Phosphate Turnover and Pasteur Effect 257 



other. Without this cycle inorganic phosphate, adenosine 

 diphosphate (ADP) and ATP could not fulfil their important 

 catalytic functions in the cell. If, in the living cell, this equili- 

 brium were not maintained, all metabolism would cease within 

 a short time, due to lack of ATP if phosphorylation proceeded 

 too slowly as compared with dephosphorylation, or due to 

 lack of inorganic phosphate and ADP in the case of too rapid 

 phosphorylation. Thus dephosphorylation, which depends 

 directly on the energy requirement of the cell, may regulate 

 the catabolic processes and correlate them with the energy 



respiring cells fermenting cells 



(2(, - Dmitrophenol ) ^^^^^^^\ y^P^-'^^^^Nv 



Hrshc ^p With Glucose P p 



%^ 



respiratory chain 

 phosphorylation, 

 phosphorylation at sub- 

 strate level. 

 <v I dephosphorylation. 



Fig. 1. "Phosphate cycle" in living cells. 



requirement (cf. Lardy, 1955). The inhibition of fermentation 

 by oxygen would, therefore, depend on the following facts: 

 under aerobic conditions, respiration and fermentation must 

 share the dephosphorylation capacity which is completely 

 available for fermentation under anaerobic conditions. These 

 facts are represented schematically in Fig. 1, assuming 

 aerobic and anaerobic dephosphorylation to be equal. The 

 latter was confirmed by experiments with yeast cells (Lynen 

 and Koenigsberger, 1951). It seemed that the aerobic inhibi- 

 tion of fermentation was due to the decreased amount of 

 inorganic phosphate available for the triose phosphate de- 

 hydrogenation ; evidence in support of this was obtained by 

 phosphate analysis of respiring and fermenting yeast cells 



CELL METAB. — 9 



