110 



Britton Chance 



dicoumarol or whether it can be observed with other un- 

 coupHng agents, we have made studies of the effect of DIB* : 

 Fig. 15A indicates the results of a series of experiments in 

 which the effect of DIB upon the steady state of cytochrome 

 b is compared with its effect upon respiration with glutamate 

 as substrate. The respiratory activity rises to a maximum at 

 4 fiM DIB, and to a half-maximal level at 2 \jm DIB. The 



Fig. 15 a. A comparison of the spectroscopic and 

 respiratory effects of DIB. Guinea-pig kidney 

 mitochondria, glutamate as substrate. (Experi- 

 ments carried out in collaboration with Dr. G. 

 Hollunger.) (Expt. no. 658a) 



change of steady state level of cytochrome h shows a signifi- 

 cantly different response: absorbancy increase reaches a 

 plateau only when inhibition is maximal. It is apparent that 

 two overlapping spectroscopic responses to DIB are involved. 

 One gives a spectroscopic change of magnitude similar to 

 that caused by ADP at concentrations of the uncoupling 

 agent which give maximal respiratory rate. The second is a 

 further increase in the oxidation of cytochrome h, which 

 continues until inhibition is complete. These two responses 



* Kindly donated by Dr. H. Lardy. 



