76 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



activity can therefore be studied at constant calcium concentration with- 

 out fear that the pressure or temperature is changing the amount of 

 calcium-myosin complex through the calcium equilibrium. 



TEMPERATURE 



The hydrogen ion dependence of the pressure effect is strong evidence 

 for reversible denaturation. The temperature dependence of the ATP-ase 

 activity and of the pressure effect are consistent with reversible denatura- 



TEMPERATURE 

 38 30 20 10 



TEMPERATURE 



38 30 20 10 

 1 







3.2 M ATP 

 1.47 mM Ca 

 pH 8.4 



Fig. 3. Dependence of myosin ATP-ase activity on temperature (4). Left: activities 

 at atmospheric pressure. Heats calculated for successive straight-line portions of the 

 curve decrease with increasing temperature. Right: activities at atmospheric pres- 

 sure and at 9,000 pounds per square inch. 



tion, and reasonable heats can be calculated on this basis. They do not 

 by themselves establish that denaturation occurs. 



The activity depends on temperature as shown on the left of figure 3. 

 At first sight, the points fall on a reasonable straight line, as if tempera- 

 ture affects a simple rate process, according to the Arrhenius relation.^ 

 Closer examination, however, shows that the points depart systematically 

 from a: straight line, and the apparent heat of activation decreases as the 

 temperature increases. In bioluminescence and certain other processes (5, 

 7, 11) a similar but more pronounced departure is caused by reversible 

 denaturation. For myosin ATP-ase, the departure from linearity is small, 



^They were so reported in a preliminary note(lO). The best line corresponds to a 

 heat of activation of 12,400 cal/mole. 



