784 15. EFFECTS OF VARIOUS FACTORS ON INHIBITION 



in the inhibition over this ranj^e is about 7%. Unfortunately, the concen- 

 trations of cyanide used were strongly inhibitory — the average inhibition 

 for five species at 28. 5^ was 87% with 1 niM cyanide — so that changes 

 due to temperature variation would not be so marked as they might have 

 been if the inhibition had been around 50% or lower. In some species only 

 stimulation of the respiration by cyanide was observed and in these cases 

 a rise in temjjerature usually increased the stimulation significantly; for 

 example, in Trypcuiosoina equipenlum, 1 \\\M cyanide stimulated 5% at 

 28.50 and 52% at 37.5°. Whether this stimulation is the result of the me- 

 tabolism of cyanide is not known. 



It may be noted that a rise in the temperature slightly decreased the 

 cyanide inhibition of frog muscle and slightly increased the inhibition of 

 trypanosomes. The effects of the temperature will depend not only on the 

 temperature sensitivity of the respiratory inhibition, but also on the be- 

 havior of the cyanide-resistant fraction of the respiration. It is quite likely 

 that tlie ratio between the sensitive and resistant fractions of respiration 

 will change with temperature. The control respiration of the frog muscle 

 preparation rose from 49.1 at 20^ to 83.7 at 30° and then fell to 29.9 at 

 40°. It would be surprising if the character of the respiration did not 

 also change over this range. That is to say, the changes observed here 

 cannot be immediately attriljuted to the temperature dependence of the 

 inhil)ition of cytochrome oxidase by cyanide. 



{B) Respiratory stimulation by 'lA-dinitiophcnol. The respiratory stimu- 

 lation induced by 2,4-dinitroplienol (DNP) as a result of its uncoupling of 

 oxidative phosphorylation has been found to be related to the temperature. 

 Early work had shown that the calorigenic action of DNP in wliole animals 

 was decreased by exposure to cold (Giaja and Dimitrijevic, 1933; Tainter, 

 1934) but it was subsequently demonstrated that DNP depressed shivering 

 and other responses to cold exposure, and when this was corrected for, it 

 was found that the calorigenic action of DNP was increased during hypo- 

 tliermia (Hall et al., 1937). In the intact animal there are many factors that 

 may be involved, such as the release of epinephrine and the altered activ- 

 ities of the nervous system. Thus Fuhrman and Field (1942) investigated 

 the action of DNP on tlie respiration of tissue slices in order that these 

 other factors might be eliminated. The stimulation ratio for cerebral cor- 

 tex and kidney cortex is plotted in Fig. 15-8 as a function of the tempera- 

 ture, the DNP concentration being kept constant at 0.0335 mM. In both 

 tissues the stimulation is maximal at a certain temperature — 22° for 

 kidney and 32^ for brain — and disappears as the temperature rises above 

 40°. The fall with temperature increase might be readily interpreted as 

 resulting from the acceleration of the control respiration to the point where 

 it is not being limited by the phosphorylation reactions, but the decrease 

 at low temperatures is more difficult to understand. However, one cannot 



