GILBERT H. MUDGE 



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ing solution. No experiments were reported in wliich the mitochondria were 

 washed repeatedly. As indicated in table 2, the specific activity of mitochondria 

 washed only once is about twice as high as that of particulates washed three 

 times, but additional washings up to five times produce no further changes. 



Table i. Effect of external k concentration on rate of k exchange 



For details of experimental procedure see Stanbury and Mudge (17). Osmotic pressure of 

 medium kept constant by adjusting NaCl concentration. Incubation at 25° C for 20 minutes; 

 mitochondria 'harvested' by 3 washes in chilled 0.15 m/1. NaCl. Specific activity ratio calcu- 

 lated as specific activity of mitochondrial K divided by specific activity of K of entire sj'stem. 

 The potassium concentration of the mitochondria before incubation was 0.94 mEq/gm N. 



Table 2. Effect of extent of washing on mitochondrial electrolyte 



For details of experimental procedure see reference (17). Incubation under aerobic con- 

 ditions for 20 minutes; at 25°C for experiment i and i°C for experiment 2. After incubation 

 the contents of paired Warburg cups (each containing 3 ml of medium plus mitochondria) 

 were pooled and then washed with 50 ml chilled 0.15 m/1. NaCl for the number of times 

 indicated. The potassium concentration of the mitochondria before incubation was .86 

 mEq/gm N. 



The constant value for non-exchanged mitochondrial potassium suggests that 

 the additional washing procedures have removed residual incubation medium 

 from between the particles. Differences in techniques of centrifugation do not 

 permit any re-interpretation of the results of Bartley and Davies on the basis 

 of the results shown here. However, it is clear that the more vigorous washing 



