116 



Britton Chance 



reduction of cytochrome b is indicated by the downward 

 sweep of the trace. Here, again, the platinum microelectrode 

 indicates the rapid initiation of respiration. 



Initiation of respiratory activity upon glucose addition is 

 also a rapid but somewhat more complicated reaction (Chance, 

 1954, 1955). An interesting result of the glucose experiments 

 is that pyridine nucleotide reduction at the level of glycer- 

 aldehyde-3-phosphate dehydrogenase can activate respiration. 

 The rapid reduction of mitochondrial cytochrome by cyto- 



IO;jM Og 



t 



34mM 

 Ethanol 



rodQ 

 428- 405 mp 



34m 

 Ethanol 



sec. 



sec. 



— r- 

 20 



Cytochrome b 



Pyridine nucleotides 



Fig. 18. A comparison of the kinetics of reduction of pyridine 

 nucleotide and cytochrome b of starved yeast cells caused by 

 the addition of ethanol. (Expt. no. 181) 



plasmic dehydrogenase may result from the permeability of 

 yeast mitochondria to reduced pyridine nucleotide formed in 

 the cytoplasm. On the other hand, there may be a much 

 closer organization of glycolytic and mitochondrial enzymes 

 within the cell than can be demonstrated in cell extracts. 



In flight muscle of the housefly, it is suggested that the 

 substrate level may control the respiratory activity (Chance 

 and Sacktor, 1958). 



Metabolic control through the phosphorylation system. The 

 more subtle aspects of metabolic regulations are not usually 

 revealed by the transition from the "starved" to the "fed" 

 state, but instead require the study of transition between 



