EXPERIMENTAL ANALYSIS 



literature in this field has been reviewed by Krahl^^s and CLOWES^^sa.) 

 These effects are fully reversible. Of these substances, 4, 6 dinitro- 

 orthocresol inhibits the Arbacia tgg in prophase or before (Scott^^'), 

 and those of Cumingia and Nereis at metaphase. In Asterias there is no 

 particular point of sensitivity, and after prophase the Arbacia ^gg may 

 be inhibited at any point. Dinitrophenol and halogenated phenols 

 inhibit cleavage in Arbacia, though there is no precise point at which 

 mitosis is specially sensitive to interruption (Clowes et alii^^^). 



The dual effect of these substances on respiration and cell division 

 are related. They occur at the same time when batches of eggs are 

 treated with increasing concentrations and are believed to be due to the 



2-0 



§^^ 



^h3 



1 2 3 1 2 3 1 2 3 



log (^ Molar concentration kIO ) 



Figure 69 Stimulation of oxygen consumption and block to cell division 

 of fertilized Arbacia eggs produced by various concentrations of substituted 

 phenols at 20° C (I). 2, 6-dinitro-4-chlorophenol. (II) 2, 6-dichloro- 

 4-nitrophenol. (Ill) 2, 6, dibromo-4-nitrophenol. Reagents were added 

 25 mins. after fertilization. Circles describe oxygen uptake, and dots repre- 

 sent cell division. From Krahl and Clowes^^^ {By courtesy, J. gen. Physiol.) . 



diversion of oxidative energy from phosphorylative synthesis to the 

 combustion of carbohydrate reserves. Thus Loomis and Lipmann^^* have 

 shown that dinitrophenol can uncouple phosphorylation and oxidation 

 in an isolated enzyme preparation,* and Villee et alii^^^ find that 

 dinitrophenol reduces the uptake of P^^ and its incorporation into 

 nucleic acids and phosphoproteins in the fertilized Arbacia egg. 



Comparable effects of dinitrophenols on other cells and tissues 

 are known in which functional activity depending on phosphate bond 



*Clowes^^^» has reported the preparation of cell-free oxidative and phosphorylating systems 

 from the eggs of Arbacia in which nitro- and halo-phenols stimulate respiration and inhibit 

 phosphorylation at the same concentrations as with normal fertilized eggs. 



