GII.BKRT H. MUDGE 



119 



that well-washed susi)ensions normally contain significant amounts of nu- 

 cleotides (i, 11). 



It is of interest that other deleterious effects of orthophosphate on mito- 

 chondrial metabolism have been described within recent years. Pre-incubation 

 of suspensions in solutions containing phosphate disrupts the reactions of aerobic 

 phosphorylation (5). The well-known effect of orthophosphate in stimulating 

 respiration has been found to be rather transient and is followed after pro- 

 longed incubation by respiratory inhibition (16). It is of interest that depres- 

 sion of the mitochondrial level of potassium is the most sensitive of these phe- 

 nomena since it occurs while respiration is stimulated and while aerobic phos- 

 phorylation reactions are normal. 



The compound 2 ,4-dinitrophenol (DNP) is representative of a group of sub- 

 stituted phenols which uncouple aerobic phosphorylation; this action has been 

 extensively studied in mitochondrial preparations. Because DNP markedly in- 



Table 4. Effect of adenylic acid 



Separate experiments denoted by A and B. Aerobic incubation at 25° C as described (17). 

 Orthophosphate (60 ^im) and adenosine monophosphate (3 /jM) added as indicated; final 

 volume 3 ml. Osmotic pressure adjusted to constant value by change in NaCl. No consistent 

 effect on potassium exchange was noted in cups with AMP. For discussion see text. 



hibits potassium accumulation by slices of intact cells, it was anticipated that 

 a similar action would be demonstrable in the mitochondria. However, a more 

 complex effect was observed. The depression of potassium e.xchange at inter- 

 mediate concentrations of DNP was reversed when higher concentrations were 

 employed. This is associated with a comparable polyphasic action on phospho- 

 rylation. Intermediate concentrations of DNP inhibit both potassium e.xchange 

 and phosphorylation, while high concentrations increase potassium exchange 

 and also stimulate the formation of phospho-enol-pyruvate (16). Whether there 

 is any specific relationship between this phosphate ester and the transport of 

 potassium has not been established. Analyses of washed mitochondria reveal 

 a limited correlation between the levels of potassium and of this phosphate 

 ester (11). However, by the use of perm-selective membranes, Neuberg and 

 Tosteson (12) were unable to demonstrate selective binding of potassium by 

 phospho-enol-pyruvate. 



The general relationships which have been demonstrated between metabolic 



