~* y/mg. dry matter — is surprising. But in view of 

 the reactions of fertilized and unfertilized eggs to inhibitors 

 of cytochrome oxidase and the increased O2 uptake observed in 

 the presence of dimethyl-^-phenylenediamine (Runnstrom, 1930), 

 we can be certain that cytochrome c, or a carrier which is function- 

 ally indistinguishable from it, is present in the sea-urchin egg. 

 Cytochrome c is present in the eggs of the rock-oyster (Cleland, 

 i%ob). According to Horowitz & Baumberger (1941), the eggs of 

 Urechis caupo do not contain cytochrome but an oxidizable and 

 reducible haem pigment, Urechrome, believed to act in a similar 

 way to cytochrome. In spite of this observation, a further examina- 

 tion of these eggs at the temperature of liquid air should be re- 

 warding. 



The second reason for the confusion about cytochrome in sea- 

 urchin eggs concerned the inability of early workers to recognise 

 that cyanide, which inhibits the reduction of ferri-«3, and CO, 

 which in the dark or green light inhibits the oxidation of ferro-%, 

 inhibit the respiration of unfertilized eggs. These early failures 

 were for the time being partly responsible for the seductive but 

 false idea that the cytochrome system does not function in the un- 

 fertilized egg but is 'thrown into circulation' following fertihzation 

 or parthenogenetic activation. It is now known, through the work 

 of Robbie (1946) and Rothschild (1949(2), that both cyanide and 

 CO reversibly inhibit the respiration of unfertilized sea-urchin 

 eggs. These observations prove that the cytochrome system is 

 present and functioning in these eggs. One of the difficulties en- 

 countered in the use of these inhibitors is that, at certain concen- 

 trations but not at others, both of them increase the Oo uptake of 

 unfertilized eggs, as Lindahl observed in 1940. The mechanism 

 of this eflPect is not clear in the case of cyanide. In the case of CO, 

 the eggs may oxidize CO as in heart muscle (Fenn & Cobb, 1932), 



