Energy Exchange and Enzyme Development During Embryogenesis 529 



out, be completely unwarranted. Indeed, 

 Andresen, Holter, and Zeuthen ('44) have 

 shown that respiration in the absence of 

 cleavage in the egg of the ascidian Ciona 

 intestinalis is probably not significantly less 

 than in eggs in which cleavage is occurring. 

 These workers believe that the difference 

 in respiration is altogether due to difference 

 in developmental rate. 



A systematic study of the relation be- 

 tween oxidative metabolism and cell di- 

 vision, as revealed by the use of inhibitory 



confirmed this observation, but the period 

 of enhanced carbon dioxide output during the 

 mitotic cycle did not agree with that reported 

 by Lyon. It should be noted that the carbon 

 dioxide measured in these experiments may 

 not have had a respiratory origin at all; 

 it may have represented nothing more than 

 carbon dioxide released from sea water by 

 acids liberated from the egg (see p. 534). 

 In contrast with the findings of Lyon and 

 Vies, Meyerhof ('11) reported that calori- 

 metric determinations of energy exchange 



Table 16. The Effect of Various Chemical Agents on Cell Division and Res- 

 piration in the Sea Urchin Egg (Arbacia punctulata)* 



EFFECT ON CLEAVAGE 



RESIDUAL RESPIRATION AS 

 PERCENTAGE OF NORMAL 



Oxygen lack 

 KCN 



Carbon monoxide 

 Sodium azide 

 Sodium sulfide 

 Sodium sulfide 

 Diethyldithiocarbamate 

 Substituted phenols 

 Phenyl urethane 

 lodoacetate 

 Barbiturates 



Complete block 

 Complete block 

 Complete block 

 Complete block 



50% block 

 Complete block f 

 Complete block f 

 Complete block 

 Complete block 



90% block 

 Complete block 



20-30 



20-35 



30 



50 



90 



50 



100 



>100t 



70 



54 



20 



* Data for this table abstracted from Ki-ahl ('50). 

 t Cleavage block irreversible. 



J At a concentration slightly less than that required to produce complete reversible block to cell division, 

 various substituted phenols increase respiration from 20 to 260% above normal. 



and stimulatory substances, has been con- 

 ducted during the past two decades by 

 Clowes and Krahl and their collaborators. 

 Table 16 summarizes results for the sea 

 urchin egg abstracted from the compre- 

 hensive review of Krahl ('50). From the 

 data summarized in the table, and from 

 what is known about the specific action 

 of a number of the agents listed, it is possi- 

 ble to conclude that energy release during 

 cleavage involves the participation of the 

 cytochrome oxidase system and a system of 

 enzymes concerned with oxidative phos- 

 phorylation (see p. 540). It is clearly impos- 

 sible to state what the relative amount of 

 respiration necessary to svipport cell division 

 might be. 



A number of direct observations of res- 

 piratory changes during mitosis have been 

 made. As early as the turn of the century, 

 interest was focused on this problem through 

 the pioneer work of Lyon ('04) when he 

 found that carbon dioxide production after 

 cleavage of the sea urchin egg was con- 

 siderably greater than before. Vies ('22) 



during development of Strongylocentrotus 

 lividus eggs failed to reveal any evidence of 

 rhythmic variations that could be correlated 

 with cell division. Gray ('25) then investi- 

 gated the problem by making respiratory 

 measurements during cleavage in the eggs 

 of Echinus miliaris, but he concluded that 

 rhythmic changes specifically associated with 

 cell division were not superimposed on the 

 over-all course of oxygen consumption. Runn- 

 strom ('34) pointed out, however, that lack 

 of synchrony in cleavage in the large num- 

 bers of eggs itsed by Gray may have 

 obscured an intrinsic respiratory rhythm. 

 In a repetition of Gray's experiments Runn- 

 strom found that oxygen consumption was 

 higher during the early phases of the mi- 

 totic cycle than later in the process. 



The above observations were all made on 

 the eggs of sea urchins, but similar experi- 

 ments have been performed on amphibian 

 eggs. Trurnit (cited by Brachet, '50) meas- 

 ured heat production of Triton eggs by 

 actually inserting one of a delicate pair of 

 thermocouples into the egg, and he observed 



