66 FERTILIZATION 



& Montella's claim (1947) that the acid formed in cytolysing sea- 

 urchin eggs is phosphoric acid, and the inhibitory action of phlor- 

 rhizin on this reaction (Rothschild, 1939), the acid which diffuses 

 out of these eggs at fertilization is not phosphoric acid. Perhaps 

 we should take account of the possibility that no organic acid 

 diffuses out of the egg at fertilization, but that some ion exchange 

 reaction, involving H3O+, occurs. According to Cleland (1950^, 

 p. 314), who did not observe any acid production when rock-oyster 

 eggs were fertilized, 'experiments on cytolytic acid production . . . 

 suggested beyond reasonable doubt that most of the acid produc- 

 tion was non-metabolic' The word non-metabolic means non- 

 glycolytic; an exchange reaction would presumably come into the 

 'non-metabolic' category. Alternatively, the reaction 



hexokinase 



ATP + glucose > ADP + glucose-6-phosphate + H+ 



at pH 7, is one suggestive example of a means of producing acid 

 in the form of hydrogen ions.* 



It is a remarkable and disappointing fact that acid production 

 at fertilization has not been observed, assuming that anyone ex- 

 cept Cleland has looked for it, in eggs other than those of the sea- 

 urchin. 



The cytochrome system. After measurements of O.^ uptake and 

 R.Q., the next step might well be to investigate the activity of the 

 cytochrome system in fertilized and unfertilized eggs, as cyto- 

 chrome oxidase is the terminal enzyme in aerobic catabolism. We 

 can be virtually certain that cytochrome will be present, because 

 it has been found in all aerobic organisms which have so far 

 been examined ; but confusion about the existence of cytochrome 

 in sea-urchin eggs and its role, if any, in fertilization, has 

 arisen for two reasons. First, because many workers have failed 

 to observe cytochrome spectroscopically in sea-urchin eggs; it 

 was not until these eggs were examined spectroscopically at the 

 temperature of liquid air (Rothschild, 1949a), a technique which 



* When considering increases in O2 uptake at fertilization and reactions 

 involving ATP, the student should note that it", at fertilization, ATP is broken 

 down with liberation of ADP, oxidations may be facilitated, as reactions of the 

 type 



AH2 + B — >A + BH, 



very often cannot take place, unless they occur in the following way 



AH2 + B + ADP + P — > A + BHa + ATP 



