104 Britton Chance 



of 1 [iM Og/sec. After the added ADP is expended, the 

 respiratory rate falls by a factor of about 25. Addition of 

 385 [JLM calcium accelerates the respiration to 1-7 [xm Og/sec. 

 It should be noted that calcium gives a higher rate than that 

 obtained with ADP alone. After approximately 20 seconds, 



GPL Mw plus glutamate in 

 isotonic salts (K"^ free) 

 l35pM 

 ADP 385ijM 





Ca++ 



Fig. 10. Comparison of the effects of ADP 

 and calcium upon respiratory rate in 

 guinea-pig liver mitochondrial suspensions 

 (GPL Mw). The vibrating platinum elec- 

 trode (see Fig. 1) is used to record the 

 respiratory rates as a function of time. 

 Starting at the left-hand edge of the 

 figure, decreasing oxygen concentrations 

 are recorded in response to oxygen utiliza- 

 tion caused by addition of ADP and cal- 

 cium (Expt. no. 466c) 



the respiration comes spontaneously to a halt, the control 

 ratio in this case being approximately 40. A further addition 

 of 400 [xM calcium causes an acceleration of respiratory rate to 

 1 • 5, but at the end of 20 seconds, instead of falling to zero, it 

 proceeds at • 8 for the remainder of the experiment ; respira- 

 tory control is never regained. 



The calcium concentration for maximal stimulation of 

 respiratory activity depends upon the magnesium concentra- 



