Control of Oxygen Utilization 119 



attached to glucose. Thus, it is apparent that 

 sufficient phosphate was available inside the cell to permit the 

 rapid restarting of respiration solely in response to an increase 

 of intracellular ADP concentration. The spectroscopic and 

 respiratory changes could not be attributed to the transport 

 of magnesium or calcium into the cell at the moment glucose 

 was added because the yeast was suspended in a calcium-free 

 buffer solution. 



Similar experiments show respiratory control to be a factor 



430-440m;j 



^Ioglo/I = 0.0005 



stim. \ - y 



1/15 seC: 



Fig. 20. Response of cytochrome b 

 component of frog's sartorious 

 muscle to a series of twitches. Each 

 twitch is indicated by the inter- 

 ruptions of the trace. Oxidation of 

 cytochrome b is indicated by an 

 upward deflexion. (Expt. no. 



W-15) (By courtesy of Dr. A. 

 Weber.) 



in the steady state metabolism in other tissues (ascites 

 tumour cells) (Chance and Hess, 1956). The glucose experi- 

 ment is perhaps the most useful test for ADP-limited control. 

 In muscular contraction, control due to ADP or phosphate 

 can be demonstrated by the spectroscopic response of the 

 cytochromes. An example of this is afforded by the oxidation 

 of cytochrome b of excised frog sartorius muscle caused by a 

 series of single contractions (Weber, 1957), which gives a 

 maximal steady state response (Fig. 20). At the same time, 

 utilization of the accumulated ADP or phosphate occurs and 



